+ png_fixed_point red_inverse, green_inverse, blue_scale;
+ png_fixed_point left, right, denominator;
+
+ /* Check xy and, implicitly, z. Note that wide gamut color spaces typically
+ * have end points with 0 tristimulus values (these are impossible end
+ * points, but they are used to cover the possible colors.)
+ */
+ if (xy.redx < 0 || xy.redx > PNG_FP_1) return 1;
+ if (xy.redy < 0 || xy.redy > PNG_FP_1-xy.redx) return 1;
+ if (xy.greenx < 0 || xy.greenx > PNG_FP_1) return 1;
+ if (xy.greeny < 0 || xy.greeny > PNG_FP_1-xy.greenx) return 1;
+ if (xy.bluex < 0 || xy.bluex > PNG_FP_1) return 1;
+ if (xy.bluey < 0 || xy.bluey > PNG_FP_1-xy.bluex) return 1;
+ if (xy.whitex < 0 || xy.whitex > PNG_FP_1) return 1;
+ if (xy.whitey < 0 || xy.whitey > PNG_FP_1-xy.whitex) return 1;
+
+ /* The reverse calculation is more difficult because the original tristimulus
+ * value had 9 independent values (red,green,blue)x(X,Y,Z) however only 8
+ * derived values were recorded in the cHRM chunk;
+ * (red,green,blue,white)x(x,y). This loses one degree of freedom and
+ * therefore an arbitrary ninth value has to be introduced to undo the
+ * original transformations.
+ *
+ * Think of the original end-points as points in (X,Y,Z) space. The
+ * chromaticity values (c) have the property:
+ *
+ * C
+ * c = ---------
+ * X + Y + Z
+ *
+ * For each c (x,y,z) from the corresponding original C (X,Y,Z). Thus the
+ * three chromaticity values (x,y,z) for each end-point obey the
+ * relationship:
+ *
+ * x + y + z = 1
+ *
+ * This describes the plane in (X,Y,Z) space that intersects each axis at the
+ * value 1.0; call this the chromaticity plane. Thus the chromaticity
+ * calculation has scaled each end-point so that it is on the x+y+z=1 plane
+ * and chromaticity is the intersection of the vector from the origin to the
+ * (X,Y,Z) value with the chromaticity plane.
+ *
+ * To fully invert the chromaticity calculation we would need the three
+ * end-point scale factors, (red-scale, green-scale, blue-scale), but these
+ * were not recorded. Instead we calculated the reference white (X,Y,Z) and
+ * recorded the chromaticity of this. The reference white (X,Y,Z) would have
+ * given all three of the scale factors since:
+ *
+ * color-C = color-c * color-scale
+ * white-C = red-C + green-C + blue-C
+ * = red-c*red-scale + green-c*green-scale + blue-c*blue-scale
+ *
+ * But cHRM records only white-x and white-y, so we have lost the white scale
+ * factor:
+ *
+ * white-C = white-c*white-scale
+ *
+ * To handle this the inverse transformation makes an arbitrary assumption
+ * about white-scale:
+ *
+ * Assume: white-Y = 1.0
+ * Hence: white-scale = 1/white-y
+ * Or: red-Y + green-Y + blue-Y = 1.0
+ *
+ * Notice the last statement of the assumption gives an equation in three of
+ * the nine values we want to calculate. 8 more equations come from the
+ * above routine as summarised at the top above (the chromaticity
+ * calculation):
+ *
+ * Given: color-x = color-X / (color-X + color-Y + color-Z)
+ * Hence: (color-x - 1)*color-X + color.x*color-Y + color.x*color-Z = 0
+ *
+ * This is 9 simultaneous equations in the 9 variables "color-C" and can be
+ * solved by Cramer's rule. Cramer's rule requires calculating 10 9x9 matrix
+ * determinants, however this is not as bad as it seems because only 28 of
+ * the total of 90 terms in the various matrices are non-zero. Nevertheless
+ * Cramer's rule is notoriously numerically unstable because the determinant
+ * calculation involves the difference of large, but similar, numbers. It is
+ * difficult to be sure that the calculation is stable for real world values
+ * and it is certain that it becomes unstable where the end points are close
+ * together.
+ *
+ * So this code uses the perhaps slighly less optimal but more understandable
+ * and totally obvious approach of calculating color-scale.
+ *
+ * This algorithm depends on the precision in white-scale and that is
+ * (1/white-y), so we can immediately see that as white-y approaches 0 the
+ * accuracy inherent in the cHRM chunk drops off substantially.
+ *
+ * libpng arithmetic: a simple invertion of the above equations
+ * ------------------------------------------------------------
+ *
+ * white_scale = 1/white-y
+ * white-X = white-x * white-scale
+ * white-Y = 1.0
+ * white-Z = (1 - white-x - white-y) * white_scale
+ *
+ * white-C = red-C + green-C + blue-C
+ * = red-c*red-scale + green-c*green-scale + blue-c*blue-scale
+ *
+ * This gives us three equations in (red-scale,green-scale,blue-scale) where
+ * all the coefficients are now known:
+ *
+ * red-x*red-scale + green-x*green-scale + blue-x*blue-scale
+ * = white-x/white-y
+ * red-y*red-scale + green-y*green-scale + blue-y*blue-scale = 1
+ * red-z*red-scale + green-z*green-scale + blue-z*blue-scale
+ * = (1 - white-x - white-y)/white-y
+ *
+ * In the last equation color-z is (1 - color-x - color-y) so we can add all
+ * three equations together to get an alternative third:
+ *
+ * red-scale + green-scale + blue-scale = 1/white-y = white-scale
+ *
+ * So now we have a Cramer's rule solution where the determinants are just
+ * 3x3 - far more tractible. Unfortunately 3x3 determinants still involve
+ * multiplication of three coefficients so we can't guarantee to avoid
+ * overflow in the libpng fixed point representation. Using Cramer's rule in
+ * floating point is probably a good choice here, but it's not an option for
+ * fixed point. Instead proceed to simplify the first two equations by
+ * eliminating what is likely to be the largest value, blue-scale:
+ *
+ * blue-scale = white-scale - red-scale - green-scale
+ *
+ * Hence:
+ *
+ * (red-x - blue-x)*red-scale + (green-x - blue-x)*green-scale =
+ * (white-x - blue-x)*white-scale
+ *
+ * (red-y - blue-y)*red-scale + (green-y - blue-y)*green-scale =
+ * 1 - blue-y*white-scale
+ *
+ * And now we can trivially solve for (red-scale,green-scale):
+ *
+ * green-scale =
+ * (white-x - blue-x)*white-scale - (red-x - blue-x)*red-scale
+ * -----------------------------------------------------------
+ * green-x - blue-x
+ *
+ * red-scale =
+ * 1 - blue-y*white-scale - (green-y - blue-y) * green-scale
+ * ---------------------------------------------------------
+ * red-y - blue-y
+ *
+ * Hence:
+ *
+ * red-scale =
+ * ( (green-x - blue-x) * (white-y - blue-y) -
+ * (green-y - blue-y) * (white-x - blue-x) ) / white-y
+ * -------------------------------------------------------------------------
+ * (green-x - blue-x)*(red-y - blue-y)-(green-y - blue-y)*(red-x - blue-x)
+ *
+ * green-scale =
+ * ( (red-y - blue-y) * (white-x - blue-x) -
+ * (red-x - blue-x) * (white-y - blue-y) ) / white-y
+ * -------------------------------------------------------------------------
+ * (green-x - blue-x)*(red-y - blue-y)-(green-y - blue-y)*(red-x - blue-x)
+ *
+ * Accuracy:
+ * The input values have 5 decimal digits of accuracy. The values are all in
+ * the range 0 < value < 1, so simple products are in the same range but may
+ * need up to 10 decimal digits to preserve the original precision and avoid
+ * underflow. Because we are using a 32-bit signed representation we cannot
+ * match this; the best is a little over 9 decimal digits, less than 10.
+ *
+ * The approach used here is to preserve the maximum precision within the
+ * signed representation. Because the red-scale calculation above uses the
+ * difference between two products of values that must be in the range -1..+1
+ * it is sufficient to divide the product by 7; ceil(100,000/32767*2). The
+ * factor is irrelevant in the calculation because it is applied to both
+ * numerator and denominator.
+ *
+ * Note that the values of the differences of the products of the
+ * chromaticities in the above equations tend to be small, for example for
+ * the sRGB chromaticities they are:
+ *
+ * red numerator: -0.04751
+ * green numerator: -0.08788
+ * denominator: -0.2241 (without white-y multiplication)
+ *
+ * The resultant Y coefficients from the chromaticities of some widely used
+ * color space definitions are (to 15 decimal places):
+ *
+ * sRGB
+ * 0.212639005871510 0.715168678767756 0.072192315360734
+ * Kodak ProPhoto
+ * 0.288071128229293 0.711843217810102 0.000085653960605
+ * Adobe RGB
+ * 0.297344975250536 0.627363566255466 0.075291458493998
+ * Adobe Wide Gamut RGB
+ * 0.258728243040113 0.724682314948566 0.016589442011321
+ */
+ /* By the argument, above overflow should be impossible here. The return
+ * value of 2 indicates an internal error to the caller.
+ */
+ if (!png_muldiv(&left, xy.greenx-xy.bluex, xy.redy - xy.bluey, 7)) return 2;
+ if (!png_muldiv(&right, xy.greeny-xy.bluey, xy.redx - xy.bluex, 7)) return 2;
+ denominator = left - right;
+
+ /* Now find the red numerator. */
+ if (!png_muldiv(&left, xy.greenx-xy.bluex, xy.whitey-xy.bluey, 7)) return 2;
+ if (!png_muldiv(&right, xy.greeny-xy.bluey, xy.whitex-xy.bluex, 7)) return 2;
+
+ /* Overflow is possible here and it indicates an extreme set of PNG cHRM
+ * chunk values. This calculation actually returns the reciprocal of the
+ * scale value because this allows us to delay the multiplication of white-y
+ * into the denominator, which tends to produce a small number.
+ */
+ if (!png_muldiv(&red_inverse, xy.whitey, denominator, left-right) ||
+ red_inverse <= xy.whitey /* r+g+b scales = white scale */)
+ return 1;
+
+ /* Similarly for green_inverse: */
+ if (!png_muldiv(&left, xy.redy-xy.bluey, xy.whitex-xy.bluex, 7)) return 2;
+ if (!png_muldiv(&right, xy.redx-xy.bluex, xy.whitey-xy.bluey, 7)) return 2;
+ if (!png_muldiv(&green_inverse, xy.whitey, denominator, left-right) ||
+ green_inverse <= xy.whitey)
+ return 1;
+
+ /* And the blue scale, the checks above guarantee this can't overflow but it
+ * can still produce 0 for extreme cHRM values.
+ */
+ blue_scale = png_reciprocal(xy.whitey) - png_reciprocal(red_inverse) -
+ png_reciprocal(green_inverse);
+ if (blue_scale <= 0) return 1;
+
+
+ /* And fill in the png_XYZ: */
+ if (!png_muldiv(&XYZ->redX, xy.redx, PNG_FP_1, red_inverse)) return 1;
+ if (!png_muldiv(&XYZ->redY, xy.redy, PNG_FP_1, red_inverse)) return 1;
+ if (!png_muldiv(&XYZ->redZ, PNG_FP_1 - xy.redx - xy.redy, PNG_FP_1,
+ red_inverse))
+ return 1;
+
+ if (!png_muldiv(&XYZ->greenX, xy.greenx, PNG_FP_1, green_inverse)) return 1;
+ if (!png_muldiv(&XYZ->greenY, xy.greeny, PNG_FP_1, green_inverse)) return 1;
+ if (!png_muldiv(&XYZ->greenZ, PNG_FP_1 - xy.greenx - xy.greeny, PNG_FP_1,
+ green_inverse))
+ return 1;
+
+ if (!png_muldiv(&XYZ->blueX, xy.bluex, blue_scale, PNG_FP_1)) return 1;
+ if (!png_muldiv(&XYZ->blueY, xy.bluey, blue_scale, PNG_FP_1)) return 1;
+ if (!png_muldiv(&XYZ->blueZ, PNG_FP_1 - xy.bluex - xy.bluey, blue_scale,
+ PNG_FP_1))
+ return 1;
+
+ return 0; /*success*/
+}
+
+int png_XYZ_from_xy_checked(png_structp png_ptr, png_XYZ *XYZ, png_xy xy)
+{
+ switch (png_XYZ_from_xy(XYZ, xy))
+ {
+ case 0: /* success */
+ return 1;
+
+ case 1:
+ /* The chunk may be technically valid, but we got png_fixed_point
+ * overflow while trying to get XYZ values out of it. This is
+ * entirely benign - the cHRM chunk is pretty extreme.
+ */
+ png_warning(png_ptr,
+ "extreme cHRM chunk cannot be converted to tristimulus values");
+ break;
+
+ default:
+ /* libpng is broken; this should be a warning but if it happens we
+ * want error reports so for the moment it is an error.
+ */
+ png_error(png_ptr, "internal error in png_XYZ_from_xy");
+ break;
+ }
+
+ /* ERROR RETURN */
+ return 0;
+}
+#endif
+
+void /* PRIVATE */
+png_check_IHDR(png_structp png_ptr,
+ png_uint_32 width, png_uint_32 height, int bit_depth,
+ int color_type, int interlace_type, int compression_type,
+ int filter_type)
+{
+ int error = 0;
+
+ /* Check for width and height valid values */
+ if (width == 0)
+ {
+ png_warning(png_ptr, "Image width is zero in IHDR");
+ error = 1;
+ }
+
+ if (height == 0)
+ {
+ png_warning(png_ptr, "Image height is zero in IHDR");
+ error = 1;
+ }
+
+# ifdef PNG_SET_USER_LIMITS_SUPPORTED
+ if (width > png_ptr->user_width_max)
+
+# else
+ if (width > PNG_USER_WIDTH_MAX)
+# endif
+ {
+ png_warning(png_ptr, "Image width exceeds user limit in IHDR");
+ error = 1;
+ }
+
+# ifdef PNG_SET_USER_LIMITS_SUPPORTED
+ if (height > png_ptr->user_height_max)
+# else
+ if (height > PNG_USER_HEIGHT_MAX)
+# endif
+ {
+ png_warning(png_ptr, "Image height exceeds user limit in IHDR");
+ error = 1;
+ }
+
+ if (width > PNG_UINT_31_MAX)
+ {
+ png_warning(png_ptr, "Invalid image width in IHDR");
+ error = 1;
+ }
+
+ if (height > PNG_UINT_31_MAX)
+ {
+ png_warning(png_ptr, "Invalid image height in IHDR");
+ error = 1;
+ }
+
+ if (width > (PNG_UINT_32_MAX
+ >> 3) /* 8-byte RGBA pixels */
+ - 48 /* bigrowbuf hack */
+ - 1 /* filter byte */
+ - 7*8 /* rounding of width to multiple of 8 pixels */
+ - 8) /* extra max_pixel_depth pad */
+ png_warning(png_ptr, "Width is too large for libpng to process pixels");
+
+ /* Check other values */
+ if (bit_depth != 1 && bit_depth != 2 && bit_depth != 4 &&
+ bit_depth != 8 && bit_depth != 16)
+ {
+ png_warning(png_ptr, "Invalid bit depth in IHDR");
+ error = 1;
+ }
+
+ if (color_type < 0 || color_type == 1 ||
+ color_type == 5 || color_type > 6)
+ {
+ png_warning(png_ptr, "Invalid color type in IHDR");
+ error = 1;
+ }
+
+ if (((color_type == PNG_COLOR_TYPE_PALETTE) && bit_depth > 8) ||
+ ((color_type == PNG_COLOR_TYPE_RGB ||
+ color_type == PNG_COLOR_TYPE_GRAY_ALPHA ||
+ color_type == PNG_COLOR_TYPE_RGB_ALPHA) && bit_depth < 8))
+ {
+ png_warning(png_ptr, "Invalid color type/bit depth combination in IHDR");
+ error = 1;
+ }
+
+ if (interlace_type >= PNG_INTERLACE_LAST)
+ {
+ png_warning(png_ptr, "Unknown interlace method in IHDR");
+ error = 1;
+ }
+
+ if (compression_type != PNG_COMPRESSION_TYPE_BASE)
+ {
+ png_warning(png_ptr, "Unknown compression method in IHDR");
+ error = 1;
+ }
+
+# ifdef PNG_MNG_FEATURES_SUPPORTED
+ /* Accept filter_method 64 (intrapixel differencing) only if
+ * 1. Libpng was compiled with PNG_MNG_FEATURES_SUPPORTED and
+ * 2. Libpng did not read a PNG signature (this filter_method is only
+ * used in PNG datastreams that are embedded in MNG datastreams) and
+ * 3. The application called png_permit_mng_features with a mask that
+ * included PNG_FLAG_MNG_FILTER_64 and
+ * 4. The filter_method is 64 and
+ * 5. The color_type is RGB or RGBA
+ */
+ if ((png_ptr->mode & PNG_HAVE_PNG_SIGNATURE) &&
+ png_ptr->mng_features_permitted)
+ png_warning(png_ptr, "MNG features are not allowed in a PNG datastream");
+
+ if (filter_type != PNG_FILTER_TYPE_BASE)
+ {
+ if (!((png_ptr->mng_features_permitted & PNG_FLAG_MNG_FILTER_64) &&
+ (filter_type == PNG_INTRAPIXEL_DIFFERENCING) &&
+ ((png_ptr->mode & PNG_HAVE_PNG_SIGNATURE) == 0) &&
+ (color_type == PNG_COLOR_TYPE_RGB ||
+ color_type == PNG_COLOR_TYPE_RGB_ALPHA)))
+ {
+ png_warning(png_ptr, "Unknown filter method in IHDR");
+ error = 1;
+ }
+
+ if (png_ptr->mode & PNG_HAVE_PNG_SIGNATURE)
+ {
+ png_warning(png_ptr, "Invalid filter method in IHDR");
+ error = 1;
+ }
+ }
+
+# else
+ if (filter_type != PNG_FILTER_TYPE_BASE)
+ {
+ png_warning(png_ptr, "Unknown filter method in IHDR");
+ error = 1;
+ }
+# endif
+
+ if (error == 1)
+ png_error(png_ptr, "Invalid IHDR data");
+}
+
+#if defined(PNG_sCAL_SUPPORTED) || defined(PNG_pCAL_SUPPORTED)
+/* ASCII to fp functions */
+/* Check an ASCII formated floating point value, see the more detailed
+ * comments in pngpriv.h
+ */
+/* The following is used internally to preserve the sticky flags */
+#define png_fp_add(state, flags) ((state) |= (flags))
+#define png_fp_set(state, value) ((state) = (value) | ((state) & PNG_FP_STICKY))
+
+int /* PRIVATE */
+png_check_fp_number(png_const_charp string, png_size_t size, int *statep,
+ png_size_tp whereami)
+{
+ int state = *statep;
+ png_size_t i = *whereami;
+
+ while (i < size)
+ {
+ int type;
+ /* First find the type of the next character */
+ switch (string[i])
+ {
+ case 43: type = PNG_FP_SAW_SIGN; break;
+ case 45: type = PNG_FP_SAW_SIGN + PNG_FP_NEGATIVE; break;
+ case 46: type = PNG_FP_SAW_DOT; break;
+ case 48: type = PNG_FP_SAW_DIGIT; break;
+ case 49: case 50: case 51: case 52:
+ case 53: case 54: case 55: case 56:
+ case 57: type = PNG_FP_SAW_DIGIT + PNG_FP_NONZERO; break;
+ case 69:
+ case 101: type = PNG_FP_SAW_E; break;
+ default: goto PNG_FP_End;
+ }
+
+ /* Now deal with this type according to the current
+ * state, the type is arranged to not overlap the
+ * bits of the PNG_FP_STATE.
+ */
+ switch ((state & PNG_FP_STATE) + (type & PNG_FP_SAW_ANY))
+ {
+ case PNG_FP_INTEGER + PNG_FP_SAW_SIGN:
+ if (state & PNG_FP_SAW_ANY)
+ goto PNG_FP_End; /* not a part of the number */
+
+ png_fp_add(state, type);
+ break;
+
+ case PNG_FP_INTEGER + PNG_FP_SAW_DOT:
+ /* Ok as trailer, ok as lead of fraction. */
+ if (state & PNG_FP_SAW_DOT) /* two dots */
+ goto PNG_FP_End;
+
+ else if (state & PNG_FP_SAW_DIGIT) /* trailing dot? */
+ png_fp_add(state, type);
+
+ else
+ png_fp_set(state, PNG_FP_FRACTION | type);
+
+ break;
+
+ case PNG_FP_INTEGER + PNG_FP_SAW_DIGIT:
+ if (state & PNG_FP_SAW_DOT) /* delayed fraction */
+ png_fp_set(state, PNG_FP_FRACTION | PNG_FP_SAW_DOT);
+
+ png_fp_add(state, type | PNG_FP_WAS_VALID);
+
+ break;
+
+ case PNG_FP_INTEGER + PNG_FP_SAW_E:
+ if ((state & PNG_FP_SAW_DIGIT) == 0)
+ goto PNG_FP_End;
+
+ png_fp_set(state, PNG_FP_EXPONENT);
+
+ break;
+
+ /* case PNG_FP_FRACTION + PNG_FP_SAW_SIGN:
+ goto PNG_FP_End; ** no sign in fraction */
+
+ /* case PNG_FP_FRACTION + PNG_FP_SAW_DOT:
+ goto PNG_FP_End; ** Because SAW_DOT is always set */
+
+ case PNG_FP_FRACTION + PNG_FP_SAW_DIGIT:
+ png_fp_add(state, type | PNG_FP_WAS_VALID);
+ break;
+
+ case PNG_FP_FRACTION + PNG_FP_SAW_E:
+ /* This is correct because the trailing '.' on an
+ * integer is handled above - so we can only get here
+ * with the sequence ".E" (with no preceding digits).
+ */
+ if ((state & PNG_FP_SAW_DIGIT) == 0)
+ goto PNG_FP_End;
+
+ png_fp_set(state, PNG_FP_EXPONENT);
+
+ break;
+
+ case PNG_FP_EXPONENT + PNG_FP_SAW_SIGN:
+ if (state & PNG_FP_SAW_ANY)
+ goto PNG_FP_End; /* not a part of the number */
+
+ png_fp_add(state, PNG_FP_SAW_SIGN);
+
+ break;
+
+ /* case PNG_FP_EXPONENT + PNG_FP_SAW_DOT:
+ goto PNG_FP_End; */
+
+ case PNG_FP_EXPONENT + PNG_FP_SAW_DIGIT:
+ png_fp_add(state, PNG_FP_SAW_DIGIT | PNG_FP_WAS_VALID);
+
+ break;
+
+ /* case PNG_FP_EXPONEXT + PNG_FP_SAW_E:
+ goto PNG_FP_End; */
+
+ default: goto PNG_FP_End; /* I.e. break 2 */
+ }
+
+ /* The character seems ok, continue. */
+ ++i;
+ }
+
+PNG_FP_End:
+ /* Here at the end, update the state and return the correct
+ * return code.
+ */
+ *statep = state;
+ *whereami = i;
+
+ return (state & PNG_FP_SAW_DIGIT) != 0;
+}
+
+
+/* The same but for a complete string. */
+int
+png_check_fp_string(png_const_charp string, png_size_t size)
+{
+ int state=0;
+ png_size_t char_index=0;
+
+ if (png_check_fp_number(string, size, &state, &char_index) &&
+ (char_index == size || string[char_index] == 0))
+ return state /* must be non-zero - see above */;
+
+ return 0; /* i.e. fail */
+}
+#endif /* pCAL or sCAL */
+
+#ifdef PNG_READ_sCAL_SUPPORTED
+# ifdef PNG_FLOATING_POINT_SUPPORTED
+/* Utility used below - a simple accurate power of ten from an integral
+ * exponent.
+ */
+static double
+png_pow10(int power)
+{
+ int recip = 0;
+ double d = 1;
+
+ /* Handle negative exponent with a reciprocal at the end because
+ * 10 is exact whereas .1 is inexact in base 2
+ */
+ if (power < 0)
+ {
+ if (power < DBL_MIN_10_EXP) return 0;
+ recip = 1, power = -power;
+ }
+
+ if (power > 0)
+ {
+ /* Decompose power bitwise. */
+ double mult = 10;
+ do
+ {
+ if (power & 1) d *= mult;
+ mult *= mult;
+ power >>= 1;
+ }
+ while (power > 0);
+
+ if (recip) d = 1/d;
+ }
+ /* else power is 0 and d is 1 */
+
+ return d;
+}
+
+/* Function to format a floating point value in ASCII with a given
+ * precision.
+ */
+void /* PRIVATE */
+png_ascii_from_fp(png_structp png_ptr, png_charp ascii, png_size_t size,
+ double fp, unsigned int precision)
+{
+ /* We use standard functions from math.h, but not printf because
+ * that would require stdio. The caller must supply a buffer of
+ * sufficient size or we will png_error. The tests on size and
+ * the space in ascii[] consumed are indicated below.
+ */
+ if (precision < 1)
+ precision = DBL_DIG;
+
+ /* Enforce the limit of the implementation precision too. */
+ if (precision > DBL_DIG+1)
+ precision = DBL_DIG+1;
+
+ /* Basic sanity checks */
+ if (size >= precision+5) /* See the requirements below. */
+ {
+ if (fp < 0)
+ {
+ fp = -fp;
+ *ascii++ = 45; /* '-' PLUS 1 TOTAL 1 */
+ --size;
+ }
+
+ if (fp >= DBL_MIN && fp <= DBL_MAX)
+ {
+ int exp_b10; /* A base 10 exponent */
+ double base; /* 10^exp_b10 */
+
+ /* First extract a base 10 exponent of the number,
+ * the calculation below rounds down when converting
+ * from base 2 to base 10 (multiply by log10(2) -
+ * 0.3010, but 77/256 is 0.3008, so exp_b10 needs to
+ * be increased. Note that the arithmetic shift
+ * performs a floor() unlike C arithmetic - using a
+ * C multiply would break the following for negative
+ * exponents.
+ */
+ (void)frexp(fp, &exp_b10); /* exponent to base 2 */
+
+ exp_b10 = (exp_b10 * 77) >> 8; /* <= exponent to base 10 */
+
+ /* Avoid underflow here. */
+ base = png_pow10(exp_b10); /* May underflow */
+
+ while (base < DBL_MIN || base < fp)
+ {
+ /* And this may overflow. */
+ double test = png_pow10(exp_b10+1);
+
+ if (test <= DBL_MAX)
+ ++exp_b10, base = test;
+
+ else
+ break;
+ }
+
+ /* Normalize fp and correct exp_b10, after this fp is in the
+ * range [.1,1) and exp_b10 is both the exponent and the digit
+ * *before* which the decimal point should be inserted
+ * (starting with 0 for the first digit). Note that this
+ * works even if 10^exp_b10 is out of range because of the
+ * test on DBL_MAX above.
+ */
+ fp /= base;
+ while (fp >= 1) fp /= 10, ++exp_b10;
+
+ /* Because of the code above fp may, at this point, be
+ * less than .1, this is ok because the code below can
+ * handle the leading zeros this generates, so no attempt
+ * is made to correct that here.
+ */
+
+ {
+ int czero, clead, cdigits;
+ char exponent[10];
+
+ /* Allow up to two leading zeros - this will not lengthen
+ * the number compared to using E-n.
+ */
+ if (exp_b10 < 0 && exp_b10 > -3) /* PLUS 3 TOTAL 4 */
+ {
+ czero = -exp_b10; /* PLUS 2 digits: TOTAL 3 */
+ exp_b10 = 0; /* Dot added below before first output. */
+ }
+ else
+ czero = 0; /* No zeros to add */
+
+ /* Generate the digit list, stripping trailing zeros and
+ * inserting a '.' before a digit if the exponent is 0.
+ */
+ clead = czero; /* Count of leading zeros */
+ cdigits = 0; /* Count of digits in list. */
+
+ do
+ {
+ double d;
+
+ fp *= 10;
+ /* Use modf here, not floor and subtract, so that
+ * the separation is done in one step. At the end
+ * of the loop don't break the number into parts so
+ * that the final digit is rounded.
+ */
+ if (cdigits+czero-clead+1 < (int)precision)
+ fp = modf(fp, &d);
+
+ else
+ {
+ d = floor(fp + .5);
+
+ if (d > 9)
+ {
+ /* Rounding up to 10, handle that here. */
+ if (czero > 0)
+ {
+ --czero, d = 1;
+ if (cdigits == 0) --clead;
+ }
+ else
+ {
+ while (cdigits > 0 && d > 9)
+ {
+ int ch = *--ascii;
+
+ if (exp_b10 != (-1))
+ ++exp_b10;
+
+ else if (ch == 46)
+ {
+ ch = *--ascii, ++size;
+ /* Advance exp_b10 to '1', so that the
+ * decimal point happens after the
+ * previous digit.
+ */
+ exp_b10 = 1;
+ }
+
+ --cdigits;
+ d = ch - 47; /* I.e. 1+(ch-48) */
+ }
+
+ /* Did we reach the beginning? If so adjust the
+ * exponent but take into account the leading
+ * decimal point.
+ */
+ if (d > 9) /* cdigits == 0 */
+ {
+ if (exp_b10 == (-1))
+ {
+ /* Leading decimal point (plus zeros?), if
+ * we lose the decimal point here it must
+ * be reentered below.
+ */
+ int ch = *--ascii;
+
+ if (ch == 46)
+ ++size, exp_b10 = 1;
+
+ /* Else lost a leading zero, so 'exp_b10' is
+ * still ok at (-1)
+ */
+ }
+ else
+ ++exp_b10;
+
+ /* In all cases we output a '1' */
+ d = 1;
+ }
+ }
+ }
+ fp = 0; /* Guarantees termination below. */
+ }
+
+ if (d == 0)
+ {
+ ++czero;
+ if (cdigits == 0) ++clead;
+ }
+ else
+ {
+ /* Included embedded zeros in the digit count. */
+ cdigits += czero - clead;
+ clead = 0;
+
+ while (czero > 0)
+ {
+ /* exp_b10 == (-1) means we just output the decimal
+ * place - after the DP don't adjust 'exp_b10' any
+ * more!
+ */
+ if (exp_b10 != (-1))
+ {
+ if (exp_b10 == 0) *ascii++ = 46, --size;
+ /* PLUS 1: TOTAL 4 */
+ --exp_b10;
+ }
+ *ascii++ = 48, --czero;
+ }
+
+ if (exp_b10 != (-1))
+ {
+ if (exp_b10 == 0) *ascii++ = 46, --size; /* counted
+ above */
+ --exp_b10;
+ }
+ *ascii++ = (char)(48 + (int)d), ++cdigits;
+ }
+ }
+ while (cdigits+czero-clead < (int)precision && fp > DBL_MIN);
+
+ /* The total output count (max) is now 4+precision */
+
+ /* Check for an exponent, if we don't need one we are
+ * done and just need to terminate the string. At
+ * this point exp_b10==(-1) is effectively if flag - it got
+ * to '-1' because of the decrement after outputing
+ * the decimal point above (the exponent required is
+ * *not* -1!)
+ */
+ if (exp_b10 >= (-1) && exp_b10 <= 2)
+ {
+ /* The following only happens if we didn't output the
+ * leading zeros above for negative exponent, so this
+ * doest add to the digit requirement. Note that the
+ * two zeros here can only be output if the two leading
+ * zeros were *not* output, so this doesn't increase
+ * the output count.
+ */
+ while (--exp_b10 >= 0) *ascii++ = 48;
+
+ *ascii = 0;
+
+ /* Total buffer requirement (including the '\0') is
+ * 5+precision - see check at the start.
+ */
+ return;
+ }
+
+ /* Here if an exponent is required, adjust size for
+ * the digits we output but did not count. The total
+ * digit output here so far is at most 1+precision - no
+ * decimal point and no leading or trailing zeros have
+ * been output.
+ */
+ size -= cdigits;
+
+ *ascii++ = 69, --size; /* 'E': PLUS 1 TOTAL 2+precision */
+
+ /* The following use of an unsigned temporary avoids ambiguities in
+ * the signed arithmetic on exp_b10 and permits GCC at least to do
+ * better optimization.
+ */
+ {
+ unsigned int uexp_b10;
+
+ if (exp_b10 < 0)
+ {
+ *ascii++ = 45, --size; /* '-': PLUS 1 TOTAL 3+precision */
+ uexp_b10 = -exp_b10;
+ }
+
+ else
+ uexp_b10 = exp_b10;
+
+ cdigits = 0;
+
+ while (uexp_b10 > 0)
+ {
+ exponent[cdigits++] = (char)(48 + uexp_b10 % 10);
+ uexp_b10 /= 10;
+ }
+ }
+
+ /* Need another size check here for the exponent digits, so
+ * this need not be considered above.
+ */
+ if ((int)size > cdigits)
+ {
+ while (cdigits > 0) *ascii++ = exponent[--cdigits];
+
+ *ascii = 0;
+
+ return;
+ }
+ }
+ }
+ else if (!(fp >= DBL_MIN))
+ {
+ *ascii++ = 48; /* '0' */
+ *ascii = 0;
+ return;
+ }
+ else
+ {
+ *ascii++ = 105; /* 'i' */
+ *ascii++ = 110; /* 'n' */
+ *ascii++ = 102; /* 'f' */
+ *ascii = 0;
+ return;
+ }
+ }
+
+ /* Here on buffer too small. */
+ png_error(png_ptr, "ASCII conversion buffer too small");
+}
+
+# endif /* FLOATING_POINT */
+
+# ifdef PNG_FIXED_POINT_SUPPORTED
+/* Function to format a fixed point value in ASCII.
+ */
+void /* PRIVATE */
+png_ascii_from_fixed(png_structp png_ptr, png_charp ascii, png_size_t size,
+ png_fixed_point fp)
+{
+ /* Require space for 10 decimal digits, a decimal point, a minus sign and a
+ * trailing \0, 13 characters:
+ */
+ if (size > 12)
+ {
+ png_uint_32 num;
+
+ /* Avoid overflow here on the minimum integer. */
+ if (fp < 0)
+ *ascii++ = 45, --size, num = -fp;
+ else
+ num = fp;
+
+ if (num <= 0x80000000) /* else overflowed */
+ {
+ unsigned int ndigits = 0, first = 16 /* flag value */;
+ char digits[10];
+
+ while (num)
+ {
+ /* Split the low digit off num: */
+ unsigned int tmp = num/10;
+ num -= tmp*10;
+ digits[ndigits++] = (char)(48 + num);
+ /* Record the first non-zero digit, note that this is a number
+ * starting at 1, it's not actually the array index.
+ */
+ if (first == 16 && num > 0)
+ first = ndigits;
+ num = tmp;
+ }
+
+ if (ndigits > 0)
+ {
+ while (ndigits > 5) *ascii++ = digits[--ndigits];
+ /* The remaining digits are fractional digits, ndigits is '5' or
+ * smaller at this point. It is certainly not zero. Check for a
+ * non-zero fractional digit:
+ */
+ if (first <= 5)
+ {
+ unsigned int i;
+ *ascii++ = 46; /* decimal point */
+ /* ndigits may be <5 for small numbers, output leading zeros
+ * then ndigits digits to first:
+ */
+ i = 5;
+ while (ndigits < i) *ascii++ = 48, --i;
+ while (ndigits >= first) *ascii++ = digits[--ndigits];
+ /* Don't output the trailing zeros! */
+ }
+ }
+ else
+ *ascii++ = 48;
+
+ /* And null terminate the string: */
+ *ascii = 0;
+ return;
+ }
+ }
+
+ /* Here on buffer too small. */
+ png_error(png_ptr, "ASCII conversion buffer too small");
+}
+# endif /* FIXED_POINT */
+#endif /* READ_SCAL */
+
+#if defined(PNG_FLOATING_POINT_SUPPORTED) && \
+ !defined(PNG_FIXED_POINT_MACRO_SUPPORTED)
+png_fixed_point
+png_fixed(png_structp png_ptr, double fp, png_const_charp text)
+{
+ double r = floor(100000 * fp + .5);
+
+ if (r > 2147483647. || r < -2147483648.)
+ png_fixed_error(png_ptr, text);
+
+ return (png_fixed_point)r;
+}
+#endif
+
+#if defined(PNG_READ_GAMMA_SUPPORTED) || \
+ defined(PNG_INCH_CONVERSIONS_SUPPORTED) || defined(PNG__READ_pHYs_SUPPORTED)
+/* muldiv functions */
+/* This API takes signed arguments and rounds the result to the nearest
+ * integer (or, for a fixed point number - the standard argument - to
+ * the nearest .00001). Overflow and divide by zero are signalled in
+ * the result, a boolean - true on success, false on overflow.
+ */
+int
+png_muldiv(png_fixed_point_p res, png_fixed_point a, png_int_32 times,
+ png_int_32 divisor)
+{
+ /* Return a * times / divisor, rounded. */
+ if (divisor != 0)
+ {
+ if (a == 0 || times == 0)
+ {
+ *res = 0;
+ return 1;
+ }
+ else
+ {
+#ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
+ double r = a;
+ r *= times;
+ r /= divisor;
+ r = floor(r+.5);
+
+ /* A png_fixed_point is a 32-bit integer. */
+ if (r <= 2147483647. && r >= -2147483648.)
+ {
+ *res = (png_fixed_point)r;
+ return 1;
+ }
+#else
+ int negative = 0;
+ png_uint_32 A, T, D;
+ png_uint_32 s16, s32, s00;
+
+ if (a < 0)
+ negative = 1, A = -a;
+ else
+ A = a;
+
+ if (times < 0)
+ negative = !negative, T = -times;
+ else
+ T = times;
+
+ if (divisor < 0)
+ negative = !negative, D = -divisor;
+ else
+ D = divisor;
+
+ /* Following can't overflow because the arguments only
+ * have 31 bits each, however the result may be 32 bits.
+ */
+ s16 = (A >> 16) * (T & 0xffff) +
+ (A & 0xffff) * (T >> 16);
+ /* Can't overflow because the a*times bit is only 30
+ * bits at most.
+ */
+ s32 = (A >> 16) * (T >> 16) + (s16 >> 16);
+ s00 = (A & 0xffff) * (T & 0xffff);
+
+ s16 = (s16 & 0xffff) << 16;
+ s00 += s16;
+
+ if (s00 < s16)
+ ++s32; /* carry */
+
+ if (s32 < D) /* else overflow */
+ {
+ /* s32.s00 is now the 64-bit product, do a standard
+ * division, we know that s32 < D, so the maximum
+ * required shift is 31.
+ */
+ int bitshift = 32;
+ png_fixed_point result = 0; /* NOTE: signed */
+
+ while (--bitshift >= 0)
+ {
+ png_uint_32 d32, d00;
+
+ if (bitshift > 0)
+ d32 = D >> (32-bitshift), d00 = D << bitshift;
+
+ else
+ d32 = 0, d00 = D;
+
+ if (s32 > d32)
+ {
+ if (s00 < d00) --s32; /* carry */
+ s32 -= d32, s00 -= d00, result += 1<<bitshift;
+ }
+
+ else
+ if (s32 == d32 && s00 >= d00)
+ s32 = 0, s00 -= d00, result += 1<<bitshift;
+ }
+
+ /* Handle the rounding. */
+ if (s00 >= (D >> 1))
+ ++result;
+
+ if (negative)
+ result = -result;
+
+ /* Check for overflow. */
+ if ((negative && result <= 0) || (!negative && result >= 0))
+ {
+ *res = result;
+ return 1;
+ }
+ }
+#endif
+ }
+ }
+
+ return 0;
+}
+#endif /* READ_GAMMA || INCH_CONVERSIONS */
+
+#if defined(PNG_READ_GAMMA_SUPPORTED) || defined(PNG_INCH_CONVERSIONS_SUPPORTED)
+/* The following is for when the caller doesn't much care about the
+ * result.
+ */
+png_fixed_point
+png_muldiv_warn(png_structp png_ptr, png_fixed_point a, png_int_32 times,
+ png_int_32 divisor)
+{
+ png_fixed_point result;
+
+ if (png_muldiv(&result, a, times, divisor))
+ return result;
+
+ png_warning(png_ptr, "fixed point overflow ignored");
+ return 0;
+}
+#endif
+
+#ifdef PNG_READ_GAMMA_SUPPORTED /* more fixed point functions for gammma */
+/* Calculate a reciprocal, return 0 on div-by-zero or overflow. */
+png_fixed_point
+png_reciprocal(png_fixed_point a)
+{
+#ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
+ double r = floor(1E10/a+.5);
+
+ if (r <= 2147483647. && r >= -2147483648.)
+ return (png_fixed_point)r;
+#else
+ png_fixed_point res;
+
+ if (png_muldiv(&res, 100000, 100000, a))
+ return res;
+#endif
+
+ return 0; /* error/overflow */
+}
+
+/* A local convenience routine. */
+static png_fixed_point
+png_product2(png_fixed_point a, png_fixed_point b)
+{
+ /* The required result is 1/a * 1/b; the following preserves accuracy. */
+#ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
+ double r = a * 1E-5;
+ r *= b;
+ r = floor(r+.5);
+
+ if (r <= 2147483647. && r >= -2147483648.)
+ return (png_fixed_point)r;
+#else
+ png_fixed_point res;
+
+ if (png_muldiv(&res, a, b, 100000))
+ return res;
+#endif
+
+ return 0; /* overflow */
+}
+
+/* The inverse of the above. */
+png_fixed_point
+png_reciprocal2(png_fixed_point a, png_fixed_point b)
+{
+ /* The required result is 1/a * 1/b; the following preserves accuracy. */
+#ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
+ double r = 1E15/a;
+ r /= b;
+ r = floor(r+.5);
+
+ if (r <= 2147483647. && r >= -2147483648.)
+ return (png_fixed_point)r;
+#else
+ /* This may overflow because the range of png_fixed_point isn't symmetric,
+ * but this API is only used for the product of file and screen gamma so it
+ * doesn't matter that the smallest number it can produce is 1/21474, not
+ * 1/100000
+ */
+ png_fixed_point res = png_product2(a, b);
+
+ if (res != 0)
+ return png_reciprocal(res);
+#endif
+
+ return 0; /* overflow */
+}
+#endif /* READ_GAMMA */
+
+#ifdef PNG_CHECK_cHRM_SUPPORTED
+/* Added at libpng version 1.2.34 (Dec 8, 2008) and 1.4.0 (Jan 2,
+ * 2010: moved from pngset.c) */
+/*
+ * Multiply two 32-bit numbers, V1 and V2, using 32-bit
+ * arithmetic, to produce a 64-bit result in the HI/LO words.
+ *
+ * A B
+ * x C D
+ * ------
+ * AD || BD
+ * AC || CB || 0
+ *
+ * where A and B are the high and low 16-bit words of V1,
+ * C and D are the 16-bit words of V2, AD is the product of
+ * A and D, and X || Y is (X << 16) + Y.
+*/
+
+void /* PRIVATE */
+png_64bit_product (long v1, long v2, unsigned long *hi_product,
+ unsigned long *lo_product)
+{
+ int a, b, c, d;
+ long lo, hi, x, y;
+
+ a = (v1 >> 16) & 0xffff;
+ b = v1 & 0xffff;
+ c = (v2 >> 16) & 0xffff;
+ d = v2 & 0xffff;
+
+ lo = b * d; /* BD */
+ x = a * d + c * b; /* AD + CB */
+ y = ((lo >> 16) & 0xffff) + x;
+
+ lo = (lo & 0xffff) | ((y & 0xffff) << 16);
+ hi = (y >> 16) & 0xffff;
+
+ hi += a * c; /* AC */
+
+ *hi_product = (unsigned long)hi;
+ *lo_product = (unsigned long)lo;
+}
+#endif /* CHECK_cHRM */
+
+#ifdef PNG_READ_GAMMA_SUPPORTED /* gamma table code */
+#ifndef PNG_FLOATING_ARITHMETIC_SUPPORTED
+/* Fixed point gamma.
+ *
+ * To calculate gamma this code implements fast log() and exp() calls using only
+ * fixed point arithmetic. This code has sufficient precision for either 8-bit
+ * or 16-bit sample values.
+ *
+ * The tables used here were calculated using simple 'bc' programs, but C double
+ * precision floating point arithmetic would work fine. The programs are given
+ * at the head of each table.
+ *
+ * 8-bit log table
+ * This is a table of -log(value/255)/log(2) for 'value' in the range 128 to
+ * 255, so it's the base 2 logarithm of a normalized 8-bit floating point
+ * mantissa. The numbers are 32-bit fractions.
+ */
+static png_uint_32
+png_8bit_l2[128] =
+{
+# ifdef PNG_DO_BC
+ for (i=128;i<256;++i) { .5 - l(i/255)/l(2)*65536*65536; }
+# else
+ 4270715492U, 4222494797U, 4174646467U, 4127164793U, 4080044201U, 4033279239U,
+ 3986864580U, 3940795015U, 3895065449U, 3849670902U, 3804606499U, 3759867474U,
+ 3715449162U, 3671346997U, 3627556511U, 3584073329U, 3540893168U, 3498011834U,
+ 3455425220U, 3413129301U, 3371120137U, 3329393864U, 3287946700U, 3246774933U,
+ 3205874930U, 3165243125U, 3124876025U, 3084770202U, 3044922296U, 3005329011U,
+ 2965987113U, 2926893432U, 2888044853U, 2849438323U, 2811070844U, 2772939474U,
+ 2735041326U, 2697373562U, 2659933400U, 2622718104U, 2585724991U, 2548951424U,
+ 2512394810U, 2476052606U, 2439922311U, 2404001468U, 2368287663U, 2332778523U,
+ 2297471715U, 2262364947U, 2227455964U, 2192742551U, 2158222529U, 2123893754U,
+ 2089754119U, 2055801552U, 2022034013U, 1988449497U, 1955046031U, 1921821672U,
+ 1888774511U, 1855902668U, 1823204291U, 1790677560U, 1758320682U, 1726131893U,
+ 1694109454U, 1662251657U, 1630556815U, 1599023271U, 1567649391U, 1536433567U,
+ 1505374214U, 1474469770U, 1443718700U, 1413119487U, 1382670639U, 1352370686U,
+ 1322218179U, 1292211689U, 1262349810U, 1232631153U, 1203054352U, 1173618059U,
+ 1144320946U, 1115161701U, 1086139034U, 1057251672U, 1028498358U, 999877854U,
+ 971388940U, 943030410U, 914801076U, 886699767U, 858725327U, 830876614U,
+ 803152505U, 775551890U, 748073672U, 720716771U, 693480120U, 666362667U,
+ 639363374U, 612481215U, 585715177U, 559064263U, 532527486U, 506103872U,
+ 479792461U, 453592303U, 427502463U, 401522014U, 375650043U, 349885648U,
+ 324227938U, 298676034U, 273229066U, 247886176U, 222646516U, 197509248U,
+ 172473545U, 147538590U, 122703574U, 97967701U, 73330182U, 48790236U,
+ 24347096U, 0U
+# endif
+
+#if 0
+ /* The following are the values for 16-bit tables - these work fine for the
+ * 8-bit conversions but produce very slightly larger errors in the 16-bit
+ * log (about 1.2 as opposed to 0.7 absolute error in the final value). To
+ * use these all the shifts below must be adjusted appropriately.
+ */
+ 65166, 64430, 63700, 62976, 62257, 61543, 60835, 60132, 59434, 58741, 58054,
+ 57371, 56693, 56020, 55352, 54689, 54030, 53375, 52726, 52080, 51439, 50803,
+ 50170, 49542, 48918, 48298, 47682, 47070, 46462, 45858, 45257, 44661, 44068,
+ 43479, 42894, 42312, 41733, 41159, 40587, 40020, 39455, 38894, 38336, 37782,
+ 37230, 36682, 36137, 35595, 35057, 34521, 33988, 33459, 32932, 32408, 31887,
+ 31369, 30854, 30341, 29832, 29325, 28820, 28319, 27820, 27324, 26830, 26339,
+ 25850, 25364, 24880, 24399, 23920, 23444, 22970, 22499, 22029, 21562, 21098,
+ 20636, 20175, 19718, 19262, 18808, 18357, 17908, 17461, 17016, 16573, 16132,
+ 15694, 15257, 14822, 14390, 13959, 13530, 13103, 12678, 12255, 11834, 11415,
+ 10997, 10582, 10168, 9756, 9346, 8937, 8531, 8126, 7723, 7321, 6921, 6523,
+ 6127, 5732, 5339, 4947, 4557, 4169, 3782, 3397, 3014, 2632, 2251, 1872, 1495,
+ 1119, 744, 372
+#endif
+};
+
+PNG_STATIC png_int_32
+png_log8bit(unsigned int x)
+{
+ unsigned int lg2 = 0;
+ /* Each time 'x' is multiplied by 2, 1 must be subtracted off the final log,
+ * because the log is actually negate that means adding 1. The final
+ * returned value thus has the range 0 (for 255 input) to 7.994 (for 1
+ * input), return 7.99998 for the overflow (log 0) case - so the result is
+ * always at most 19 bits.
+ */
+ if ((x &= 0xff) == 0)
+ return 0xffffffff;
+
+ if ((x & 0xf0) == 0)
+ lg2 = 4, x <<= 4;
+
+ if ((x & 0xc0) == 0)
+ lg2 += 2, x <<= 2;
+
+ if ((x & 0x80) == 0)
+ lg2 += 1, x <<= 1;
+
+ /* result is at most 19 bits, so this cast is safe: */
+ return (png_int_32)((lg2 << 16) + ((png_8bit_l2[x-128]+32768)>>16));
+}
+
+/* The above gives exact (to 16 binary places) log2 values for 8-bit images,
+ * for 16-bit images we use the most significant 8 bits of the 16-bit value to
+ * get an approximation then multiply the approximation by a correction factor
+ * determined by the remaining up to 8 bits. This requires an additional step
+ * in the 16-bit case.
+ *
+ * We want log2(value/65535), we have log2(v'/255), where:
+ *
+ * value = v' * 256 + v''
+ * = v' * f
+ *
+ * So f is value/v', which is equal to (256+v''/v') since v' is in the range 128
+ * to 255 and v'' is in the range 0 to 255 f will be in the range 256 to less
+ * than 258. The final factor also needs to correct for the fact that our 8-bit
+ * value is scaled by 255, whereas the 16-bit values must be scaled by 65535.
+ *
+ * This gives a final formula using a calculated value 'x' which is value/v' and
+ * scaling by 65536 to match the above table:
+ *
+ * log2(x/257) * 65536
+ *
+ * Since these numbers are so close to '1' we can use simple linear
+ * interpolation between the two end values 256/257 (result -368.61) and 258/257
+ * (result 367.179). The values used below are scaled by a further 64 to give
+ * 16-bit precision in the interpolation:
+ *
+ * Start (256): -23591
+ * Zero (257): 0
+ * End (258): 23499
+ */
+PNG_STATIC png_int_32
+png_log16bit(png_uint_32 x)
+{
+ unsigned int lg2 = 0;
+
+ /* As above, but now the input has 16 bits. */
+ if ((x &= 0xffff) == 0)
+ return 0xffffffff;
+
+ if ((x & 0xff00) == 0)
+ lg2 = 8, x <<= 8;
+
+ if ((x & 0xf000) == 0)
+ lg2 += 4, x <<= 4;
+
+ if ((x & 0xc000) == 0)
+ lg2 += 2, x <<= 2;
+
+ if ((x & 0x8000) == 0)
+ lg2 += 1, x <<= 1;
+
+ /* Calculate the base logarithm from the top 8 bits as a 28-bit fractional
+ * value.
+ */
+ lg2 <<= 28;
+ lg2 += (png_8bit_l2[(x>>8)-128]+8) >> 4;
+
+ /* Now we need to interpolate the factor, this requires a division by the top
+ * 8 bits. Do this with maximum precision.
+ */
+ x = ((x << 16) + (x >> 9)) / (x >> 8);
+
+ /* Since we divided by the top 8 bits of 'x' there will be a '1' at 1<<24,
+ * the value at 1<<16 (ignoring this) will be 0 or 1; this gives us exactly
+ * 16 bits to interpolate to get the low bits of the result. Round the
+ * answer. Note that the end point values are scaled by 64 to retain overall
+ * precision and that 'lg2' is current scaled by an extra 12 bits, so adjust
+ * the overall scaling by 6-12. Round at every step.
+ */
+ x -= 1U << 24;
+
+ if (x <= 65536U) /* <= '257' */
+ lg2 += ((23591U * (65536U-x)) + (1U << (16+6-12-1))) >> (16+6-12);
+
+ else
+ lg2 -= ((23499U * (x-65536U)) + (1U << (16+6-12-1))) >> (16+6-12);
+
+ /* Safe, because the result can't have more than 20 bits: */
+ return (png_int_32)((lg2 + 2048) >> 12);
+}
+
+/* The 'exp()' case must invert the above, taking a 20-bit fixed point
+ * logarithmic value and returning a 16 or 8-bit number as appropriate. In
+ * each case only the low 16 bits are relevant - the fraction - since the
+ * integer bits (the top 4) simply determine a shift.
+ *
+ * The worst case is the 16-bit distinction between 65535 and 65534, this
+ * requires perhaps spurious accuracy in the decoding of the logarithm to
+ * distinguish log2(65535/65534.5) - 10^-5 or 17 bits. There is little chance
+ * of getting this accuracy in practice.
+ *
+ * To deal with this the following exp() function works out the exponent of the
+ * frational part of the logarithm by using an accurate 32-bit value from the
+ * top four fractional bits then multiplying in the remaining bits.
+ */
+static png_uint_32
+png_32bit_exp[16] =
+{
+# ifdef PNG_DO_BC
+ for (i=0;i<16;++i) { .5 + e(-i/16*l(2))*2^32; }
+# else
+ /* NOTE: the first entry is deliberately set to the maximum 32-bit value. */
+ 4294967295U, 4112874773U, 3938502376U, 3771522796U, 3611622603U, 3458501653U,
+ 3311872529U, 3171459999U, 3037000500U, 2908241642U, 2784941738U, 2666869345U,
+ 2553802834U, 2445529972U, 2341847524U, 2242560872U
+# endif
+};
+
+/* Adjustment table; provided to explain the numbers in the code below. */
+#ifdef PNG_DO_BC
+for (i=11;i>=0;--i){ print i, " ", (1 - e(-(2^i)/65536*l(2))) * 2^(32-i), "\n"}
+ 11 44937.64284865548751208448
+ 10 45180.98734845585101160448
+ 9 45303.31936980687359311872
+ 8 45364.65110595323018870784
+ 7 45395.35850361789624614912
+ 6 45410.72259715102037508096
+ 5 45418.40724413220722311168
+ 4 45422.25021786898173001728
+ 3 45424.17186732298419044352
+ 2 45425.13273269940811464704
+ 1 45425.61317555035558641664
+ 0 45425.85339951654943850496
+#endif
+
+PNG_STATIC png_uint_32
+png_exp(png_fixed_point x)
+{
+ if (x > 0 && x <= 0xfffff) /* Else overflow or zero (underflow) */
+ {
+ /* Obtain a 4-bit approximation */
+ png_uint_32 e = png_32bit_exp[(x >> 12) & 0xf];
+
+ /* Incorporate the low 12 bits - these decrease the returned value by
+ * multiplying by a number less than 1 if the bit is set. The multiplier
+ * is determined by the above table and the shift. Notice that the values
+ * converge on 45426 and this is used to allow linear interpolation of the
+ * low bits.
+ */
+ if (x & 0x800)
+ e -= (((e >> 16) * 44938U) + 16U) >> 5;
+
+ if (x & 0x400)
+ e -= (((e >> 16) * 45181U) + 32U) >> 6;
+
+ if (x & 0x200)
+ e -= (((e >> 16) * 45303U) + 64U) >> 7;
+
+ if (x & 0x100)
+ e -= (((e >> 16) * 45365U) + 128U) >> 8;
+
+ if (x & 0x080)
+ e -= (((e >> 16) * 45395U) + 256U) >> 9;
+
+ if (x & 0x040)
+ e -= (((e >> 16) * 45410U) + 512U) >> 10;
+
+ /* And handle the low 6 bits in a single block. */
+ e -= (((e >> 16) * 355U * (x & 0x3fU)) + 256U) >> 9;
+
+ /* Handle the upper bits of x. */
+ e >>= x >> 16;
+ return e;
+ }
+
+ /* Check for overflow */
+ if (x <= 0)
+ return png_32bit_exp[0];
+
+ /* Else underflow */
+ return 0;
+}
+
+PNG_STATIC png_byte
+png_exp8bit(png_fixed_point lg2)
+{
+ /* Get a 32-bit value: */
+ png_uint_32 x = png_exp(lg2);
+
+ /* Convert the 32-bit value to 0..255 by multiplying by 256-1, note that the
+ * second, rounding, step can't overflow because of the first, subtraction,
+ * step.
+ */
+ x -= x >> 8;
+ return (png_byte)((x + 0x7fffffU) >> 24);
+}
+
+PNG_STATIC png_uint_16
+png_exp16bit(png_fixed_point lg2)
+{
+ /* Get a 32-bit value: */
+ png_uint_32 x = png_exp(lg2);
+
+ /* Convert the 32-bit value to 0..65535 by multiplying by 65536-1: */
+ x -= x >> 16;
+ return (png_uint_16)((x + 32767U) >> 16);
+}
+#endif /* FLOATING_ARITHMETIC */
+
+png_byte
+png_gamma_8bit_correct(unsigned int value, png_fixed_point gamma_val)
+{
+ if (value > 0 && value < 255)
+ {
+# ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
+ double r = floor(255*pow(value/255.,gamma_val*.00001)+.5);
+ return (png_byte)r;
+# else
+ png_int_32 lg2 = png_log8bit(value);
+ png_fixed_point res;
+
+ if (png_muldiv(&res, gamma_val, lg2, PNG_FP_1))
+ return png_exp8bit(res);
+
+ /* Overflow. */
+ value = 0;
+# endif
+ }
+
+ return (png_byte)value;
+}
+
+png_uint_16
+png_gamma_16bit_correct(unsigned int value, png_fixed_point gamma_val)
+{
+ if (value > 0 && value < 65535)
+ {
+# ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
+ double r = floor(65535*pow(value/65535.,gamma_val*.00001)+.5);
+ return (png_uint_16)r;
+# else
+ png_int_32 lg2 = png_log16bit(value);
+ png_fixed_point res;
+
+ if (png_muldiv(&res, gamma_val, lg2, PNG_FP_1))
+ return png_exp16bit(res);
+
+ /* Overflow. */
+ value = 0;
+# endif
+ }
+
+ return (png_uint_16)value;
+}
+
+/* This does the right thing based on the bit_depth field of the
+ * png_struct, interpreting values as 8-bit or 16-bit. While the result
+ * is nominally a 16-bit value if bit depth is 8 then the result is
+ * 8-bit (as are the arguments.)
+ */
+png_uint_16 /* PRIVATE */
+png_gamma_correct(png_structp png_ptr, unsigned int value,
+ png_fixed_point gamma_val)
+{
+ if (png_ptr->bit_depth == 8)
+ return png_gamma_8bit_correct(value, gamma_val);
+
+ else
+ return png_gamma_16bit_correct(value, gamma_val);
+}
+
+/* This is the shared test on whether a gamma value is 'significant' - whether
+ * it is worth doing gamma correction.
+ */
+int /* PRIVATE */
+png_gamma_significant(png_fixed_point gamma_val)
+{
+ return gamma_val < PNG_FP_1 - PNG_GAMMA_THRESHOLD_FIXED ||
+ gamma_val > PNG_FP_1 + PNG_GAMMA_THRESHOLD_FIXED;
+}
+
+/* Internal function to build a single 16-bit table - the table consists of
+ * 'num' 256-entry subtables, where 'num' is determined by 'shift' - the amount
+ * to shift the input values right (or 16-number_of_signifiant_bits).
+ *
+ * The caller is responsible for ensuring that the table gets cleaned up on
+ * png_error (i.e. if one of the mallocs below fails) - i.e. the *table argument
+ * should be somewhere that will be cleaned.
+ */
+static void
+png_build_16bit_table(png_structp png_ptr, png_uint_16pp *ptable,
+ PNG_CONST unsigned int shift, PNG_CONST png_fixed_point gamma_val)
+{
+ /* Various values derived from 'shift': */
+ PNG_CONST unsigned int num = 1U << (8U - shift);
+ PNG_CONST unsigned int max = (1U << (16U - shift))-1U;
+ PNG_CONST unsigned int max_by_2 = 1U << (15U-shift);
+ unsigned int i;
+
+ png_uint_16pp table = *ptable =
+ (png_uint_16pp)png_calloc(png_ptr, num * png_sizeof(png_uint_16p));
+
+ for (i = 0; i < num; i++)
+ {
+ png_uint_16p sub_table = table[i] =
+ (png_uint_16p)png_malloc(png_ptr, 256 * png_sizeof(png_uint_16));
+
+ /* The 'threshold' test is repeated here because it can arise for one of
+ * the 16-bit tables even if the others don't hit it.
+ */
+ if (png_gamma_significant(gamma_val))
+ {
+ /* The old code would overflow at the end and this would cause the
+ * 'pow' function to return a result >1, resulting in an
+ * arithmetic error. This code follows the spec exactly; ig is
+ * the recovered input sample, it always has 8-16 bits.
+ *
+ * We want input * 65535/max, rounded, the arithmetic fits in 32
+ * bits (unsigned) so long as max <= 32767.
+ */
+ unsigned int j;
+ for (j = 0; j < 256; j++)
+ {
+ png_uint_32 ig = (j << (8-shift)) + i;
+# ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
+ /* Inline the 'max' scaling operation: */
+ double d = floor(65535*pow(ig/(double)max, gamma_val*.00001)+.5);
+ sub_table[j] = (png_uint_16)d;
+# else
+ if (shift)
+ ig = (ig * 65535U + max_by_2)/max;
+
+ sub_table[j] = png_gamma_16bit_correct(ig, gamma_val);
+# endif
+ }
+ }
+ else
+ {
+ /* We must still build a table, but do it the fast way. */
+ unsigned int j;
+
+ for (j = 0; j < 256; j++)
+ {
+ png_uint_32 ig = (j << (8-shift)) + i;
+
+ if (shift)
+ ig = (ig * 65535U + max_by_2)/max;
+
+ sub_table[j] = (png_uint_16)ig;
+ }
+ }
+ }
+}
+
+/* NOTE: this function expects the *inverse* of the overall gamma transformation
+ * required.
+ */
+static void
+png_build_16to8_table(png_structp png_ptr, png_uint_16pp *ptable,
+ PNG_CONST unsigned int shift, PNG_CONST png_fixed_point gamma_val)
+{
+ PNG_CONST unsigned int num = 1U << (8U - shift);
+ PNG_CONST unsigned int max = (1U << (16U - shift))-1U;
+ unsigned int i;
+ png_uint_32 last;
+
+ png_uint_16pp table = *ptable =
+ (png_uint_16pp)png_calloc(png_ptr, num * png_sizeof(png_uint_16p));
+
+ /* 'num' is the number of tables and also the number of low bits of the
+ * input 16-bit value used to select a table. Each table is itself indexed
+ * by the high 8 bits of the value.
+ */
+ for (i = 0; i < num; i++)
+ table[i] = (png_uint_16p)png_malloc(png_ptr,
+ 256 * png_sizeof(png_uint_16));
+
+ /* 'gamma_val' is set to the reciprocal of the value calculated above, so
+ * pow(out,g) is an *input* value. 'last' is the last input value set.
+ *
+ * In the loop 'i' is used to find output values. Since the output is
+ * 8-bit there are only 256 possible values. The tables are set up to
+ * select the closest possible output value for each input by finding
+ * the input value at the boundary between each pair of output values
+ * and filling the table up to that boundary with the lower output
+ * value.
+ *
+ * The boundary values are 0.5,1.5..253.5,254.5. Since these are 9-bit
+ * values the code below uses a 16-bit value in i; the values start at
+ * 128.5 (for 0.5) and step by 257, for a total of 254 values (the last
+ * entries are filled with 255). Start i at 128 and fill all 'last'
+ * table entries <= 'max'
+ */
+ last = 0;
+ for (i = 0; i < 255; ++i) /* 8-bit output value */
+ {
+ /* Find the corresponding maximum input value */
+ png_uint_16 out = (png_uint_16)(i * 257U); /* 16-bit output value */
+
+ /* Find the boundary value in 16 bits: */
+ png_uint_32 bound = png_gamma_16bit_correct(out+128U, gamma_val);
+
+ /* Adjust (round) to (16-shift) bits: */
+ bound = (bound * max + 32768U)/65535U + 1U;
+
+ while (last < bound)
+ {
+ table[last & (0xffU >> shift)][last >> (8U - shift)] = out;
+ last++;
+ }
+ }
+
+ /* And fill in the final entries. */
+ while (last < (num << 8))
+ {
+ table[last & (0xff >> shift)][last >> (8U - shift)] = 65535U;
+ last++;
+ }
+}
+
+/* Build a single 8-bit table: same as the 16-bit case but much simpler (and
+ * typically much faster). Note that libpng currently does no sBIT processing
+ * (apparently contrary to the spec) so a 256-entry table is always generated.
+ */
+static void
+png_build_8bit_table(png_structp png_ptr, png_bytepp ptable,
+ PNG_CONST png_fixed_point gamma_val)
+{
+ unsigned int i;
+ png_bytep table = *ptable = (png_bytep)png_malloc(png_ptr, 256);
+
+ if (png_gamma_significant(gamma_val)) for (i=0; i<256; i++)
+ table[i] = png_gamma_8bit_correct(i, gamma_val);
+
+ else for (i=0; i<256; ++i)
+ table[i] = (png_byte)i;
+}
+
+/* Used from png_read_destroy and below to release the memory used by the gamma
+ * tables.
+ */
+void /* PRIVATE */
+png_destroy_gamma_table(png_structp png_ptr)
+{
+ png_free(png_ptr, png_ptr->gamma_table);
+ png_ptr->gamma_table = NULL;
+
+ if (png_ptr->gamma_16_table != NULL)
+ {
+ int i;
+ int istop = (1 << (8 - png_ptr->gamma_shift));
+ for (i = 0; i < istop; i++)
+ {
+ png_free(png_ptr, png_ptr->gamma_16_table[i]);
+ }
+ png_free(png_ptr, png_ptr->gamma_16_table);
+ png_ptr->gamma_16_table = NULL;
+ }
+
+#if defined(PNG_READ_BACKGROUND_SUPPORTED) || \
+ defined(PNG_READ_ALPHA_MODE_SUPPORTED) || \
+ defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
+ png_free(png_ptr, png_ptr->gamma_from_1);
+ png_ptr->gamma_from_1 = NULL;
+ png_free(png_ptr, png_ptr->gamma_to_1);
+ png_ptr->gamma_to_1 = NULL;
+
+ if (png_ptr->gamma_16_from_1 != NULL)
+ {
+ int i;
+ int istop = (1 << (8 - png_ptr->gamma_shift));
+ for (i = 0; i < istop; i++)
+ {
+ png_free(png_ptr, png_ptr->gamma_16_from_1[i]);
+ }
+ png_free(png_ptr, png_ptr->gamma_16_from_1);
+ png_ptr->gamma_16_from_1 = NULL;
+ }
+ if (png_ptr->gamma_16_to_1 != NULL)
+ {
+ int i;
+ int istop = (1 << (8 - png_ptr->gamma_shift));
+ for (i = 0; i < istop; i++)
+ {
+ png_free(png_ptr, png_ptr->gamma_16_to_1[i]);
+ }
+ png_free(png_ptr, png_ptr->gamma_16_to_1);
+ png_ptr->gamma_16_to_1 = NULL;
+ }
+#endif /* READ_BACKGROUND || READ_ALPHA_MODE || RGB_TO_GRAY */
+}
+
+/* We build the 8- or 16-bit gamma tables here. Note that for 16-bit
+ * tables, we don't make a full table if we are reducing to 8-bit in
+ * the future. Note also how the gamma_16 tables are segmented so that
+ * we don't need to allocate > 64K chunks for a full 16-bit table.
+ */
+void /* PRIVATE */
+png_build_gamma_table(png_structp png_ptr, int bit_depth)
+{
+ png_debug(1, "in png_build_gamma_table");
+
+ /* Remove any existing table; this copes with multiple calls to
+ * png_read_update_info. The warning is because building the gamma tables
+ * multiple times is a performance hit - it's harmless but the ability to call
+ * png_read_update_info() multiple times is new in 1.5.6 so it seems sensible
+ * to warn if the app introduces such a hit.
+ */
+ if (png_ptr->gamma_table != NULL || png_ptr->gamma_16_table != NULL)
+ {
+ png_warning(png_ptr, "gamma table being rebuilt");
+ png_destroy_gamma_table(png_ptr);
+ }
+
+ if (bit_depth <= 8)
+ {
+ png_build_8bit_table(png_ptr, &png_ptr->gamma_table,
+ png_ptr->screen_gamma > 0 ? png_reciprocal2(png_ptr->gamma,
+ png_ptr->screen_gamma) : PNG_FP_1);
+
+#if defined(PNG_READ_BACKGROUND_SUPPORTED) || \
+ defined(PNG_READ_ALPHA_MODE_SUPPORTED) || \
+ defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
+ if (png_ptr->transformations & (PNG_COMPOSE | PNG_RGB_TO_GRAY))
+ {
+ png_build_8bit_table(png_ptr, &png_ptr->gamma_to_1,
+ png_reciprocal(png_ptr->gamma));
+
+ png_build_8bit_table(png_ptr, &png_ptr->gamma_from_1,
+ png_ptr->screen_gamma > 0 ? png_reciprocal(png_ptr->screen_gamma) :
+ png_ptr->gamma/* Probably doing rgb_to_gray */);
+ }
+#endif /* READ_BACKGROUND || READ_ALPHA_MODE || RGB_TO_GRAY */
+ }
+ else
+ {
+ png_byte shift, sig_bit;
+
+ if (png_ptr->color_type & PNG_COLOR_MASK_COLOR)
+ {
+ sig_bit = png_ptr->sig_bit.red;
+
+ if (png_ptr->sig_bit.green > sig_bit)
+ sig_bit = png_ptr->sig_bit.green;
+
+ if (png_ptr->sig_bit.blue > sig_bit)
+ sig_bit = png_ptr->sig_bit.blue;
+ }
+ else
+ sig_bit = png_ptr->sig_bit.gray;
+
+ /* 16-bit gamma code uses this equation:
+ *
+ * ov = table[(iv & 0xff) >> gamma_shift][iv >> 8]
+ *
+ * Where 'iv' is the input color value and 'ov' is the output value -
+ * pow(iv, gamma).
+ *
+ * Thus the gamma table consists of up to 256 256-entry tables. The table
+ * is selected by the (8-gamma_shift) most significant of the low 8 bits of
+ * the color value then indexed by the upper 8 bits:
+ *
+ * table[low bits][high 8 bits]
+ *
+ * So the table 'n' corresponds to all those 'iv' of:
+ *
+ * <all high 8-bit values><n << gamma_shift>..<(n+1 << gamma_shift)-1>
+ *
+ */
+ if (sig_bit > 0 && sig_bit < 16U)
+ shift = (png_byte)(16U - sig_bit); /* shift == insignificant bits */
+
+ else
+ shift = 0; /* keep all 16 bits */
+
+ if (png_ptr->transformations & (PNG_16_TO_8 | PNG_SCALE_16_TO_8))
+ {
+ /* PNG_MAX_GAMMA_8 is the number of bits to keep - effectively
+ * the significant bits in the *input* when the output will
+ * eventually be 8 bits. By default it is 11.
+ */
+ if (shift < (16U - PNG_MAX_GAMMA_8))
+ shift = (16U - PNG_MAX_GAMMA_8);
+ }
+
+ if (shift > 8U)
+ shift = 8U; /* Guarantees at least one table! */
+
+ png_ptr->gamma_shift = shift;
+
+#ifdef PNG_16BIT_SUPPORTED
+ /* NOTE: prior to 1.5.4 this test used to include PNG_BACKGROUND (now
+ * PNG_COMPOSE). This effectively smashed the background calculation for
+ * 16-bit output because the 8-bit table assumes the result will be reduced
+ * to 8 bits.
+ */
+ if (png_ptr->transformations & (PNG_16_TO_8 | PNG_SCALE_16_TO_8))
+#endif
+ png_build_16to8_table(png_ptr, &png_ptr->gamma_16_table, shift,
+ png_ptr->screen_gamma > 0 ? png_product2(png_ptr->gamma,
+ png_ptr->screen_gamma) : PNG_FP_1);
+
+#ifdef PNG_16BIT_SUPPORTED
+ else
+ png_build_16bit_table(png_ptr, &png_ptr->gamma_16_table, shift,
+ png_ptr->screen_gamma > 0 ? png_reciprocal2(png_ptr->gamma,
+ png_ptr->screen_gamma) : PNG_FP_1);
+#endif
+
+#if defined(PNG_READ_BACKGROUND_SUPPORTED) || \
+ defined(PNG_READ_ALPHA_MODE_SUPPORTED) || \
+ defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
+ if (png_ptr->transformations & (PNG_COMPOSE | PNG_RGB_TO_GRAY))
+ {
+ png_build_16bit_table(png_ptr, &png_ptr->gamma_16_to_1, shift,
+ png_reciprocal(png_ptr->gamma));
+
+ /* Notice that the '16 from 1' table should be full precision, however
+ * the lookup on this table still uses gamma_shift, so it can't be.
+ * TODO: fix this.
+ */
+ png_build_16bit_table(png_ptr, &png_ptr->gamma_16_from_1, shift,
+ png_ptr->screen_gamma > 0 ? png_reciprocal(png_ptr->screen_gamma) :
+ png_ptr->gamma/* Probably doing rgb_to_gray */);
+ }
+#endif /* READ_BACKGROUND || READ_ALPHA_MODE || RGB_TO_GRAY */
+ }
projects / wxWidgets.git / blobdiff