src/zlib/inffast.c

/* inffast.c -- fast decoding
 * Copyright (C) 1995-2003 Mark Adler
 * For conditions of distribution and use, see copyright notice in zlib.h
 */

#include "zutil.h"
#include "inftrees.h"
#include "inflate.h"
#include "inffast.h"

#ifndef ASMINF

/* Allow machine dependent optimization for post-increment or pre-increment.
   Based on testing to date,
   Pre-increment preferred for:
   - PowerPC G3 (Adler)
   - MIPS R5000 (Randers-Pehrson)
   Post-increment preferred for:
   - none
   No measurable difference:
   - Pentium III (Anderson)
   - 68060 (Nikl)
 */
#ifdef POSTINC
#  define OFF 0
#  define PUP(a) *(a)++
#else
#  define OFF 1
#  define PUP(a) *++(a)
#endif

/*
   Decode literal, length, and distance codes and write out the resulting
   literal and match bytes until either not enough input or output is
   available, an end-of-block is encountered, or a data error is encountered.
   When large enough input and output buffers are supplied to inflate(), for
   example, a 16K input buffer and a 64K output buffer, more than 95% of the
   inflate execution time is spent in this routine.

   Entry assumptions:

        state->mode == LEN
        strm->avail_in >= 6
        strm->avail_out >= 258
        start >= strm->avail_out
        state->bits < 8

   On return, state->mode is one of:

        LEN -- ran out of enough output space or enough available input
        TYPE -- reached end of block code, inflate() to interpret next block
        BAD -- error in block data

   Notes:

    - The maximum input bits used by a length/distance pair is 15 bits for the
      length code, 5 bits for the length extra, 15 bits for the distance code,
      and 13 bits for the distance extra.  This totals 48 bits, or six bytes.
      Therefore if strm->avail_in >= 6, then there is enough input to avoid
      checking for available input while decoding.

    - The maximum bytes that a single length/distance pair can output is 258
      bytes, which is the maximum length that can be coded.  inflate_fast()
      requires strm->avail_out >= 258 for each loop to avoid checking for
      output space.
 */
void inflate_fast(strm, start)
z_streamp strm;
unsigned start;         /* inflate()'s starting value for strm->avail_out */
{
    struct inflate_state FAR *state;
    unsigned char FAR *in;      /* local strm->next_in */
    unsigned char FAR *last;    /* while in < last, enough input available */
    unsigned char FAR *out;     /* local strm->next_out */
    unsigned char FAR *beg;     /* inflate()'s initial strm->next_out */
    unsigned char FAR *end;     /* while out < end, enough space available */
    unsigned wsize;             /* window size or zero if not using window */
    unsigned whave;             /* valid bytes in the window */
    unsigned write;             /* window write index */
    unsigned char FAR *window;  /* allocated sliding window, if wsize != 0 */
    unsigned long hold;         /* local strm->hold */
    unsigned bits;              /* local strm->bits */
    code const FAR *lcode;      /* local strm->lencode */
    code const FAR *dcode;      /* local strm->distcode */
    unsigned lmask;             /* mask for first level of length codes */
    unsigned dmask;             /* mask for first level of distance codes */
    code this;                  /* retrieved table entry */
    unsigned op;                /* code bits, operation, extra bits, or */
                                /*  window position, window bytes to copy */
    unsigned len;               /* match length, unused bytes */
    unsigned dist;              /* match distance */
    unsigned char FAR *from;    /* where to copy match from */

    /* copy state to local variables */
    state = (struct inflate_state FAR *)strm->state;
    in = strm->next_in - OFF;
    last = in + (strm->avail_in - 5);
    out = strm->next_out - OFF;
    beg = out - (start - strm->avail_out);
    end = out + (strm->avail_out - 257);
    wsize = state->wsize;
    whave = state->whave;
    write = state->write;
    window = state->window;
    hold = state->hold;
    bits = state->bits;
    lcode = state->lencode;
    dcode = state->distcode;
    lmask = (1U << state->lenbits) - 1;
    dmask = (1U << state->distbits) - 1;

    /* decode literals and length/distances until end-of-block or not enough
       input data or output space */
    do {
        if (bits < 15) {
            hold += (unsigned long)(PUP(in)) << bits;
            bits += 8;
            hold += (unsigned long)(PUP(in)) << bits;
            bits += 8;
        }
        this = lcode[hold & lmask];
      dolen:
        op = (unsigned)(this.bits);
        hold >>= op;
        bits -= op;
        op = (unsigned)(this.op);
        if (op == 0) {                          /* literal */
            Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ?
                    "inflate:         literal '%c'\n" :
                    "inflate:         literal 0x%02x\n", this.val));
            PUP(out) = (unsigned char)(this.val);
        }
        else if (op & 16) {                     /* length base */
            len = (unsigned)(this.val);
            op &= 15;                           /* number of extra bits */
            if (op) {
                if (bits < op) {
                    hold += (unsigned long)(PUP(in)) << bits;
                    bits += 8;
                }
                len += (unsigned)hold & ((1U << op) - 1);
                hold >>= op;
                bits -= op;
            }
            Tracevv((stderr, "inflate:         length %u\n", len));
            if (bits < 15) {
                hold += (unsigned long)(PUP(in)) << bits;
                bits += 8;
                hold += (unsigned long)(PUP(in)) << bits;
                bits += 8;
            }
            this = dcode[hold & dmask];
          dodist:
            op = (unsigned)(this.bits);
            hold >>= op;
            bits -= op;
            op = (unsigned)(this.op);
            if (op & 16) {                      /* distance base */
                dist = (unsigned)(this.val);
                op &= 15;                       /* number of extra bits */
                if (bits < op) {
                    hold += (unsigned long)(PUP(in)) << bits;
                    bits += 8;
                    if (bits < op) {
                        hold += (unsigned long)(PUP(in)) << bits;
                        bits += 8;
                    }
                }
                dist += (unsigned)hold & ((1U << op) - 1);
                hold >>= op;
                bits -= op;
                Tracevv((stderr, "inflate:         distance %u\n", dist));
                op = (unsigned)(out - beg);     /* max distance in output */
                if (dist > op) {                /* see if copy from window */
                    op = dist - op;             /* distance back in window */
                    if (op > whave) {
                        strm->msg = (char *)"invalid distance too far back";
                        state->mode = BAD;
                        break;
                    }
                    from = window - OFF;
                    if (write == 0) {           /* very common case */
                        from += wsize - op;
                        if (op < len) {         /* some from window */
                            len -= op;
                            do {
                                PUP(out) = PUP(from);
                            } while (--op);
                            from = out - dist;  /* rest from output */
                        }
                    }
                    else if (write < op) {      /* wrap around window */
                        from += wsize + write - op;
                        op -= write;
                        if (op < len) {         /* some from end of window */
                            len -= op;
                            do {
                                PUP(out) = PUP(from);
                            } while (--op);
                            from = window - OFF;
                            if (write < len) {  /* some from start of window */
                                op = write;
                                len -= op;
                                do {
                                    PUP(out) = PUP(from);
                                } while (--op);
                                from = out - dist;      /* rest from output */
                            }
                        }
                    }
                    else {                      /* contiguous in window */
                        from += write - op;
                        if (op < len) {         /* some from window */
                            len -= op;
                            do {
                                PUP(out) = PUP(from);
                            } while (--op);
                            from = out - dist;  /* rest from output */
                        }
                    }
                    while (len > 2) {
                        PUP(out) = PUP(from);
                        PUP(out) = PUP(from);
                        PUP(out) = PUP(from);
                        len -= 3;
                    }
                    if (len) {
                        PUP(out) = PUP(from);
                        if (len > 1)
                            PUP(out) = PUP(from);
                    }
                }
                else {
                    from = out - dist;          /* copy direct from output */
                    do {                        /* minimum length is three */
                        PUP(out) = PUP(from);
                        PUP(out) = PUP(from);
                        PUP(out) = PUP(from);
                        len -= 3;
                    } while (len > 2);
                    if (len) {
                        PUP(out) = PUP(from);
                        if (len > 1)
                            PUP(out) = PUP(from);
                    }
                }
            }
            else if ((op & 64) == 0) {          /* 2nd level distance code */
                this = dcode[this.val + (hold & ((1U << op) - 1))];
                goto dodist;
            }
            else {
                strm->msg = (char *)"invalid distance code";
                state->mode = BAD;
                break;
            }
        }
        else if ((op & 64) == 0) {              /* 2nd level length code */
            this = lcode[this.val + (hold & ((1U << op) - 1))];
            goto dolen;
        }
        else if (op & 32) {                     /* end-of-block */
            Tracevv((stderr, "inflate:         end of block\n"));
            state->mode = TYPE;
            break;
        }
        else {
            strm->msg = (char *)"invalid literal/length code";
            state->mode = BAD;
            break;
        }
    } while (in < last && out < end);

    /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
    len = bits >> 3;
    in -= len;
    bits -= len << 3;
    hold &= (1U << bits) - 1;

    /* update state and return */
    strm->next_in = in + OFF;
    strm->next_out = out + OFF;
    strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
    strm->avail_out = (unsigned)(out < end ?
                                 257 + (end - out) : 257 - (out - end));
    state->hold = hold;
    state->bits = bits;
    return;
}

/*
   inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
   - Using bit fields for code structure
   - Different op definition to avoid & for extra bits (do & for table bits)
   - Three separate decoding do-loops for direct, window, and write == 0
   - Special case for distance > 1 copies to do overlapped load and store copy
   - Explicit branch predictions (based on measured branch probabilities)
   - Deferring match copy and interspersed it with decoding subsequent codes
   - Swapping literal/length else
   - Swapping window/direct else
   - Larger unrolled copy loops (three is about right)
   - Moving len -= 3 statement into middle of loop
 */

#endif /* !ASMINF */
Commit	Line	Data
	1	/* inffast.c -- fast decoding
	2	* Copyright (C) 1995-2003 Mark Adler
	3	* For conditions of distribution and use, see copyright notice in zlib.h
	4	*/
	5
	6	#include "zutil.h"
	7	#include "inftrees.h"
	8	#include "inflate.h"
	9	#include "inffast.h"
	10
	11	#ifndef ASMINF
	12
	13	/* Allow machine dependent optimization for post-increment or pre-increment.
	14	Based on testing to date,
	15	Pre-increment preferred for:
	16	- PowerPC G3 (Adler)
	17	- MIPS R5000 (Randers-Pehrson)
	18	Post-increment preferred for:
	19	- none
	20	No measurable difference:
	21	- Pentium III (Anderson)
	22	- 68060 (Nikl)
	23	*/
	24	#ifdef POSTINC
	25	# define OFF 0
	26	# define PUP(a) *(a)++
	27	#else
	28	# define OFF 1
	29	# define PUP(a) *++(a)
	30	#endif
	31
	32	/*
	33	Decode literal, length, and distance codes and write out the resulting
	34	literal and match bytes until either not enough input or output is
	35	available, an end-of-block is encountered, or a data error is encountered.
	36	When large enough input and output buffers are supplied to inflate(), for
	37	example, a 16K input buffer and a 64K output buffer, more than 95% of the
	38	inflate execution time is spent in this routine.
	39
	40	Entry assumptions:
	41
	42	state->mode == LEN
	43	strm->avail_in >= 6
	44	strm->avail_out >= 258
	45	start >= strm->avail_out
	46	state->bits < 8
	47
	48	On return, state->mode is one of:
	49
	50	LEN -- ran out of enough output space or enough available input
	51	TYPE -- reached end of block code, inflate() to interpret next block
	52	BAD -- error in block data
	53
	54	Notes:
	55
	56	- The maximum input bits used by a length/distance pair is 15 bits for the
	57	length code, 5 bits for the length extra, 15 bits for the distance code,
	58	and 13 bits for the distance extra. This totals 48 bits, or six bytes.
	59	Therefore if strm->avail_in >= 6, then there is enough input to avoid
	60	checking for available input while decoding.
	61
	62	- The maximum bytes that a single length/distance pair can output is 258
	63	bytes, which is the maximum length that can be coded. inflate_fast()
	64	requires strm->avail_out >= 258 for each loop to avoid checking for
	65	output space.
	66	*/
	67	void inflate_fast(strm, start)
	68	z_streamp strm;
	69	unsigned start; /* inflate()'s starting value for strm->avail_out */
	70	{
	71	struct inflate_state FAR *state;
	72	unsigned char FAR in; / local strm->next_in */
	73	unsigned char FAR last; / while in < last, enough input available */
	74	unsigned char FAR out; / local strm->next_out */
	75	unsigned char FAR beg; / inflate()'s initial strm->next_out */
	76	unsigned char FAR end; / while out < end, enough space available */
	77	unsigned wsize; /* window size or zero if not using window */
	78	unsigned whave; /* valid bytes in the window */
	79	unsigned write; /* window write index */
	80	unsigned char FAR window; / allocated sliding window, if wsize != 0 */
	81	unsigned long hold; /* local strm->hold */
	82	unsigned bits; /* local strm->bits */
	83	code const FAR lcode; / local strm->lencode */
	84	code const FAR dcode; / local strm->distcode */
	85	unsigned lmask; /* mask for first level of length codes */
	86	unsigned dmask; /* mask for first level of distance codes */
	87	code this; /* retrieved table entry */
	88	unsigned op; /* code bits, operation, extra bits, or */
	89	/* window position, window bytes to copy */
	90	unsigned len; /* match length, unused bytes */
	91	unsigned dist; /* match distance */
	92	unsigned char FAR from; / where to copy match from */
	93
	94	/* copy state to local variables */
	95	state = (struct inflate_state FAR *)strm->state;
	96	in = strm->next_in - OFF;
	97	last = in + (strm->avail_in - 5);
	98	out = strm->next_out - OFF;
	99	beg = out - (start - strm->avail_out);
	100	end = out + (strm->avail_out - 257);
	101	wsize = state->wsize;
	102	whave = state->whave;
	103	write = state->write;
	104	window = state->window;
	105	hold = state->hold;
	106	bits = state->bits;
	107	lcode = state->lencode;
	108	dcode = state->distcode;
	109	lmask = (1U << state->lenbits) - 1;
	110	dmask = (1U << state->distbits) - 1;
	111
	112	/* decode literals and length/distances until end-of-block or not enough
	113	input data or output space */
	114	do {
	115	if (bits < 15) {
	116	hold += (unsigned long)(PUP(in)) << bits;
	117	bits += 8;
	118	hold += (unsigned long)(PUP(in)) << bits;
	119	bits += 8;
	120	}
	121	this = lcode[hold & lmask];
	122	dolen:
	123	op = (unsigned)(this.bits);
	124	hold >>= op;
	125	bits -= op;
	126	op = (unsigned)(this.op);
	127	if (op == 0) { /* literal */
	128	Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ?
	129	"inflate: literal '%c'\n" :
	130	"inflate: literal 0x%02x\n", this.val));
	131	PUP(out) = (unsigned char)(this.val);
	132	}
	133	else if (op & 16) { /* length base */
	134	len = (unsigned)(this.val);
	135	op &= 15; /* number of extra bits */
	136	if (op) {
	137	if (bits < op) {
	138	hold += (unsigned long)(PUP(in)) << bits;
	139	bits += 8;
	140	}
	141	len += (unsigned)hold & ((1U << op) - 1);
	142	hold >>= op;
	143	bits -= op;
	144	}
	145	Tracevv((stderr, "inflate: length %u\n", len));
	146	if (bits < 15) {
	147	hold += (unsigned long)(PUP(in)) << bits;
	148	bits += 8;
	149	hold += (unsigned long)(PUP(in)) << bits;
	150	bits += 8;
	151	}
	152	this = dcode[hold & dmask];
	153	dodist:
	154	op = (unsigned)(this.bits);
	155	hold >>= op;
	156	bits -= op;
	157	op = (unsigned)(this.op);
	158	if (op & 16) { /* distance base */
	159	dist = (unsigned)(this.val);
	160	op &= 15; /* number of extra bits */
	161	if (bits < op) {
	162	hold += (unsigned long)(PUP(in)) << bits;
	163	bits += 8;
	164	if (bits < op) {
	165	hold += (unsigned long)(PUP(in)) << bits;
	166	bits += 8;
	167	}
	168	}
	169	dist += (unsigned)hold & ((1U << op) - 1);
	170	hold >>= op;
	171	bits -= op;
	172	Tracevv((stderr, "inflate: distance %u\n", dist));
	173	op = (unsigned)(out - beg); /* max distance in output */
	174	if (dist > op) { /* see if copy from window */
	175	op = dist - op; /* distance back in window */
	176	if (op > whave) {
	177	strm->msg = (char *)"invalid distance too far back";
	178	state->mode = BAD;
	179	break;
	180	}
	181	from = window - OFF;
	182	if (write == 0) { /* very common case */
	183	from += wsize - op;
	184	if (op < len) { /* some from window */
	185	len -= op;
	186	do {
	187	PUP(out) = PUP(from);
	188	} while (--op);
	189	from = out - dist; /* rest from output */
	190	}
	191	}
	192	else if (write < op) { /* wrap around window */
	193	from += wsize + write - op;
	194	op -= write;
	195	if (op < len) { /* some from end of window */
	196	len -= op;
	197	do {
	198	PUP(out) = PUP(from);
	199	} while (--op);
	200	from = window - OFF;
	201	if (write < len) { /* some from start of window */
	202	op = write;
	203	len -= op;
	204	do {
	205	PUP(out) = PUP(from);
	206	} while (--op);
	207	from = out - dist; /* rest from output */
	208	}
	209	}
	210	}
	211	else { /* contiguous in window */
	212	from += write - op;
	213	if (op < len) { /* some from window */
	214	len -= op;
	215	do {
	216	PUP(out) = PUP(from);
	217	} while (--op);
	218	from = out - dist; /* rest from output */
	219	}
	220	}
	221	while (len > 2) {
	222	PUP(out) = PUP(from);
	223	PUP(out) = PUP(from);
	224	PUP(out) = PUP(from);
	225	len -= 3;
	226	}
	227	if (len) {
	228	PUP(out) = PUP(from);
	229	if (len > 1)
	230	PUP(out) = PUP(from);
	231	}
	232	}
	233	else {
	234	from = out - dist; /* copy direct from output */
	235	do { /* minimum length is three */
	236	PUP(out) = PUP(from);
	237	PUP(out) = PUP(from);
	238	PUP(out) = PUP(from);
	239	len -= 3;
	240	} while (len > 2);
	241	if (len) {
	242	PUP(out) = PUP(from);
	243	if (len > 1)
	244	PUP(out) = PUP(from);
	245	}
	246	}
	247	}
	248	else if ((op & 64) == 0) { /* 2nd level distance code */
	249	this = dcode[this.val + (hold & ((1U << op) - 1))];
	250	goto dodist;
	251	}
	252	else {
	253	strm->msg = (char *)"invalid distance code";
	254	state->mode = BAD;
	255	break;
	256	}
	257	}
	258	else if ((op & 64) == 0) { /* 2nd level length code */
	259	this = lcode[this.val + (hold & ((1U << op) - 1))];
	260	goto dolen;
	261	}
	262	else if (op & 32) { /* end-of-block */
	263	Tracevv((stderr, "inflate: end of block\n"));
	264	state->mode = TYPE;
	265	break;
	266	}
	267	else {
	268	strm->msg = (char *)"invalid literal/length code";
	269	state->mode = BAD;
	270	break;
	271	}
	272	} while (in < last && out < end);
	273
	274	/* return unused bytes (on entry, bits < 8, so in won't go too far back) */
	275	len = bits >> 3;
	276	in -= len;
	277	bits -= len << 3;
	278	hold &= (1U << bits) - 1;
	279
	280	/* update state and return */
	281	strm->next_in = in + OFF;
	282	strm->next_out = out + OFF;
	283	strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
	284	strm->avail_out = (unsigned)(out < end ?
	285	257 + (end - out) : 257 - (out - end));
	286	state->hold = hold;
	287	state->bits = bits;
	288	return;
	289	}
	290
	291	/*
	292	inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
	293	- Using bit fields for code structure
	294	- Different op definition to avoid & for extra bits (do & for table bits)
	295	- Three separate decoding do-loops for direct, window, and write == 0
	296	- Special case for distance > 1 copies to do overlapped load and store copy
	297	- Explicit branch predictions (based on measured branch probabilities)
	298	- Deferring match copy and interspersed it with decoding subsequent codes
	299	- Swapping literal/length else
	300	- Swapping window/direct else
	301	- Larger unrolled copy loops (three is about right)
	302	- Moving len -= 3 statement into middle of loop
	303	*/
	304
	305	#endif /* !ASMINF */