src/png/pnggccrd.c

   1 /* pnggccrd.c was removed from libpng-1.2.20. */
   2
   3 /* This code snippet is for use by configure's compilation test. */
   4
   5 #if defined(PNG_ASSEMBLER_CODE_SUPPORTED) && \
   6     defined(PNG_MMX_CODE_SUPPORTED)
   7 int PNGAPI png_dummy_mmx_support(void);
   8
   9 static int _mmx_supported = 2; // 0: no MMX; 1: MMX supported; 2: not tested
  10
  11 int PNGAPI
  12 png_dummy_mmx_support(void) __attribute__((noinline));
  13
  14 int PNGAPI
  15 png_dummy_mmx_support(void)
  16 {
  17    int result;
  18 #if defined(PNG_MMX_CODE_SUPPORTED)  // superfluous, but what the heck
  19     __asm__ __volatile__ (
  20 #if defined(__x86_64__)
  21         "pushq %%rbx          \n\t"  // rbx gets clobbered by CPUID instruction
  22         "pushq %%rcx          \n\t"  // so does rcx...
  23         "pushq %%rdx          \n\t"  // ...and rdx (but rcx & rdx safe on Linux)
  24         "pushfq               \n\t"  // save Eflag to stack
  25         "popq %%rax           \n\t"  // get Eflag from stack into rax
  26         "movq %%rax, %%rcx    \n\t"  // make another copy of Eflag in rcx
  27         "xorl $0x200000, %%eax \n\t" // toggle ID bit in Eflag (i.e., bit 21)
  28         "pushq %%rax          \n\t"  // save modified Eflag back to stack
  29         "popfq                \n\t"  // restore modified value to Eflag reg
  30         "pushfq               \n\t"  // save Eflag to stack
  31         "popq %%rax           \n\t"  // get Eflag from stack
  32         "pushq %%rcx          \n\t"  // save original Eflag to stack
  33         "popfq                \n\t"  // restore original Eflag
  34 #else
  35         "pushl %%ebx          \n\t"  // ebx gets clobbered by CPUID instruction
  36         "pushl %%ecx          \n\t"  // so does ecx...
  37         "pushl %%edx          \n\t"  // ...and edx (but ecx & edx safe on Linux)
  38         "pushfl               \n\t"  // save Eflag to stack
  39         "popl %%eax           \n\t"  // get Eflag from stack into eax
  40         "movl %%eax, %%ecx    \n\t"  // make another copy of Eflag in ecx
  41         "xorl $0x200000, %%eax \n\t" // toggle ID bit in Eflag (i.e., bit 21)
  42         "pushl %%eax          \n\t"  // save modified Eflag back to stack
  43         "popfl                \n\t"  // restore modified value to Eflag reg
  44         "pushfl               \n\t"  // save Eflag to stack
  45         "popl %%eax           \n\t"  // get Eflag from stack
  46         "pushl %%ecx          \n\t"  // save original Eflag to stack
  47         "popfl                \n\t"  // restore original Eflag
  48 #endif
  49         "xorl %%ecx, %%eax    \n\t"  // compare new Eflag with original Eflag
  50         "jz 0f                \n\t"  // if same, CPUID instr. is not supported
  51
  52         "xorl %%eax, %%eax    \n\t"  // set eax to zero
  53 //      ".byte  0x0f, 0xa2    \n\t"  // CPUID instruction (two-byte opcode)
  54         "cpuid                \n\t"  // get the CPU identification info
  55         "cmpl $1, %%eax       \n\t"  // make sure eax return non-zero value
  56         "jl 0f                \n\t"  // if eax is zero, MMX is not supported
  57
  58         "xorl %%eax, %%eax    \n\t"  // set eax to zero and...
  59         "incl %%eax           \n\t"  // ...increment eax to 1.  This pair is
  60                                      // faster than the instruction "mov eax, 1"
  61         "cpuid                \n\t"  // get the CPU identification info again
  62         "andl $0x800000, %%edx \n\t" // mask out all bits but MMX bit (23)
  63         "cmpl $0, %%edx       \n\t"  // 0 = MMX not supported
  64         "jz 0f                \n\t"  // non-zero = yes, MMX IS supported
  65
  66         "movl $1, %%eax       \n\t"  // set return value to 1
  67         "jmp  1f              \n\t"  // DONE:  have MMX support
  68
  69     "0:                       \n\t"  // .NOT_SUPPORTED: target label for jump instructions
  70         "movl $0, %%eax       \n\t"  // set return value to 0
  71     "1:                       \n\t"  // .RETURN: target label for jump instructions
  72 #if defined(__x86_64__)
  73         "popq %%rdx           \n\t"  // restore rdx
  74         "popq %%rcx           \n\t"  // restore rcx
  75         "popq %%rbx           \n\t"  // restore rbx
  76 #else
  77         "popl %%edx           \n\t"  // restore edx
  78         "popl %%ecx           \n\t"  // restore ecx
  79         "popl %%ebx           \n\t"  // restore ebx
  80 #endif
  81
  82 //      "ret                  \n\t"  // DONE:  no MMX support
  83                                      // (fall through to standard C "ret")
  84
  85         : "=a" (result)              // output list
  86
  87         :                            // any variables used on input (none)
  88
  89                                      // no clobber list
  90 //      , "%ebx", "%ecx", "%edx"     // GRR:  we handle these manually
  91 //      , "memory"   // if write to a variable gcc thought was in a reg
  92 //      , "cc"       // "condition codes" (flag bits)
  93     );
  94     _mmx_supported = result;
  95 #else
  96     _mmx_supported = 0;
  97 #endif /* PNG_MMX_CODE_SUPPORTED */
  98
  99     return _mmx_supported;
 100 }
 101 #endif