x86_memcpy.asm

   1 bits 32
   2 section .text
   3 ;extern "C" int asm_memcpy
   4 ;  (unsigned char *dest, unsigned char *src, int len);
   5
   6 global asm_memcpy
   7
   8 times ($$-$) & 3 db 0
   9
  10 asm_memcpy:
  11
  12 pushad                  ; save registers
  13 mov edi,[esp+36]        ; get 1st argument
  14 mov esi,[esp+40]        ; ...2nd
  15 mov eax,[esp+44]        ; ...3rd
  16
  17 mov edx, eax
  18 shr eax, 2              ; figure out how many 4 byte chunks we have
  19 and edx, 3              ; also figure out slack
  20 test eax, eax           ; Do we have any big chunks?
  21 push edx
  22 jz .slack               ; If not, just do slack
  23
  24 mov ecx,eax
  25
  26 rep movsd               ; move 4 byte chunks
  27
  28 .slack:
  29 pop ecx
  30 rep movsb               ; move 1 byte slack
  31
  32 popad                   ; clean up
  33 ret
  34
  35 ; --------------------------------------
  36
  37 %ifdef NASM_STACK_NOEXEC
  38 section .note.GNU-stack noalloc noexec nowrite progbits
  39 %endif