# _memmove() Author: Kees J. Bot 2 Jan 1994
# void *_memmove(void *s1, const void *s2, size_t n)
# Copy a chunk of memory. Handle overlap.
.intel_syntax
.globl __memmove, __memcpy
.text
.align 16
__memmove:
push ebp
mov ebp, esp
push esi
push edi
mov edi, [ebp+8] # String s1
mov esi, [ebp+12] # String s2
mov ecx, [ebp+16] # Length
mov eax, edi
sub eax, esi
cmp eax, ecx
jb downwards # if (s2 - s1) < n then copy downwards
__memcpy:
cld # Clear direction bit: upwards
cmp ecx, 16
jb upbyte # Don't bother being smart with short arrays
mov eax, esi
or eax, edi
testb al, 1
jnz upbyte # Bit 0 set, use byte copy
testb al, 2
jnz upword # Bit 1 set, use word copy
uplword:
shrd eax, ecx, 2 # Save low 2 bits of ecx in eax
shr ecx, 2
rep movsd # Copy longwords.
shld ecx, eax, 2 # Restore excess count
upword:
shr ecx, 1
rep movsw # Copy words
adc ecx, ecx # One more byte?
upbyte:
rep movsb # Copy bytes
done:
mov eax, [ebp+8] # Absolutely noone cares about this value
pop edi
pop esi
pop ebp
ret
# Handle bad overlap by copying downwards, don't bother to do word copies.
downwards:
std # Set direction bit: downwards
lea esi, [esi+ecx-1]
lea edi, [edi+ecx-1]
rep movsb # Copy bytes
cld
jmp done