kolibrios-gitea/drivers/ddk/string/memset.S

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# memset() Author: Kees J. Bot
# 2 Jan 1994
# void *memset(void *s, int c, size_t n)
# Set a chunk of memory to the same byte value.
#
.intel_syntax
.global _memset
.text
.align 16
_memset:
push ebp
mov ebp, esp
push edi
mov edi, [8+ebp] # The string
movzx eax, byte ptr [12+ebp] # The fill byte
mov ecx, [16+ebp] # Length
cld
cmp ecx, 16
jb sbyte # Don't bother being smart with short arrays
test edi, 1
jnz sbyte # Bit 0 set, use byte store
test edi, 2
jnz sword # Bit 1 set, use word store
slword:
movb ah, al
mov edx, eax
sal edx, 16
or eax, edx # One byte to four bytes
shrd edx, ecx, 2 # Save low two bits of ecx in edx
shr ecx, 2
rep stosd # Store longwords.
shld ecx, edx, 2 # Restore low two bits
sword:
movb ah, al # One byte to two bytes
shr ecx, 1
rep stosw # Store words
adc ecx, ecx # One more byte?
sbyte:
rep stosb # Store bytes
done:
mov eax, [8+ebp] # Return some value you have no need for
pop edi
pop ebp
ret