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;; Licensed to the .NET Foundation under one or more agreements.
;; The .NET Foundation licenses this file to you under the MIT license.
;; See the LICENSE file in the project root for more information.
.586
.xmm
.model flat
option casemap:none
EXTERN _IsProcessorFeaturePresent@4 : PROC
PF_XMMI64_INSTRUCTIONS_AVAILABLE equ 10
.data
canUseSSE2 db 0
.code
_memclr_for_gc@8 proc public
; x86 version
; we get the following parameters
; ecx = destination address
; edx = size to clear
push ebx
push edi
xor eax, eax
; load destination
mov edi,[esp+8+4]
; load size
mov ebx,[esp+8+8]
; check alignment of destination
test edi,3
jnz alignDest
alignDone:
; now destination is dword aligned
; compute number of bytes to clear non-temporally
; we wish to clear the first 8k or so with rep stos,
; anything above that non-temporally
xor edx,edx
cmp ebx,8*1024
jbe noNonTempClear
; can we use SSE2 instructions?
cmp canUseSSE2,0
js noNonTempClear
jz computeCanUseSSE2
computeNonTempClear:
; compute the number of bytes above 8k
; and round down to a multiple of 64
mov edx,ebx
sub edx,8*1024
and edx,not 63
; compute remaining size to clear temporally
sub ebx,edx
noNonTempClear:
; do the temporal clear
mov ecx,ebx
shr ecx,2
rep stosd
; do the non-temporal clear
test edx,edx
jne nonTempClearLoop
nonTempClearDone:
; clear any remaining bytes
mov ecx,ebx
and ecx,3
rep stosb
pop edi
pop ebx
ret 8
; this is the infrequent case, hence out of line
nonTempClearLoop:
movnti [edi+ 0],eax
movnti [edi+ 4],eax
movnti [edi+ 8],eax
movnti [edi+12],eax
movnti [edi+16],eax
movnti [edi+20],eax
movnti [edi+24],eax
movnti [edi+28],eax
movnti [edi+32],eax
movnti [edi+36],eax
movnti [edi+40],eax
movnti [edi+44],eax
movnti [edi+48],eax
movnti [edi+52],eax
movnti [edi+56],eax
movnti [edi+60],eax
add edi,64
sub edx,64
ja nonTempClearLoop
jmp nonTempClearDone
alignDest:
test ebx,ebx
je alignDone
alignLoop:
mov [edi],al
add edi,1
sub ebx,1
jz alignDone
test edi,3
jnz alignLoop
jmp alignDone
computeCanUseSSE2:
; we are not using the sse2 register set,
; just sse2 instructions (movnti),
; thus we just ask the OS about the usability of the instructions
; OS bugs about saving/restoring registers like in early versions
; of Vista etc. in the WoW shouldn't matter
push PF_XMMI64_INSTRUCTIONS_AVAILABLE
call _IsProcessorFeaturePresent@4
mov ecx,eax
xor eax,eax ; reset eax to 0
test ecx,ecx
mov canUseSSE2,1
jne computeNonTempClear
mov canUseSSE2,-1
xor edx,edx
jmp noNonTempClear
_memclr_for_gc@8 endp
end
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