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176 Integer Optimizations Chapter 8
25112 Rev. 3.06 September 2005
Software Optimization Guide for AMD64 Processors
mov eax, [esp+20] ; divisor_lo
sbb ecx, edx ; Subtract divisor * quot. from dividend.
sbb edx, edx ; (remainder < 0) ? 0xFFFFFFFF : 0
and eax, edx ; (remainder < 0) ? divisor_lo : 0
and edx, [esp+24] ; (remainder < 0) ? divisor_hi : 0
add eax, ebx ; remainder += (remainder < 0) ? divisor : 0
pop edi ; Restore EDI as per calling convention.
pop ebx ; Restore EBX as per calling convention.
ret ; Done, return to caller.
_ullrem ENDP
64-Bit Signed Remainder Computation
; _llrem divides two signed 64-bit numbers and returns the remainder.
;
; In: [ESP+8]:[ESP+4] = dividend
; [ESP+16]:[ESP+12] = divisor
;
; Out: EDX:EAX = remainder of division
;
; Destroys: EAX, ECX, EDX, EFlags
push ebx ; Save EBX as per calling convention.
push esi ; Save ESI as per calling convention.
push edi ; Save EDI as per calling convention.
mov ecx, [esp+28] ; divisor-hi
mov ebx, [esp+24] ; divisor-lo
mov edx, [esp+20] ; dividend-hi
mov eax, [esp+16] ; dividend-lo
mov esi, edx ; sign(remainder) == sign(dividend)
sar esi, 31 ; (remainder < 0) ? -1 : 0
mov edi, edx ; dividend-hi
sar edi, 31 ; (dividend < 0) ? -1 : 0
xor eax, edi ; If (dividend < 0),
xor edx, edi ; compute 1's complement of dividend.
sub eax, edi ; If (dividend < 0),
sbb edx, edi ; compute 2's complement of dividend.
mov edi, ecx ; divisor-hi
sar edi, 31 ; (divisor < 0) ? -1 : 0
xor ebx, edi ; If (divisor < 0),
xor ecx, edi ; compute 1's complement of divisor.
sub ebx, edi ; If (divisor < 0),
sbb ecx, edi ; compute 2's complement of divisor.
jnz sr_big_divisor ; divisor > 2^32 - 1
cmp edx, ebx ; Only one division needed (ECX = 0)?
jae sr_two_divs ; No, need two divisions.
div ebx ; EAX = quotient_lo
mov eax, edx ; EAX = remainder_lo
mov edx, ecx ; EDX = remainder_lo = 0
xor eax, esi ; If (remainder < 0),
xor edx, esi ; compute 1's complement of result.