AMD 250 manual Bit Signed Remainder Computation, 176

Software Optimization Guide for AMD64 Processors 25112 Rev. 3.06 September 2005

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.

176 Integer Optimizations Chapter 8