AMD x86 manual Shr Edx

AMD Athlon™ Processor x86 Code Optimization 22007E/0 — November 1999

$r_two_divs:
MOV	ECX, EAX		;save dividend_lo in ECX
MOV	EAX, EDX		;get dividend_hi
XOR	EDX, EDX		;zero extend it into EDX:EAX
DIV	EBX		;EAX = quotient_hi, EDX = intermediate
			; remainder
MOV	EAX, ECX		;EAX = dividend_lo
DIV	EBX		;EAX = quotient_lo
MOV	EAX, EDX		;EAX = remainder_lo
XOR	EDX, EDX		;EDX = remainder_hi = 0
POP	EBX		;restore EBX as per calling convention
RET			;done, return to caller
$r_big_divisor:
PUSH	EDI			;save EDI as per calling convention
MOV	EDI, ECX			;save divisor_hi
SHR	EDX,	1		;shift both divisor and dividend right
RCR	EAX,	1		; by 1 bit
ROR	EDI,	1
RCR	EBX,	1
BSR	ECX,	ECX		;ECX = number of remaining shifts
SHRD	EBX,	EDI, CL		;scale down divisor and dividend such
SHRD	EAX,	EDX, CL		; that divisor is less than 2^32
SHR	EDX,	CL		;	(i.e. fits in EBX)
ROL	EDI,	1		;restore original divisor (EDI:ESI)
DIV	EBX			;compute quotient
MOV	EBX, [ESP+12]			;dividend lo-word
MOV	ECX, EAX			;save quotient
IMUL	EDI, EAX			;quotient * divisor hi-word (low only)
MUL	DWORD PTR [ESP+20] ;quotient * divisor lo-word
ADD	EDX, EDI			;EDX:EAX = quotient * divisor
SUB	EBX, EAX			;dividend_lo – (quot.*divisor)–lo
MOV	ECX, [ESP+16]			;dividend_hi
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)?
ADC	EDX, ECX			; 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

90 Efficient 64-Bit Integer Arithmetic