AMD Typewriter x86 사용자 설명서

22007E/0—November 1999

;_ulldiv divides two unsigned 64-bit integers, and returns
;

the quotient.

;
;INPUT: 

[ESP+8]:[ESP+4]   dividend

; 

[ESP+16]:[ESP+12] divisor

;
;OUTPUT:

EDX:EAX     quotient of division

;
;DESTROYS: EAX,ECX,EDX,EFlags
_ulldiv PROC
PUSH    EBX 

;save EBX as per calling convention

MOV     ECX, [ESP+20] 

;divisor_hi

MOV     EBX, [ESP+16] 

;divisor_lo

MOV     EDX, [ESP+12] 

;dividend_hi

MOV     EAX, [ESP+8] 

;dividend_lo

TEST    ECX, ECX 

;divisor > 2^32–1?

JNZ     $big_divisor 

;yes, divisor > 32^32–1

CMP     EDX, EBX 

;only one division needed? (ECX = 0)

JAE     $two_divs 

;need two divisions

DIV     EBX 

;EAX = quotient_lo

MOV     EDX, ECX 

;EDX = quotient_hi = 0 (quotient in
; EDX:EAX)

POP     EBX 

;restore EBX as per calling convention

RET 

;done, return to caller

$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 

;quotient_hi in EAX

XCHG    EAX, ECX 

;ECX = quotient_hi, EAX = dividend_lo

DIV     EBX 

;EAX = quotient_lo

MOV     EDX, ECX 

;EDX = quotient_hi (quotient in EDX:EAX)

POP     EBX 

;restore EBX as per calling convention

RET 

;done, return to caller

$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
SHRD    EAX, EDX, CL  ; such that divisor is 
SHR     EDX, CL 

;  less than 2^32 (i.e. fits in EBX)

ROL     EDI, 1 

;restore original divisor_hi

DIV     EBX 

;compute quotient

MOV     EBX, [ESP+12]  ;dividend_lo