AMD Typewriter x86 사용자 설명서

Efficient 64-Bit Integer Arithmetic

22007E/0—November 1999

AMD Athlon™ Processor x86 Code Optimization

Example 4 (Left shift):

;shift operand in EDX:EAX left, shift count in ECX (count
;

applied modulo 64)

SHLD EDX, EAX, CL ;first apply shift count
SHL EAX, CL ; mod 32 to EDX:EAX
TEST ECX, 32 ;need to shift by another 32?
JZ $lshift_done ;no, done
MOV EDX, EAX ;left shift EDX:EAX
XOR EAX, EAX ; by 32 bits

$lshift_done:

Example 5 (Right shift):

SHRD EAX, EDX, CL ;first apply shift count
SHR EDX, CL ; mod 32 to EDX:EAX
TEST ECX, 32 ;need to shift by another 32?
JZ $rshift_done ;no, done
MOV EAX, EDX ;left shift EDX:EAX
XOR EDX, EDX ; by 32 bits

$rshift_done:

Example 6 (Multiplication):

;_llmul computes the low-order half of the product of its
;

arguments, two 64-bit integers

;
;INPUT:

[ESP+8]:[ESP+4] multiplicand

;

[ESP+16]:[ESP+12] multiplier

;
;OUTPUT: EDX:EAX (multiplicand * multiplier) % 2^64
;
;DESTROYS: EAX,ECX,EDX,EFlags

_llmul PROC
MOV EDX, [ESP+8]

;multiplicand_hi

MOV ECX, [ESP+16]

;multiplier_hi

OR EDX, ECX

;one operand >= 2^32?

MOV EDX, [ESP+12]

;multiplier_lo

MOV EAX, [ESP+4]

;multiplicand_lo

JNZ $twomul

;yes, need two multiplies

MUL EDX

;multiplicand_lo * multiplier_lo

RET

;done, return to caller

$twomul:
IMUL EDX, [ESP+8] ;p3_lo = multiplicand_hi*multiplier_lo
IMUL ECX, EAX

;p2_lo = multiplier_hi*multiplicand_lo

ADD ECX, EDX

; p2_lo + p3_lo

MUL DWORD PTR [ESP+12] ;p1=multiplicand_lo*multiplier_lo
ADD EDX, ECX

;p1+p2lo+p3_lo = result in EDX:EAX

RET

;done, return to caller

_llmul ENDP