;-----------------------------------------------------------------------------
; llmul.asm - long multiply routine
; Adapted from Visual Studio C runtime library
; Portions Copyright (c) Microsoft Corporation. All rights reserved.
;-----------------------------------------------------------------------------
.386
_TEXT segment use32 para public 'CODE'
public __allmul
LOWORD equ [0]
HIWORD equ [4]
;
; llmul - long multiply routine
;
; Purpose:
; Does a long multiply (same for signed/unsigned)
; Parameters are not changed.
;
; Entry:
; Parameters are passed on the stack:
; 1st pushed: multiplier (QWORD)
; 2nd pushed: multiplicand (QWORD)
;
; Exit:
; EDX:EAX - product of multiplier and multiplicand
; NOTE: parameters are removed from the stack
;
; Uses:
; ECX
;
__allmul proc near
assume cs:_TEXT
A EQU [esp + 4] ; stack address of a
B EQU [esp + 12] ; stack address of b
;
; AHI, BHI : upper 32 bits of A and B
; ALO, BLO : lower 32 bits of A and B
;
; ALO * BLO
; ALO * BHI
; + BLO * AHI
; ---------------------
;
mov eax,HIWORD(A)
mov ecx,HIWORD(B)
or ecx,eax ;test for both hiwords zero.
mov ecx,LOWORD(B)
jnz short hard ;both are zero, just mult ALO and BLO
mov eax,LOWORD(A)
mul ecx
ret 16 ; callee restores the stack
hard:
push ebx
; must redefine A and B since esp has been altered
A2 EQU [esp + 8] ; stack address of a
B2 EQU [esp + 16] ; stack address of b
mul ecx ;eax has AHI, ecx has BLO, so AHI * BLO
mov ebx,eax ;save result
mov eax,LOWORD(A2)
mul dword ptr HIWORD(B2) ;ALO * BHI
add ebx,eax ;ebx = ((ALO * BHI) + (AHI * BLO))
mov eax,LOWORD(A2) ;ecx = BLO
mul ecx ;so edx:eax = ALO*BLO
add edx,ebx ;now edx has all the LO*HI stuff
pop ebx
ret 16 ; callee restores the stack
__allmul endp
_TEXT ends
end
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