Source code of Windows XP (NT5)
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title llmul - long multiply routine;***;llmul.asm - long multiply routine;; Copyright (c) 1985-1994, Microsoft Corporation. All rights reserved.;;Purpose:; Defines long multiply routine; Both signed and unsigned routines are the same, since multiply's; work out the same in 2's complement; creates the following routine:; __allmul;;*******************************************************************************
.xlistinclude cruntime.incinclude mm.inc.list
;***;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;;Exceptions:;;*******************************************************************************
CODESEG
_allmul PROC NEAR
A EQU [esp + 4] ; stack address of aB 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 aB2 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
end
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