99 lines
2.4 KiB
NASM
99 lines
2.4 KiB
NASM
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title llmul - long multiply routine
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;***
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;llmul.asm - long multiply routine
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;
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; Copyright (c) 1985-1994, Microsoft Corporation. All rights reserved.
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;
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;Purpose:
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; Defines long multiply routine
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; Both signed and unsigned routines are the same, since multiply's
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; work out the same in 2's complement
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; creates the following routine:
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; __allmul
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;
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;*******************************************************************************
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.xlist
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include cruntime.inc
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include mm.inc
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.list
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;***
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;llmul - long multiply routine
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;
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;Purpose:
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; Does a long multiply (same for signed/unsigned)
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; Parameters are not changed.
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;
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;Entry:
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; Parameters are passed on the stack:
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; 1st pushed: multiplier (QWORD)
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; 2nd pushed: multiplicand (QWORD)
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;
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;Exit:
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; EDX:EAX - product of multiplier and multiplicand
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; NOTE: parameters are removed from the stack
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;
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;Uses:
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; ECX
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;
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;Exceptions:
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;
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;*******************************************************************************
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CODESEG
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_allmul PROC NEAR
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A EQU [esp + 4] ; stack address of a
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B EQU [esp + 12] ; stack address of b
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;
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; AHI, BHI : upper 32 bits of A and B
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; ALO, BLO : lower 32 bits of A and B
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;
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; ALO * BLO
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; ALO * BHI
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; + BLO * AHI
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; ---------------------
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;
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mov eax,HIWORD(A)
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mov ecx,HIWORD(B)
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or ecx,eax ;test for both hiwords zero.
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mov ecx,LOWORD(B)
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jnz short hard ;both are zero, just mult ALO and BLO
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mov eax,LOWORD(A)
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mul ecx
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ret 16 ; callee restores the stack
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hard:
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push ebx
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; must redefine A and B since esp has been altered
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A2 EQU [esp + 8] ; stack address of a
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B2 EQU [esp + 16] ; stack address of b
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mul ecx ;eax has AHI, ecx has BLO, so AHI * BLO
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mov ebx,eax ;save result
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mov eax,LOWORD(A2)
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mul dword ptr HIWORD(B2) ;ALO * BHI
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add ebx,eax ;ebx = ((ALO * BHI) + (AHI * BLO))
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mov eax,LOWORD(A2) ;ecx = BLO
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mul ecx ;so edx:eax = ALO*BLO
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add edx,ebx ;now edx has all the LO*HI stuff
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pop ebx
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ret 16 ; callee restores the stack
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_allmul ENDP
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end
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