115 lines
2.1 KiB
NASM
115 lines
2.1 KiB
NASM
page ,132
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title lmul - long multiply routine
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;***
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;lmul.asm - long multiply routine
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;
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; Copyright (c) Microsoft Corporation. All rights reserved.
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;
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;Purpose:
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; Defines long multiply routines
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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 routines:
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; __aFlmul, __aFulmul (large, medium model)
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; __aNlmul, __aNulmul (small, compact model)
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;
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;*******************************************************************************
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.xlist
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include ulhelp.inc
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.list
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sBegin code
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assumes cs,code
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assumes ds,data
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page
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;***
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;lmul - 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 (DWORD)
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; 2nd pushed: multiplicand (DWORD)
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;
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;Exit:
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; DX:AX - 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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; CX
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;
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;Exceptions:
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;
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;*******************************************************************************
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if sizeC
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cProc _aFulmul,<PUBLIC>,<>
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cBegin nogen
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cEnd nogen
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else
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cProc _aNulmul,<PUBLIC>,<>
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cBegin nogen
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cEnd nogen
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endif
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if sizeC
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cProc _aFlmul,<PUBLIC>,<>
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else
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cProc _aNlmul,<PUBLIC>,<>
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endif
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cBegin
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A equ BPARGBAS[bp] ; stack address of a
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B equ BPARGBAS+4[bp] ; stack address of b
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;
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; AHI, BHI : upper 16 bits of A and B
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; ALO, BLO : lower 16 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 ax,HIWORD(A)
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mov cx,HIWORD(B)
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or cx,ax ;test for both hiwords zero.
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mov cx,LOWORD(B)
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jnz hard ;both are zero, just mult ALO and BLO
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mov ax,LOWORD(A)
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mul cx
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pop bp
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ret
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return 8 ; callee restores the stack
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hard:
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push bx
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mul cx ;ax has AHI, cx has BLO, so AHI * BLO
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mov bx,ax ;save result
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mov ax,LOWORD(A)
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mul word ptr HIWORD(B) ;ALO * BHI
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add bx,ax ;bx = ((ALO * BHI) + (AHI * BLO))
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mov ax,LOWORD(A) ;cx = BLO
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mul cx ;so dx:ax = ALO*BLO
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add dx,bx ;now dx has all the LO*HI stuff
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pop bx
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cEnd nolocals
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return 8 ; callee restores the stack
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sEnd
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end
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