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195 lines
4.1 KiB
195 lines
4.1 KiB
page ,132
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subttl emfmul.asm - Multiplication
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;***
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;emfmisc.asm - Multiplication
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;
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; Copyright (c) 1986-89, Microsoft Corporation
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;
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;Purpose:
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; Multiplication
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;
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;
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; This Module contains Proprietary Information of Microsoft
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; Corporation and should be treated as Confidential.
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;
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;Revision History:
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; See emulator.hst
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;
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;*******************************************************************************
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;-----------------------------------------;
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; ;
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; Multiplication ;
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; ;
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;-----------------------------------------;
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; Perform multiply by summing partial products of 16x16 hardware multiply.
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; Before each multiply, the operands are checked for zero to see if it can be
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; skipped, since it's a slow operation on the 8086. The sum is kept in
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; registers as much as possible. Any insignificant bits lost are ORed together
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; and kept in a word on the top of the stack. This can be used for sticky bit
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; rounding. First we will need some macros.
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ProfBegin FMUL
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MULP MACRO SIOFFSET,DIOFFSET,NEXTLOC
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;Will multiply the words found at the given offsets if those words
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;are non-0. since we assume the numbers are normalized and the
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;most significant word has offset 6 we know that words with offset
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;6 are non-0 hence the conditional code in this macro.
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MOV AX,SIOFFSET[esi]
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IF SIOFFSET - 6 ;When SI offset is 6 it is most sig word hence not 0
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OR AX,AX
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JZ short NEXTLOC
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ENDIF
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IF DIOFFSET - 6
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MOV DX,DIOFFSET[edi]
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OR DX,DX
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JZ short NEXTLOC
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MUL DX
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ELSE
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MUL WORD PTR DIOFFSET[edi]
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ENDIF
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ENDM
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ADDP MACRO HI,MID,LO
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;Will add the double word result of a multiply to the triple word
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; at HI:MID:LO using HI to record overflow
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ADD LO,AX
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ADC MID,DX
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ADC HI,0
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ENDM
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STICKY MACRO R
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;R is the register containing the least significant word which
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;should be ORed to the sticky bit (kept on the stack) and then
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;cleared so the register can be reused
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POP eax
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OR AX,R
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PUSH eax
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XOR R,R
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ENDM
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page
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RMBRQQ: ; Routine MUL Both must see if we have two singles.
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if fastSP
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MOV BX,DX
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XOR BX,Single + 256*Single
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TEST BX,Single + 256*Single
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JNZ RMDRQQ
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MOV BX,OFFSET TMSRQQ
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JMP [BX]
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endif ;fastSP
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pub RMDRQQ ;RoutineMulDouble SI & DI point to valid non-0 reals
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; AX CX are the exponents
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; DL DH are the signs
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if fastSP
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CALL CoerceToDouble ; insure that both args are double
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endif ;fastSP
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PUSH ebp ; Must save BP
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MOV BH,DH ; Save Single double flag
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XOR DH,DL ; Get sign onto stack
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PUSH edx
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ADD AX,CX ; New exponent is sum of old plus 1
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INC AX ; because of the normalize step
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PUSH eax ; Save it while we Multiply
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AND BH,DL
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pub PROD1
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XOR BX,BX
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MOV BP,BX
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MOV CX,BX
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MULP 0,0,PROD2
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MOV BP,AX ; Save insignificant bits
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MOV CX,DX
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pub PROD2
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PUSH ebp ; Save Sticky bit on stack
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xor ebp, ebp ; bp is now the working high word of bp:bx:cx
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MULP 0,2,PROD3
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ADDP BP,BX,CX
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pub PROD3
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MULP 2,0,PROD4
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ADDP BP,BX,CX
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pub PROD4
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STICKY CX
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MULP 0,4,PROD5
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ADDP CX,BP,BX
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pub PROD5
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MULP 2,2,PROD6
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ADDP CX,BP,BX
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pub PROD6
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MULP 4,0,PROD7
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ADDP CX,BP,BX
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pub PROD7
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STICKY BX
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MULP 0,6,PROD8
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ADDP BX,CX,BP
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pub PROD8
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MULP 2,4,PROD9
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ADDP BX,CX,BP
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pub PROD9
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MULP 4,2,PROD10
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ADDP BX,CX,BP
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pub PROD10
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MULP 6,0,PROD11
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ADDP BX,CX,BP
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pub PROD11
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MOV DX,BP ; Everything but guard and round go to sticky
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AND BP,03FFFH
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STICKY BP
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PUSH edx ; Save guard and round on stack
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MULP 2,6,PROD12
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ADDP BP,BX,CX
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pub PROD12
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MULP 4,4,PROD13
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ADDP BP,BX,CX
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pub PROD13
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MULP 6,2,PROD14
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ADDP BP,BX,CX
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pub PROD14
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PUSH ecx ; Save LSW on stack (not enough registers)
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XOR CX,CX
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MULP 4,6,PROD15
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ADDP CX,BP,BX
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pub PROD15
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MULP 6,4,PROD16
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ADDP CX,BP,BX
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pub PROD16
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MULP 6,6,PROD17
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ADD AX,BP
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ADC DX,CX
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POP ecx
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POP ebp ; Result in DX:AX:BX:CX:BP Sticky on stack
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MOV DI,DX
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MOV DX,CX
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MOV CX,BX
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MOV BX,AX ; Result in DI:BX:CX:DX:BP
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POP eax ; Merge Sticky bit into BP
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OR AX,AX
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JZ short STBITOK
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OR BP,1
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pub STBITOK
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POP esi ; Exponent in SI, Sign on Stack, Old BP on Stack
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JMP NORMSHF ; Result must be normalized at most 1 bit
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ProfEnd FMUL
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