310 lines
9.2 KiB
NASM
310 lines
9.2 KiB
NASM
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subttl emxtract - FXTRACT and FSCALE instructions
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page
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;*******************************************************************************
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;emxtract - FXTRACT and FSCALE instructions
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;
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; Microsoft Confidential
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;
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; Copyright (c) Microsoft Corporation 1991
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; All Rights Reserved
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;
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;Inputs:
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; edi = [CURstk]
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;
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;Revision History:
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;
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; [] 09/05/91 TP Initial 32-bit version.
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;
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;*******************************************************************************
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XtractStackOver:
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mov EMSEG:[SWcc],C1 ;Flag stack overflow
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XtractEmpty:
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;Result is two Indefinites (if exception masked)
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call StackError ;Put first indefinite at [edi] = ST(0)
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jz XtractExit ;Error was unmasked--just exit
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mov EMSEG:[CURstk],edi
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mov eax,EMSEG:[edi].ExpSgn
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mov EMSEG:[esi].ExpSgn,eax
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mov eax,EMSEG:[edi].lManHi
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mov EMSEG:[esi].lManHi,eax
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mov eax,EMSEG:[edi].lManLo
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mov EMSEG:[esi].lManLo,eax
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ret
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PrevStackWrap edi,Xtract
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EM_ENTRY eFXTRACT
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eFXTRACT:
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;edi = [CURstk]
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mov esi,edi ;Save current ST
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PrevStackElem edi,Xtract
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;edi = ST(0)
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;esi = ST(1) (operand)
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mov eax,EMSEG:[esi].ExpSgn
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;Exception priority requires reporting stack underflow (i.e., using an EMPTY)
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;before stack overflow (i.e., no place for result). Yes, both can happen
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;together if they've messed with the stack! (ST empty when ST(-1) isn't).
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cmp al,bTAG_EMPTY ;Is operand empty?
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jz XtractEmpty
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cmp EMSEG:[edi].bTag,bTAG_EMPTY ;Is there an empty spot?
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jnz XtractStackOver
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cmp al,bTAG_ZERO ;Is it special?
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jae XtractSpclOrZero
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XtractNormal:
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mov EMSEG:[CURstk],edi
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.erre TexpBias eq 0
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movzx ebx,ax ;Zero exponent
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;Save mantissa in ST(0)
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mov EMSEG:[edi].ExpSgn,ebx
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mov ebx,EMSEG:[esi].lManHi
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mov EMSEG:[edi].lManHi,ebx
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mov ebx,EMSEG:[esi].lManLo
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mov EMSEG:[edi].lManLo,ebx
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mov edi,esi ;Save ST(1) pointer in edi
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shr eax,16 ;Move exponent down
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call NormInt16 ;in emload.asm
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;mantissa in ebx:esi, exponent in high ecx, sign in ch bit 7, tag in cl
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mov EMSEG:[edi].lManLo,esi
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mov EMSEG:[edi].lManHi,ebx
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mov EMSEG:[edi].ExpSgn,ecx
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XtractExit:
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ret
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XtractSpcl:
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cmp al,bTAG_INF
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jz XtractInf
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cmp al,bTAG_NAN
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jz XtractNAN
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;Must be denormal. Change tag to VALID or SNGL.
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cmp EMSEG:[esi].lManLo,0 ;Any bits in low half?
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.erre bTAG_VALID eq 1
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.erre bTAG_SNGL eq 0
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setnz al ;if low half==0 then al=0 else al=1
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mov EMSEG:[CURerr],Denormal
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test EMSEG:[CWmask],Denormal ;Is it masked?
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jnz XtractNormal ;If so, ignore denormalization
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ret
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XtractSpclOrZero:
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ja XtractSpcl
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;Operand is zero. Result is ST(0) = 0 (same sign), ST(1) = -infinity
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mov EMSEG:[CURerr],ZeroDivide
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test EMSEG:[CWmask],ZeroDivide ;Exception masked?
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jz XtractExit
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mov EMSEG:[CURstk],edi
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mov EMSEG:[edi].ExpSgn,eax
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mov eax,EMSEG:[esi].lManHi
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mov EMSEG:[edi].lManHi,eax
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mov eax,EMSEG:[esi].lManLo
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mov EMSEG:[edi].lManLo,eax
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mov EMSEG:[esi].ExpSgn,(IexpMax-IexpBias+TexpBias) shl 16 + bSign shl 8 + bTAG_INF
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mov EMSEG:[esi].bMan7,80H ;Change zero to infinity
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ret
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XtractInf:
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;Result is ST(0) = infinity (same sign), ST(1) = +infinity
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mov EMSEG:[esi].bSgn,0 ;Ensure ST(1) is positive
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XtractQNAN:
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mov EMSEG:[CURstk],edi
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mov EMSEG:[edi].ExpSgn,eax
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mov eax,EMSEG:[esi].lManHi
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mov EMSEG:[edi].lManHi,eax
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mov eax,EMSEG:[esi].lManLo
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mov EMSEG:[edi].lManLo,eax
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ret
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XtractNAN:
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;Result is two QNANs, signal Invalid Operation if SNAN
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test EMSEG:[esi].bMan7,40H ;Is it SNAN?
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jnz XtractQNAN
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mov EMSEG:[CURerr],Invalid
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test EMSEG:[CWmask],Invalid
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jz XtractExit
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or EMSEG:[esi].bMan7,40H ;Change to QNAN
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jmp XtractQNAN
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;*******************************************************************************
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;
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;FSCALE instruction
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;Actual instruction entry point is in emarith.asm
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;Dispatch table for scale
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;
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;One operand has been loaded into ecx:ebx:esi ("source"), the other is
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;pointed to by edi ("dest").
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;
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;Tag of source is shifted. Tag values are as follows:
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.erre TAG_SNGL eq 0 ;SINGLE: low 32 bits are zero
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.erre TAG_VALID eq 1
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.erre TAG_ZERO eq 2
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.erre TAG_SPCL eq 3 ;NAN, Infinity, Denormal, Empty
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;Any special case routines not found in this file are in emarith.asm
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tFscaleDisp label dword ;Source (reg) Dest (*[di] = ST)
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dd ScaleDouble ;single single
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dd ScaleDouble ;single double
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dd ScaleX ;single zero
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dd ScaleSpclDest ;single special
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dd ScaleDouble ;double single
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dd ScaleDouble ;double double
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dd ScaleX ;double zero
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dd ScaleSpclDest ;double special
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dd ScaleX ;zero single
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dd ScaleX ;zero double
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dd ScaleX ;zero zero
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dd ScaleSpclDest ;zero special
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dd ScaleSpclSource ;special single
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dd ScaleSpclSource ;special double
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dd ScaleSpclSource ;special zero
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dd TwoOpBothSpcl ;special special
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dd ScaleTwoInf ;Two infinites
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;The unmasked response to overflow and underflow with FSCALE is complicated
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;by the extreme range it can generate. Normally, the exponent is biased
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;by 24,576 in the appropriate direction to bring it back into range.
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;This may not be enough, however. If it isn't, a result of infinity
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;(with the correct sign) is returned for overflow, regardless of the
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;rounding mode. For underflow, zero (with the correct sign) is returned,
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;even if it could be represented as a denormal. This may be the only
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;operation in which the unmasked response destroys the operands beyond
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;recovery.
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BigScale:
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;Scale factor is much too big. Just shift mantissa right two bits to get
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;MSB out of sign bit and ensure no overflow when we add.
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mov cl,2 ;Always shift 2 bits if it's big
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jmp ScaleCont
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ScaleDouble:
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;ebx:esi = ST(1) mantissa
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;ecx = ST(1) sign in bit 15, exponent in high half
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;edi = pointer to ST(0)
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rol ecx,16 ;Bring exponent down, sign to top
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or ch,ch ;Check sign of exponent
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js ScaleX ;No work if less than zero
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cmp cx,30 ;Scale factor exceed 30 bits?
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jge BigScale
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not cl ;cl = amount to shift right (mod 32)
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ScaleCont:
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shr ebx,cl ;ebx = exponent adjustment for ST(0)
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;Use two's complement if negative (complement and increment)
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mov eax,ecx
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cdq ;Extend sign through edx
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xor ebx,edx ;Complement if negative
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sub ebx,edx ;Increment if negative
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;Scale exponent
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movsx eax,EMSEG:[edi].wExp ;Get exponent to adjust
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add eax,ebx ;Can't overflow
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cmp eax,IexpMax-IexpBias ;Within normal range?
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jge ScaleOverflow
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cmp eax,IexpMin-IexpBias
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jle ScaleUnderflow
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SaveScaledExp:
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;Result fit withing normal range
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mov EMSEG:[edi].wExp,ax ;Update exponent of ST(0)
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ScaleX:
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ret
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ScaleOverflow:
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;eax = exponent that's too big
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mov EMSEG:[CURerr],Overflow
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test EMSEG:[CWmask],Overflow ;Is exception unmasked?
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jz UnmaskedScaleOvfl
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;Produce masked overflow response
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mov al,EMSEG:[CWcntl] ;Get rounding control
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mov ah,al
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;Return max value if RCup bit = 1 and -, or RCdown bit = 1 and +
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;i.e., RCup & sign OR RCdown & not sign
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.erre RCchop eq RCup + RCdown ;Always return max value
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.erre RCnear eq 0 ;Never return max value
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sar ch,7 ;Expand sign through whole byte
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.erre (RCdown and bSign) eq 0 ;Don't want to change real sign
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xor ch,RCdown ;Flip sign for RCdown bit
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and ah,ch ;RCup & sign OR RCdown & not sign
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jz ScaleToInfinity ;Save Infinity
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;Get max value
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sub ecx,1 shl 16 ;Drop exponent by 1
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xor esi,esi
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dec esi ;esi == -1
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mov ebx,esi
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SaveScaleMax:
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mov EMSEG:[edi].lManLo,esi
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mov EMSEG:[edi].lManHi,ebx
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mov EMSEG:[edi].ExpSgn,ecx
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ret
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UnmaskedScaleOvfl:
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sub eax,UnderBias ;Unmasked response
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cmp eax,IexpMax-IexpBias ;Within normal range now?
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jl SaveScaledExp ;Use exponent biased by 24K
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ScaleToInfinity:
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mov ebx,1 shl 31
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xor esi,esi
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mov ecx,(IexpMax-IexpBias+TexpBias) shl 16 + bTAG_INF
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mov ch,EMSEG:[edi].bSgn ;Give it same sign
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jmp SaveScaleMax ;Use infinity
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ScaleUnderflow:
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;eax = exponent that's too big
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test EMSEG:[CWmask],Underflow ;Is exception unmasked?
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jz ScaleSetUnder
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cmp eax,-32768 ;Does exponent fit in 16 bits?
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jg @F
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mov ax,-32768 ;Max value
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@@:
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;Set up for denormalizer
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mov ebx,EMSEG:[edi].lManHi
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mov esi,EMSEG:[edi].lManLo
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shrd ecx,eax,16 ;Move exponent to high end of ecx
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mov ch,EMSEG:[edi].bSgn ;Keep sign
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xor eax,eax ;No sticky bits
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mov EMSEG:[Result],edi
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jmp Denormalize ;In emround.asm
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ScaleSetUnder:
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;Underflow exception not masked. Adjust exponent and try again.
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mov EMSEG:[CURerr],Underflow
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add eax,UnderBias ;Unmasked response
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cmp eax,IexpMin-IexpBias ;Within normal range now?
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jg SaveScaledExp ;Use exponent biased by 24K
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mov EMSEG:[CURerr],Underflow
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ScaleToZero:
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mov ecx,bTAG_ZERO
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mov ch,EMSEG:[edi].bSgn ;Give it same sign
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xor ebx,ebx
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mov esi,ebx
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jmp SaveScaleMax ;Set to zero
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;***
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ScaleSpclDest:
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mov al,EMSEG:[edi].bTag ;Pick up tag
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cmp al,bTAG_INF ;Scaling infinity?
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jz ScaleRet ;No change if so
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jmp SpclDest ;In emarith.asm
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ScaleRet:
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ret
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;***
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ScaleSpclSource:
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cmp cl,bTAG_INF ;Scaling by infinity?
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jnz SpclSource ;in emarith.asm
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or ch,ch ;Scaling by -infinity?
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js ScaleToZero
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cmp EMSEG:[edi].bTag,bTAG_ZERO ;Zero scaled by +infinity?
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jnz ScaleToInfinity
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jmp ReturnIndefinite ;Invalid operation
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;***
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ScaleTwoInf:
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or ch,ch ;Scaling by +infinity?
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jns ScaleRet ;All done then
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;Scaling infinity by -infinity
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jmp ReturnIndefinite ;Invalid operation
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