110 lines
4.5 KiB
NASM
110 lines
4.5 KiB
NASM
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;*****************************************************************************
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;*
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;* Open Watcom Project
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;*
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;* Portions Copyright (c) 1983-2002 Sybase, Inc. All Rights Reserved.
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;*
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;* ========================================================================
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;*
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;* This file contains Original Code and/or Modifications of Original
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;* Code as defined in and that are subject to the Sybase Open Watcom
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;* Public License version 1.0 (the 'License'). You may not use this file
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;* except in compliance with the License. BY USING THIS FILE YOU AGREE TO
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;* ALL TERMS AND CONDITIONS OF THE LICENSE. A copy of the License is
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;* provided with the Original Code and Modifications, and is also
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;* available at www.sybase.com/developer/opensource.
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;*
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;* The Original Code and all software distributed under the License are
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;* distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
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;* EXPRESS OR IMPLIED, AND SYBASE AND ALL CONTRIBUTORS HEREBY DISCLAIM
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;* ALL SUCH WARRANTIES, INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF
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;* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR
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;* NON-INFRINGEMENT. Please see the License for the specific language
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;* governing rights and limitations under the License.
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;*
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;* ========================================================================
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;*
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;* Description: WHEN YOU FIGURE OUT WHAT THIS FILE DOES, PLEASE
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;* DESCRIBE IT HERE!
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;*
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;*****************************************************************************
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include mdef.inc
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include struct.inc
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modstart fsms386
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xdefp "C",_fieeetomsbin
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defpe _fieeetomsbin
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ifdef __STACK__
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mov eax,dword ptr +4H[esp]
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mov edx,dword ptr +8H[esp]
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endif
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; At this point:
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; eax - ptr to IEEE source float
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; edx - ptr to MBF dest float
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mov eax,[eax] ; load IEEE float
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test eax,7fe00000h ; IEEE exponent != 0 or convertable
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; denormal ?
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jne IEEENonZero ; :
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; IEEE Zero or IEEE unconvertable denormal, store MBF Zero
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xor eax,eax ; 0
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mov [edx],eax ; store MBF 0.0F
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ret ; return 0 (no overflow)
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; At this point:
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; eax - IEEE source float
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; edx - ptr to MBF dest float
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IEEENonZero: rol eax,9 ; rotate for exponent analysis
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test al,al ; IEEE convertable denormal ?
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je IEEEDenormal ; yes, jump
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add al,2 ; MBF exponent = IEEE exponent + 2
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jc IEEEOverflow ; jump if overflow
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shr eax,1 ; rotate sign bit and exponent
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adc al,al ; :
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adc eax,eax ; :
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ror eax,9 ; rotate so MBF float
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MBFStore: mov [edx],eax ; store MBF float
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xor eax,eax ; 0
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ret ; return 0 (no overflow)
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; One of leading 2 bits of mantissa is a 1
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IEEEDenormal:
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ifndef __STACK__
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push ecx ; save register
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endif
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mov ecx,eax ; save sign bit and exponent
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and ah,0FEh ; eliminate sign bit
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DenormalLoop: inc ecx ; increment count
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add eax,eax ; shift mantissa
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jnc DenormalLoop ; loop while no implied 1
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xor ecx,3h ; invert count (new exponent)
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shr ecx,1 ; rotate exponent and sign bit
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adc cl,cl ; :
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adc ecx,ecx ; :
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shrd eax,ecx,9 ; combine mantissa (eax) and
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; exponent& sign bit (ecx)
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ifndef __STACK__
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pop ecx ; restore register
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endif
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jmp MBFStore ; continue
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IEEEOverflow: rol eax,15 ; rotate sign bit into place
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or eax,0FF7FFFFFh ; set MBF exponent and mantissa to
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; maximum but preserve MBF sign
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mov [edx],eax ; store MBF float
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and eax,1 ; 1
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ret ; return 1 (overflow)
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endproc _fieeetomsbin
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endmod
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end
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