94 lines
3.8 KiB
NASM
94 lines
3.8 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 msfs386
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xdefp "C",_fmsbintoieee
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defpe _fmsbintoieee
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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 MBF source float
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; edx - ptr to IEEE dest float
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mov eax,[eax] ; load MBF float
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; MBF exponent = 0 ?
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test eax,0ff000000h
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jne MBFNonZero ; yes, jump
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xor eax,eax ; IEEE 0.0
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mov [edx],eax ; store IEEE float
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ret ; return 0 (no overflow)
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; At this point:
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; eax - MBF source float
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; edx - ptr to IEEE dest float
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MBFNonZero: rol eax,9 ; rotate exponent for better analysis
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shr eax,1 ; shift out
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rcr al,1 ; move sign bit
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adc eax,eax ; shift back
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sub al,2 ; convert exponent
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jc MBFExp1 ; jump if MBF exponent 1
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je MBFExp2 ; jump if MBF exponent 2
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ror eax,9 ; rotate so IEEE float
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IEEEStore:
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mov [edx],eax ; store IEEE float
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xor eax,eax ; return 0 (no overflow)
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ret ; :
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MBFExp1: and al,1 ; zero exponent except implied 1
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ror eax,9 ; rotate so IEEE float
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sar eax,2 ; convert to IEEE denormal
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adc eax,0 ; add in round bit
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and eax,80FFFFFFh ; zero surplus sign bits
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jmp short IEEEStore ; continue
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MBFExp2: or al,1 ; set implied 1
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ror eax,9 ; rotate so IEEE float
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sar eax,1 ; convert to IEEE denormal
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adc eax,0 ; add in round bit
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and eax,80FFFFFFh ; zero surplus sign bit
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jmp short IEEEStore ; continue
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endproc _fmsbintoieee
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endmod
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end
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