106 lines
4.0 KiB
NASM
106 lines
4.0 KiB
NASM
;*****************************************************************************
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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 mdfd386
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xdefp "C",_dmsbintoieee
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defpe _dmsbintoieee
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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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else
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push ecx
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endif
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; At this point:
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; eax - ptr to MBF source double
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; edx - ptr to IEEE dest double
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; ecx - spare register
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; Check for and process MBF 0.0 first
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mov ecx,+4h[eax] ; load MBF double (hi)
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test ecx,0ff000000h ; MBF exponent = 0 ?
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jne MBFNonZero ; no, jump
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; MBF 0.0, store IEEE 0.0
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xor eax,eax ; make 0
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mov [edx],eax ; store IEEE 0.0 (lo)
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mov +4h[edx],eax ; store IEEE 0.0 (hi)
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ifndef __STACK__
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pop ecx ; clean up
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endif
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ret ; return 0 (no overflow)
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MBFNonZero: mov eax,[eax] ; load MBF double (lo)
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; At this point:
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; ecx:eax - MBF source double
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; edx - ptr to IEEE dest double
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rol ecx,9 ; rotate exponent & sign bit low
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shr ecx,1 ; move sign bit before exponent
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rcr cl,1 ; :
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adc ecx,ecx ; :
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ror ecx,9 ; rotate exponent & sign bit back
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; shift mantissa into place
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shrd eax,ecx,2 ; shift mantissa
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sar ecx,3 ; shift exponent & mantissa, save sign bit
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rcr eax,1 ; shift mantissa
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jc MBFRound ; jump if rounding up
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and ecx,8FFFFFFFh ; mask out surplus sign bits
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add ecx,37e00000h ; convert MBF to IEEE exponent
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IEEEStore:
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mov [edx],eax ; store IEEE double (lo)
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mov +4h[edx],ecx ; store IEEE double (hi)
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xor eax,eax ; 0
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ifndef __STACK__
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pop ecx ; clean up
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endif
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ret ; return 0 (no overflow)
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; add rounding bit
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MBFRound: and ecx,8FFFFFFFh ; mask out surplus sign bits
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add eax,1 ; add round bit
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adc ecx,37e00000h ; convert MBF to IEEE exponent
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jmp IEEEStore ; store result
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endproc _dmsbintoieee
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endmod
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end
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