85 lines
3.7 KiB
NASM
85 lines
3.7 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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;=========================================================================
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;== Name: FDFS ==
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;== Operation: Float double to float single conversion ==
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;== Inputs: EDX:EAX double precision float ==
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;== Outputs: EAX single precision float ==
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;== Volatile: EDX destroyed ==
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;=========================================================================
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include mdef.inc
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include struct.inc
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modstart fdfs386
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xdefp __FDFS
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defpe __FDFS
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push EBX ; save EBX
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test EDX,07ff00000h ; check exponent
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je short retzero ; if exponent = 0 then just return 0
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sub EBX,EBX ; set to 0
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_shl EAX,1 ; shift number over
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_rcl EDX,1 ; ...
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rcr EBX,1 ; save sign
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add EAX,20000000h ; round floating point number
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adc EDX,0 ; ...
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je oflow ; overflow if exponent went to 0
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cmp EDX,(03ffh+80h) shl 21 ; check for maximum exponent
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jae oflow ; overflow if above or equal
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cmp EDX,(03ffh-7eh) shl 21 ; check for minimum exponent
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jb uflow ; underflow if below
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sub EDX,(03ffh-7fh) shl 21 ; correct bias
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_shl EAX,1 ; do rest of shift
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_rcl EDX,1 ; ...
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_shl EAX,1 ; ...
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_rcl EDX,1 ; ...
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or EDX,EBX ; put in sign bit
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mov EAX,EDX ; get result into EAX
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pop EBX ; restore EBX
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ret ; return
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oflow: mov EAX,7F800000h ; return maximum possible number
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or EAX,EBX ; put in sign bit
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pop EBX ; restore EBX
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ret ; and return
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uflow:
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retzero:sub EAX,EAX ; set result to 0
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pop EBX ; restore EBX
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ret
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endproc __FDFS
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endmod
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end
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