kolibrios/programs/develop/open watcom/trunk/clib/cgsupp/fdfs386.asm

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;*****************************************************************************
;*
;* Open Watcom Project
;*
;* Portions Copyright (c) 1983-2002 Sybase, Inc. All Rights Reserved.
;*
;* ========================================================================
;*
;* This file contains Original Code and/or Modifications of Original
;* Code as defined in and that are subject to the Sybase Open Watcom
;* Public License version 1.0 (the 'License'). You may not use this file
;* except in compliance with the License. BY USING THIS FILE YOU AGREE TO
;* ALL TERMS AND CONDITIONS OF THE LICENSE. A copy of the License is
;* provided with the Original Code and Modifications, and is also
;* available at www.sybase.com/developer/opensource.
;*
;* The Original Code and all software distributed under the License are
;* distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
;* EXPRESS OR IMPLIED, AND SYBASE AND ALL CONTRIBUTORS HEREBY DISCLAIM
;* ALL SUCH WARRANTIES, INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF
;* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR
;* NON-INFRINGEMENT. Please see the License for the specific language
;* governing rights and limitations under the License.
;*
;* ========================================================================
;*
;* Description: WHEN YOU FIGURE OUT WHAT THIS FILE DOES, PLEASE
;* DESCRIBE IT HERE!
;*
;*****************************************************************************
;=========================================================================
;== Name: FDFS ==
;== Operation: Float double to float single conversion ==
;== Inputs: EDX:EAX double precision float ==
;== Outputs: EAX single precision float ==
;== Volatile: EDX destroyed ==
;=========================================================================
include mdef.inc
include struct.inc
modstart fdfs386
xdefp __FDFS
defpe __FDFS
push EBX ; save EBX
test EDX,07ff00000h ; check exponent
je short retzero ; if exponent = 0 then just return 0
sub EBX,EBX ; set to 0
_shl EAX,1 ; shift number over
_rcl EDX,1 ; ...
rcr EBX,1 ; save sign
add EAX,20000000h ; round floating point number
adc EDX,0 ; ...
je oflow ; overflow if exponent went to 0
cmp EDX,(03ffh+80h) shl 21 ; check for maximum exponent
jae oflow ; overflow if above or equal
cmp EDX,(03ffh-7eh) shl 21 ; check for minimum exponent
jb uflow ; underflow if below
sub EDX,(03ffh-7fh) shl 21 ; correct bias
_shl EAX,1 ; do rest of shift
_rcl EDX,1 ; ...
_shl EAX,1 ; ...
_rcl EDX,1 ; ...
or EDX,EBX ; put in sign bit
mov EAX,EDX ; get result into EAX
pop EBX ; restore EBX
ret ; return
oflow: mov EAX,7F800000h ; return maximum possible number
or EAX,EBX ; put in sign bit
pop EBX ; restore EBX
ret ; and return
uflow:
retzero:sub EAX,EAX ; set result to 0
pop EBX ; restore EBX
ret
endproc __FDFS
endmod
end