fdfs386.asm

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;*****************************************************************************
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;*                            Open Watcom Project
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;=========================================================================
;==     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