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|
|       sgetem.sa 3.1 12/10/90
|
|       The entry point sGETEXP returns the exponent portion
|       of the input argument.  The exponent bias is removed
|       and the exponent value is returned as an extended
|       precision number in fp0.  sGETEXPD handles denormalized
|       numbers.
|
|       The entry point sGETMAN extracts the mantissa of the
|       input argument.  The mantissa is converted to an
|       extended precision number and returned in fp0.  The
|       range of the result is [1.0 - 2.0).
|
|
|       Input:  Double-extended number X in the ETEMP space in
|               the floating-point save stack.
|
|       Output: The functions return exp(X) or man(X) in fp0.
|
|       Modified: fp0.
|
|
|               Copyright (C) Motorola, Inc. 1990
|                       All Rights Reserved
|
|       For details on the license for this file, please see the
|       file, README, in this same directory.

|SGETEM idnt    2,1 | Motorola 040 Floating Point Software Package

        |section 8

#include "fpsp.h"

        |xref   nrm_set

|
| This entry point is used by the unimplemented instruction exception
| handler.  It points a0 to the input operand.
|
|
|
|       SGETEXP
|

        .global sgetexp
sgetexp:
        movew   LOCAL_EX(%a0),%d0       |get the exponent
        bclrl   #15,%d0         |clear the sign bit
        subw    #0x3fff,%d0     |subtract off the bias
        fmovew  %d0,%fp0                |move the exp to fp0
        rts

        .global sgetexpd
sgetexpd:
        bclrb   #sign_bit,LOCAL_EX(%a0)
        bsr     nrm_set         |normalize (exp will go negative)
        movew   LOCAL_EX(%a0),%d0       |load resulting exponent into d0
        subw    #0x3fff,%d0     |subtract off the bias
        fmovew  %d0,%fp0                |move the exp to fp0
        rts
|
|
| This entry point is used by the unimplemented instruction exception
| handler.  It points a0 to the input operand.
|
|
|
|       SGETMAN
|
|
| For normalized numbers, leave the mantissa alone, simply load
| with an exponent of +/- $3fff.
|
        .global sgetman
sgetman:
        movel   USER_FPCR(%a6),%d0
        andil   #0xffffff00,%d0 |clear rounding precision and mode
        fmovel  %d0,%fpcr               |this fpcr setting is used by the 882
        movew   LOCAL_EX(%a0),%d0       |get the exp (really just want sign bit)
        orw     #0x7fff,%d0     |clear old exp
        bclrl   #14,%d0         |make it the new exp +-3fff
        movew   %d0,LOCAL_EX(%a0)       |move the sign & exp back to fsave stack
        fmovex  (%a0),%fp0      |put new value back in fp0
        rts

|
| For denormalized numbers, shift the mantissa until the j-bit = 1,
| then load the exponent with +/1 $3fff.
|
        .global sgetmand
sgetmand:
        movel   LOCAL_HI(%a0),%d0       |load ms mant in d0
        movel   LOCAL_LO(%a0),%d1       |load ls mant in d1
        bsr     shft            |shift mantissa bits till msbit is set
        movel   %d0,LOCAL_HI(%a0)       |put ms mant back on stack
        movel   %d1,LOCAL_LO(%a0)       |put ls mant back on stack
        bras    sgetman

|
|       SHFT
|
|       Shifts the mantissa bits until msbit is set.
|       input:
|               ms mantissa part in d0
|               ls mantissa part in d1
|       output:
|               shifted bits in d0 and d1
shft:
        tstl    %d0             |if any bits set in ms mant
        bnes    upper           |then branch
|                               ;else no bits set in ms mant
        tstl    %d1             |test if any bits set in ls mant
        bnes    cont            |if set then continue
        bras    shft_end        |else return
cont:
        movel   %d3,-(%a7)      |save d3
        exg     %d0,%d1         |shift ls mant to ms mant
        bfffo   %d0{#0:#32},%d3 |find first 1 in ls mant to d0
        lsll    %d3,%d0         |shift first 1 to integer bit in ms mant
        movel   (%a7)+,%d3      |restore d3
        bras    shft_end
upper:

        moveml  %d3/%d5/%d6,-(%a7)      |save registers
        bfffo   %d0{#0:#32},%d3 |find first 1 in ls mant to d0
        lsll    %d3,%d0         |shift ms mant until j-bit is set
        movel   %d1,%d6         |save ls mant in d6
        lsll    %d3,%d1         |shift ls mant by count
        movel   #32,%d5
        subl    %d3,%d5         |sub 32 from shift for ls mant
        lsrl    %d5,%d6         |shift off all bits but those that will
|                               ;be shifted into ms mant
        orl     %d6,%d0         |shift the ls mant bits into the ms mant
        moveml  (%a7)+,%d3/%d5/%d6      |restore registers
shft_end:
        rts

        |end