source: rtems/c/src/lib/libcpu/m68k/m68040/fpsp/sgetem.s @ 6f9c75c3

//
//      $Id$
//
//      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
//
//      THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE OF MOTOROLA 
//      The copyright notice above does not evidence any  
//      actual or intended publication of such source code.

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

        |section 8

#include "fpsp.defs"

        |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