arch/m68k/fpsp040/sgetem.S

   1 |
   2 |       sgetem.sa 3.1 12/10/90
   3 |
   4 |       The entry point sGETEXP returns the exponent portion
   5 |       of the input argument.  The exponent bias is removed
   6 |       and the exponent value is returned as an extended
   7 |       precision number in fp0.  sGETEXPD handles denormalized
   8 |       numbers.
   9 |
  10 |       The entry point sGETMAN extracts the mantissa of the
  11 |       input argument.  The mantissa is converted to an
  12 |       extended precision number and returned in fp0.  The
  13 |       range of the result is [1.0 - 2.0).
  14 |
  15 |
  16 |       Input:  Double-extended number X in the ETEMP space in
  17 |               the floating-point save stack.
  18 |
  19 |       Output: The functions return exp(X) or man(X) in fp0.
  20 |
  21 |       Modified: fp0.
  22 |
  23 |
  24 |               Copyright (C) Motorola, Inc. 1990
  25 |                       All Rights Reserved
  26 |
  27 |       THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE OF MOTOROLA
  28 |       The copyright notice above does not evidence any
  29 |       actual or intended publication of such source code.
  30
  31 |SGETEM idnt    2,1 | Motorola 040 Floating Point Software Package
  32
  33         |section 8
  34
  35 #include "fpsp.h"
  36
  37         |xref   nrm_set
  38
  39 |
  40 | This entry point is used by the unimplemented instruction exception
  41 | handler.  It points a0 to the input operand.
  42 |
  43 |
  44 |
  45 |       SGETEXP
  46 |
  47
  48         .global sgetexp
  49 sgetexp:
  50         movew   LOCAL_EX(%a0),%d0       |get the exponent
  51         bclrl   #15,%d0         |clear the sign bit
  52         subw    #0x3fff,%d0     |subtract off the bias
  53         fmovew  %d0,%fp0                |move the exp to fp0
  54         rts
  55
  56         .global sgetexpd
  57 sgetexpd:
  58         bclrb   #sign_bit,LOCAL_EX(%a0)
  59         bsr     nrm_set         |normalize (exp will go negative)
  60         movew   LOCAL_EX(%a0),%d0       |load resulting exponent into d0
  61         subw    #0x3fff,%d0     |subtract off the bias
  62         fmovew  %d0,%fp0                |move the exp to fp0
  63         rts
  64 |
  65 |
  66 | This entry point is used by the unimplemented instruction exception
  67 | handler.  It points a0 to the input operand.
  68 |
  69 |
  70 |
  71 |       SGETMAN
  72 |
  73 |
  74 | For normalized numbers, leave the mantissa alone, simply load
  75 | with an exponent of +/- $3fff.
  76 |
  77         .global sgetman
  78 sgetman:
  79         movel   USER_FPCR(%a6),%d0
  80         andil   #0xffffff00,%d0 |clear rounding precision and mode
  81         fmovel  %d0,%fpcr               |this fpcr setting is used by the 882
  82         movew   LOCAL_EX(%a0),%d0       |get the exp (really just want sign bit)
  83         orw     #0x7fff,%d0     |clear old exp
  84         bclrl   #14,%d0         |make it the new exp +-3fff
  85         movew   %d0,LOCAL_EX(%a0)       |move the sign & exp back to fsave stack
  86         fmovex  (%a0),%fp0      |put new value back in fp0
  87         rts
  88
  89 |
  90 | For denormalized numbers, shift the mantissa until the j-bit = 1,
  91 | then load the exponent with +/1 $3fff.
  92 |
  93         .global sgetmand
  94 sgetmand:
  95         movel   LOCAL_HI(%a0),%d0       |load ms mant in d0
  96         movel   LOCAL_LO(%a0),%d1       |load ls mant in d1
  97         bsr     shft            |shift mantissa bits till msbit is set
  98         movel   %d0,LOCAL_HI(%a0)       |put ms mant back on stack
  99         movel   %d1,LOCAL_LO(%a0)       |put ls mant back on stack
 100         bras    sgetman
 101
 102 |
 103 |       SHFT
 104 |
 105 |       Shifts the mantissa bits until msbit is set.
 106 |       input:
 107 |               ms mantissa part in d0
 108 |               ls mantissa part in d1
 109 |       output:
 110 |               shifted bits in d0 and d1
 111 shft:
 112         tstl    %d0             |if any bits set in ms mant
 113         bnes    upper           |then branch
 114 |                               ;else no bits set in ms mant
 115         tstl    %d1             |test if any bits set in ls mant
 116         bnes    cont            |if set then continue
 117         bras    shft_end        |else return
 118 cont:
 119         movel   %d3,-(%a7)      |save d3
 120         exg     %d0,%d1         |shift ls mant to ms mant
 121         bfffo   %d0{#0:#32},%d3 |find first 1 in ls mant to d0
 122         lsll    %d3,%d0         |shift first 1 to integer bit in ms mant
 123         movel   (%a7)+,%d3      |restore d3
 124         bras    shft_end
 125 upper:
 126
 127         moveml  %d3/%d5/%d6,-(%a7)      |save registers
 128         bfffo   %d0{#0:#32},%d3 |find first 1 in ls mant to d0
 129         lsll    %d3,%d0         |shift ms mant until j-bit is set
 130         movel   %d1,%d6         |save ls mant in d6
 131         lsll    %d3,%d1         |shift ls mant by count
 132         movel   #32,%d5
 133         subl    %d3,%d5         |sub 32 from shift for ls mant
 134         lsrl    %d5,%d6         |shift off all bits but those that will
 135 |                               ;be shifted into ms mant
 136         orl     %d6,%d0         |shift the ls mant bits into the ms mant
 137         moveml  (%a7)+,%d3/%d5/%d6      |restore registers
 138 shft_end:
 139         rts
 140
 141         |end