arch/m68k/fpsp040/stanh.S

   1 |
   2 |       stanh.sa 3.1 12/10/90
   3 |
   4 |       The entry point sTanh computes the hyperbolic tangent of
   5 |       an input argument; sTanhd does the same except for denormalized
   6 |       input.
   7 |
   8 |       Input: Double-extended number X in location pointed to
   9 |               by address register a0.
  10 |
  11 |       Output: The value tanh(X) returned in floating-point register Fp0.
  12 |
  13 |       Accuracy and Monotonicity: The returned result is within 3 ulps in
  14 |               64 significant bit, i.e. within 0.5001 ulp to 53 bits if the
  15 |               result is subsequently rounded to double precision. The
  16 |               result is provably monotonic in double precision.
  17 |
  18 |       Speed: The program stanh takes approximately 270 cycles.
  19 |
  20 |       Algorithm:
  21 |
  22 |       TANH
  23 |       1. If |X| >= (5/2) log2 or |X| <= 2**(-40), go to 3.
  24 |
  25 |       2. (2**(-40) < |X| < (5/2) log2) Calculate tanh(X) by
  26 |               sgn := sign(X), y := 2|X|, z := expm1(Y), and
  27 |               tanh(X) = sgn*( z/(2+z) ).
  28 |               Exit.
  29 |
  30 |       3. (|X| <= 2**(-40) or |X| >= (5/2) log2). If |X| < 1,
  31 |               go to 7.
  32 |
  33 |       4. (|X| >= (5/2) log2) If |X| >= 50 log2, go to 6.
  34 |
  35 |       5. ((5/2) log2 <= |X| < 50 log2) Calculate tanh(X) by
  36 |               sgn := sign(X), y := 2|X|, z := exp(Y),
  37 |               tanh(X) = sgn - [ sgn*2/(1+z) ].
  38 |               Exit.
  39 |
  40 |       6. (|X| >= 50 log2) Tanh(X) = +-1 (round to nearest). Thus, we
  41 |               calculate Tanh(X) by
  42 |               sgn := sign(X), Tiny := 2**(-126),
  43 |               tanh(X) := sgn - sgn*Tiny.
  44 |               Exit.
  45 |
  46 |       7. (|X| < 2**(-40)). Tanh(X) = X.       Exit.
  47 |
  48
  49 |               Copyright (C) Motorola, Inc. 1990
  50 |                       All Rights Reserved
  51 |
  52 |       THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE OF MOTOROLA
  53 |       The copyright notice above does not evidence any
  54 |       actual or intended publication of such source code.
  55
  56 |STANH  idnt    2,1 | Motorola 040 Floating Point Software Package
  57
  58         |section        8
  59
  60 #include "fpsp.h"
  61
  62         .set    X,FP_SCR5
  63         .set    XDCARE,X+2
  64         .set    XFRAC,X+4
  65
  66         .set    SGN,L_SCR3
  67
  68         .set    V,FP_SCR6
  69
  70 BOUNDS1:        .long 0x3FD78000,0x3FFFDDCE | ... 2^(-40), (5/2)LOG2
  71
  72         |xref   t_frcinx
  73         |xref   t_extdnrm
  74         |xref   setox
  75         |xref   setoxm1
  76
  77         .global stanhd
  78 stanhd:
  79 |--TANH(X) = X FOR DENORMALIZED X
  80
  81         bra             t_extdnrm
  82
  83         .global stanh
  84 stanh:
  85         fmovex          (%a0),%fp0      | ...LOAD INPUT
  86
  87         fmovex          %fp0,X(%a6)
  88         movel           (%a0),%d0
  89         movew           4(%a0),%d0
  90         movel           %d0,X(%a6)
  91         andl            #0x7FFFFFFF,%d0
  92         cmp2l           BOUNDS1(%pc),%d0        | ...2**(-40) < |X| < (5/2)LOG2 ?
  93         bcss            TANHBORS
  94
  95 |--THIS IS THE USUAL CASE
  96 |--Y = 2|X|, Z = EXPM1(Y), TANH(X) = SIGN(X) * Z / (Z+2).
  97
  98         movel           X(%a6),%d0
  99         movel           %d0,SGN(%a6)
 100         andl            #0x7FFF0000,%d0
 101         addl            #0x00010000,%d0 | ...EXPONENT OF 2|X|
 102         movel           %d0,X(%a6)
 103         andl            #0x80000000,SGN(%a6)
 104         fmovex          X(%a6),%fp0             | ...FP0 IS Y = 2|X|
 105
 106         movel           %d1,-(%a7)
 107         clrl            %d1
 108         fmovemx %fp0-%fp0,(%a0)
 109         bsr             setoxm1         | ...FP0 IS Z = EXPM1(Y)
 110         movel           (%a7)+,%d1
 111
 112         fmovex          %fp0,%fp1
 113         fadds           #0x40000000,%fp1        | ...Z+2
 114         movel           SGN(%a6),%d0
 115         fmovex          %fp1,V(%a6)
 116         eorl            %d0,V(%a6)
 117
 118         fmovel          %d1,%FPCR               |restore users exceptions
 119         fdivx           V(%a6),%fp0
 120         bra             t_frcinx
 121
 122 TANHBORS:
 123         cmpl            #0x3FFF8000,%d0
 124         blt             TANHSM
 125
 126         cmpl            #0x40048AA1,%d0
 127         bgt             TANHHUGE
 128
 129 |-- (5/2) LOG2 < |X| < 50 LOG2,
 130 |--TANH(X) = 1 - (2/[EXP(2X)+1]). LET Y = 2|X|, SGN = SIGN(X),
 131 |--TANH(X) = SGN -      SGN*2/[EXP(Y)+1].
 132
 133         movel           X(%a6),%d0
 134         movel           %d0,SGN(%a6)
 135         andl            #0x7FFF0000,%d0
 136         addl            #0x00010000,%d0 | ...EXPO OF 2|X|
 137         movel           %d0,X(%a6)              | ...Y = 2|X|
 138         andl            #0x80000000,SGN(%a6)
 139         movel           SGN(%a6),%d0
 140         fmovex          X(%a6),%fp0             | ...Y = 2|X|
 141
 142         movel           %d1,-(%a7)
 143         clrl            %d1
 144         fmovemx %fp0-%fp0,(%a0)
 145         bsr             setox           | ...FP0 IS EXP(Y)
 146         movel           (%a7)+,%d1
 147         movel           SGN(%a6),%d0
 148         fadds           #0x3F800000,%fp0        | ...EXP(Y)+1
 149
 150         eorl            #0xC0000000,%d0 | ...-SIGN(X)*2
 151         fmoves          %d0,%fp1                | ...-SIGN(X)*2 IN SGL FMT
 152         fdivx           %fp0,%fp1               | ...-SIGN(X)2 / [EXP(Y)+1 ]
 153
 154         movel           SGN(%a6),%d0
 155         orl             #0x3F800000,%d0 | ...SGN
 156         fmoves          %d0,%fp0                | ...SGN IN SGL FMT
 157
 158         fmovel          %d1,%FPCR               |restore users exceptions
 159         faddx           %fp1,%fp0
 160
 161         bra             t_frcinx
 162
 163 TANHSM:
 164         movew           #0x0000,XDCARE(%a6)
 165
 166         fmovel          %d1,%FPCR               |restore users exceptions
 167         fmovex          X(%a6),%fp0             |last inst - possible exception set
 168
 169         bra             t_frcinx
 170
 171 TANHHUGE:
 172 |---RETURN SGN(X) - SGN(X)EPS
 173         movel           X(%a6),%d0
 174         andl            #0x80000000,%d0
 175         orl             #0x3F800000,%d0
 176         fmoves          %d0,%fp0
 177         andl            #0x80000000,%d0
 178         eorl            #0x80800000,%d0 | ...-SIGN(X)*EPS
 179
 180         fmovel          %d1,%FPCR               |restore users exceptions
 181         fadds           %d0,%fp0
 182
 183         bra             t_frcinx
 184
 185         |end