arch/m68k/fpsp040/sasin.S

   1 |
   2 |       sasin.sa 3.3 12/19/90
   3 |
   4 |       Description: The entry point sAsin computes the inverse sine of
   5 |               an input argument; sAsind 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 arcsin(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 sASIN takes approximately 310 cycles.
  19 |
  20 |       Algorithm:
  21 |
  22 |       ASIN
  23 |       1. If |X| >= 1, go to 3.
  24 |
  25 |       2. (|X| < 1) Calculate asin(X) by
  26 |               z := sqrt( [1-X][1+X] )
  27 |               asin(X) = atan( x / z ).
  28 |               Exit.
  29 |
  30 |       3. If |X| > 1, go to 5.
  31 |
  32 |       4. (|X| = 1) sgn := sign(X), return asin(X) := sgn * Pi/2. Exit.
  33 |
  34 |       5. (|X| > 1) Generate an invalid operation by 0 * infinity.
  35 |               Exit.
  36 |
  37
  38 |               Copyright (C) Motorola, Inc. 1990
  39 |                       All Rights Reserved
  40 |
  41 |       For details on the license for this file, please see the
  42 |       file, README, in this same directory.
  43
  44 |SASIN  idnt    2,1 | Motorola 040 Floating Point Software Package
  45
  46         |section        8
  47
  48 PIBY2:  .long 0x3FFF0000,0xC90FDAA2,0x2168C235,0x00000000
  49
  50         |xref   t_operr
  51         |xref   t_frcinx
  52         |xref   t_extdnrm
  53         |xref   satan
  54
  55         .global sasind
  56 sasind:
  57 |--ASIN(X) = X FOR DENORMALIZED X
  58
  59         bra             t_extdnrm
  60
  61         .global sasin
  62 sasin:
  63         fmovex          (%a0),%fp0      | ...LOAD INPUT
  64
  65         movel           (%a0),%d0
  66         movew           4(%a0),%d0
  67         andil           #0x7FFFFFFF,%d0
  68         cmpil           #0x3FFF8000,%d0
  69         bges            asinbig
  70
  71 |--THIS IS THE USUAL CASE, |X| < 1
  72 |--ASIN(X) = ATAN( X / SQRT( (1-X)(1+X) ) )
  73
  74         fmoves          #0x3F800000,%fp1
  75         fsubx           %fp0,%fp1               | ...1-X
  76         fmovemx %fp2-%fp2,-(%a7)
  77         fmoves          #0x3F800000,%fp2
  78         faddx           %fp0,%fp2               | ...1+X
  79         fmulx           %fp2,%fp1               | ...(1+X)(1-X)
  80         fmovemx (%a7)+,%fp2-%fp2
  81         fsqrtx          %fp1            | ...SQRT([1-X][1+X])
  82         fdivx           %fp1,%fp0               | ...X/SQRT([1-X][1+X])
  83         fmovemx %fp0-%fp0,(%a0)
  84         bsr             satan
  85         bra             t_frcinx
  86
  87 asinbig:
  88         fabsx           %fp0     | ...|X|
  89         fcmps           #0x3F800000,%fp0
  90         fbgt            t_operr         |cause an operr exception
  91
  92 |--|X| = 1, ASIN(X) = +- PI/2.
  93
  94         fmovex          PIBY2,%fp0
  95         movel           (%a0),%d0
  96         andil           #0x80000000,%d0 | ...SIGN BIT OF X
  97         oril            #0x3F800000,%d0 | ...+-1 IN SGL FORMAT
  98         movel           %d0,-(%sp)      | ...push SIGN(X) IN SGL-FMT
  99         fmovel          %d1,%FPCR
 100         fmuls           (%sp)+,%fp0
 101         bra             t_frcinx
 102
 103         |end