root/kernel/FPU-emu/poly_sin.c

/* */

DEFINITIONS

1. poly_sine

   1 /*---------------------------------------------------------------------------+
   2  |  poly_sin.c                                                               |
   3  |                                                                           |
   4  |  Computation of an approximation of the sin function by a polynomial      |
   5  |                                                                           |
   6  | Copyright (C) 1992    W. Metzenthen, 22 Parker St, Ormond, Vic 3163,      |
   7  |                       Australia.  E-mail apm233m@vaxc.cc.monash.edu.au    |
   8  |                                                                           |
   9  |                                                                           |
  10  +---------------------------------------------------------------------------*/
  11 
  12 
  13 #include "exception.h"
  14 #include "reg_constant.h"
  15 #include "fpu_emu.h"
  16 
  17 
  18 #define HIPOWER 5
  19 static unsigned short   lterms[HIPOWER][4] =
  20         {
  21         { 0x846a, 0x42d1, 0xb544, 0x921f},
  22         { 0xe110, 0x75aa, 0xbc67, 0x1466},
  23         { 0x503d, 0xa43f, 0x83c1, 0x000a},
  24         { 0x8f9d, 0x7a19, 0x00f4, 0x0000},
  25         { 0xda03, 0x06aa, 0x0000, 0x0000},
  26         };
  27 
  28 static unsigned short   negterms[HIPOWER][4] =
  29         {
  30         { 0x95ed, 0x2df2, 0xe731, 0xa55d},
  31         { 0xd159, 0xe62b, 0xd2cc, 0x0132},
  32         { 0x6342, 0xe9fb, 0x3c60, 0x0000},
  33         { 0x6256, 0xdf5a, 0x0002, 0x0000},
  34         { 0xf279, 0x000b, 0x0000, 0x0000},
  35         };
  36 
  37 
  38 /*--- poly_sine() -----------------------------------------------------------+
  39  |                                                                           |
  40  +---------------------------------------------------------------------------*/
  41 void    poly_sine(FPU_REG *arg, FPU_REG *result)
     /*  */
  42 {
  43   short exponent;
  44   FPU_REG       Xx, Xx2, Xx4, accum, negaccum;
  45   
  46   
  47   exponent = arg->exp - EXP_BIAS;
  48   
  49   if ( arg->tag == TW_Zero )
  50     {
  51       /* Return 0.0 */
  52       reg_move(&CONST_Z, result);
  53       return;
  54     }
  55   
  56 #ifdef PARANOID
  57   if ( arg->sign != 0 ) /* Can't hack a number < 0.0 */
  58     {
  59       EXCEPTION(EX_Invalid);
  60       reg_move(&CONST_QNaN, result);
  61       return;
  62     }
  63   
  64   if ( exponent >= 0 )  /* Can't hack a number > 1.0 */
  65     {
  66       if ( (exponent == 0) && (arg->sigl == 0) && (arg->sigh == 0x80000000) )
  67         {
  68           reg_move(&CONST_1, result);
  69           return;
  70         }
  71       EXCEPTION(EX_Invalid);
  72       reg_move(&CONST_QNaN, result);
  73       return;
  74     }
  75 #endif PARANOID
  76   
  77   Xx.sigl = arg->sigl;
  78   Xx.sigh = arg->sigh;
  79   if ( exponent < -1 )
  80     {
  81       /* shift the argument right by the required places */
  82       if ( shrx(&(Xx.sigl), -1-exponent) >= 0x80000000U )
  83         (*((long long *)(&(Xx.sigl))))++;       /* round up */
  84     }
  85   
  86   mul64((long long *)&(Xx.sigl), (long long *)&(Xx.sigl),
  87         (long long *)&(Xx2.sigl));
  88   mul64((long long *)&(Xx2.sigl), (long long *)&(Xx2.sigl),
  89         (long long *)&(Xx4.sigl));
  90   
  91   /* will be a valid positive nr with expon = 0 */
  92   *(short *)&(accum.sign) = 0;
  93   accum.exp = 0;
  94 
  95   /* Do the basic fixed point polynomial evaluation */
  96   polynomial(&(accum.sigl), &(Xx4.sigl), lterms, HIPOWER-1);
  97   
  98   /* will be a valid positive nr with expon = 0 */
  99   *(short *)&(negaccum.sign) = 0;
 100   negaccum.exp = 0;
 101   
 102   /* Do the basic fixed point polynomial evaluation */
 103   polynomial(&(negaccum.sigl), &(Xx4.sigl), negterms, HIPOWER-1);
 104   mul64((long long *)&(Xx2.sigl), (long long *)&(negaccum.sigl),
 105         (long long *)&(negaccum.sigl));
 106 
 107   /* Subtract the mantissas */
 108   *((long long *)(&(accum.sigl))) -= *((long long *)(&(negaccum.sigl)));
 109   
 110   /* Convert to 64 bit signed-compatible */
 111   accum.exp = EXP_BIAS - 1 + accum.exp;
 112   
 113   *(short *)&(result->sign) = *(short *)&(accum.sign);
 114   result->exp = accum.exp;
 115   result->sigl = accum.sigl;
 116   result->sigh = accum.sigh;
 117   
 118   normalize(result);
 119 
 120   reg_mul(result, arg, result);
 121   reg_u_add(result, arg, result);
 122   
 123   /* A small overflow may be possible... but an illegal result. */
 124   if ( result->exp >= EXP_BIAS )
 125     {
 126       if (    (result->exp > EXP_BIAS) /* Larger or equal 2.0 */
 127           || (result->sigl > 1)   /* Larger than 1.0+msb */
 128           ||    (result->sigh != 0x80000000) /* Much > 1.0 */
 129           )
 130         {
 131 #ifdef DEBUGGING
 132           RE_ENTRANT_CHECK_OFF
 133           printk("\nEXP=%d, MS=%08x, LS=%08x\n", result->exp,
 134                  result->sigh, result->sigl);
 135           RE_ENTRANT_CHECK_ON
 136 #endif DEBUGGING
 137           EXCEPTION(EX_INTERNAL|0x103);
 138         }
 139       
 140 #ifdef DEBUGGING
 141       RE_ENTRANT_CHECK_OFF
 142       printk("\n***CORRECTING ILLEGAL RESULT*** in poly_sin() computation\n");
 143       printk("EXP=%d, MS=%08x, LS=%08x\n", result->exp,
 144              result->sigh, result->sigl);
 145       RE_ENTRANT_CHECK_ON
 146 #endif DEBUGGING
 147 
 148       result->sigl = 0; /* Truncate the result to 1.00 */
 149     }
 150 }

/* */