root/drivers/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) 1992,1993                                                   |
   7  |                       W. Metzenthen, 22 Parker St, Ormond, Vic 3163,      |
   8  |                       Australia.  E-mail   billm@vaxc.cc.monash.edu.au    |
   9  |                                                                           |
  10  |                                                                           |
  11  +---------------------------------------------------------------------------*/
  12 
  13 
  14 #include "exception.h"
  15 #include "reg_constant.h"
  16 #include "fpu_emu.h"
  17 #include "control_w.h"
  18 
  19 
  20 #define HIPOWER 5
  21 static unsigned short const     lterms[HIPOWER][4] =
  22         {
  23         { 0x846a, 0x42d1, 0xb544, 0x921f},
  24         { 0xe110, 0x75aa, 0xbc67, 0x1466},
  25         { 0x503d, 0xa43f, 0x83c1, 0x000a},
  26         { 0x8f9d, 0x7a19, 0x00f4, 0x0000},
  27         { 0xda03, 0x06aa, 0x0000, 0x0000},
  28         };
  29 
  30 static unsigned short const     negterms[HIPOWER][4] =
  31         {
  32         { 0x95ed, 0x2df2, 0xe731, 0xa55d},
  33         { 0xd159, 0xe62b, 0xd2cc, 0x0132},
  34         { 0x6342, 0xe9fb, 0x3c60, 0x0000},
  35         { 0x6256, 0xdf5a, 0x0002, 0x0000},
  36         { 0xf279, 0x000b, 0x0000, 0x0000},
  37         };
  38 
  39 
  40 /*--- poly_sine() -----------------------------------------------------------+
  41  |                                                                           |
  42  +---------------------------------------------------------------------------*/
  43 void    poly_sine(FPU_REG const *arg, FPU_REG *result)
     /*  */
  44 {
  45   short exponent;
  46   FPU_REG       fixed_arg, arg_sqrd, arg_to_4, accum, negaccum;
  47   
  48   
  49   exponent = arg->exp - EXP_BIAS;
  50   
  51   if ( arg->tag == TW_Zero )
  52     {
  53       /* Return 0.0 */
  54       reg_move(&CONST_Z, result);
  55       return;
  56     }
  57   
  58 #ifdef PARANOID
  59   if ( arg->sign != 0 ) /* Can't hack a number < 0.0 */
  60     {
  61       EXCEPTION(EX_Invalid);
  62       reg_move(&CONST_QNaN, result);
  63       return;
  64     }
  65   
  66   if ( exponent >= 0 )  /* Can't hack a number > 1.0 */
  67     {
  68       if ( (exponent == 0) && (arg->sigl == 0) && (arg->sigh == 0x80000000) )
  69         {
  70           reg_move(&CONST_1, result);
  71           return;
  72         }
  73       EXCEPTION(EX_Invalid);
  74       reg_move(&CONST_QNaN, result);
  75       return;
  76     }
  77 #endif PARANOID
  78   
  79   fixed_arg.sigl = arg->sigl;
  80   fixed_arg.sigh = arg->sigh;
  81   if ( exponent < -1 )
  82     {
  83       /* shift the argument right by the required places */
  84       if ( shrx(&(fixed_arg.sigl), -1-exponent) >= 0x80000000U )
  85         significand(&fixed_arg)++;      /* round up */
  86     }
  87   
  88   mul64(&significand(&fixed_arg), &significand(&fixed_arg),
  89         &significand(&arg_sqrd));
  90   mul64(&significand(&arg_sqrd), &significand(&arg_sqrd),
  91         &significand(&arg_to_4));
  92   
  93   /* will be a valid positive nr with expon = 0 */
  94   *(short *)&(accum.sign) = 0;
  95   accum.exp = 0;
  96 
  97   /* Do the basic fixed point polynomial evaluation */
  98   polynomial(&(accum.sigl), &(arg_to_4.sigl), lterms, HIPOWER-1);
  99   
 100   /* will be a valid positive nr with expon = 0 */
 101   *(short *)&(negaccum.sign) = 0;
 102   negaccum.exp = 0;
 103   
 104   /* Do the basic fixed point polynomial evaluation */
 105   polynomial(&(negaccum.sigl), &(arg_to_4.sigl), negterms, HIPOWER-1);
 106   mul64(&significand(&arg_sqrd), &significand(&negaccum),
 107         &significand(&negaccum));
 108 
 109   /* Subtract the mantissas */
 110   significand(&accum) -= significand(&negaccum);
 111   
 112   /* Convert to 64 bit signed-compatible */
 113   accum.exp = EXP_BIAS - 1 + accum.exp;
 114 
 115   reg_move(&accum, result);
 116 
 117   normalize(result);
 118 
 119   reg_mul(result, arg, result, FULL_PRECISION);
 120   reg_u_add(result, arg, result, FULL_PRECISION);
 121   
 122   if ( result->exp >= EXP_BIAS )
 123     {
 124       /* A small overflow may be possible... but an illegal result. */
 125       if (    (result->exp > EXP_BIAS) /* Larger or equal 2.0 */
 126           || (result->sigl > 1)   /* Larger than 1.0+msb */
 127           ||    (result->sigh != 0x80000000) /* Much > 1.0 */
 128           )
 129         {
 130 #ifdef DEBUGGING
 131           RE_ENTRANT_CHECK_OFF
 132           printk("\nEXP=%d, MS=%08x, LS=%08x\n", result->exp,
 133                  result->sigh, result->sigl);
 134           RE_ENTRANT_CHECK_ON
 135 #endif DEBUGGING
 136           EXCEPTION(EX_INTERNAL|0x103);
 137         }
 138       
 139 #ifdef DEBUGGING
 140       RE_ENTRANT_CHECK_OFF
 141       printk("\n***CORRECTING ILLEGAL RESULT*** in poly_sin() computation\n");
 142       printk("EXP=%d, MS=%08x, LS=%08x\n", result->exp,
 143              result->sigh, result->sigl);
 144       RE_ENTRANT_CHECK_ON
 145 #endif DEBUGGING
 146 
 147       result->sigl = 0; /* Truncate the result to 1.00 */
 148     }
 149 
 150 }

/* */