lib/libm/src/k_sin.c

   1 /* @(#)k_sin.c 5.1 93/09/24 */
   2 /*
   3  * ====================================================
   4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   5  *
   6  * Developed at SunPro, a Sun Microsystems, Inc. business.
   7  * Permission to use, copy, modify, and distribute this
   8  * software is freely granted, provided that this notice
   9  * is preserved.
  10  * ====================================================
  11  *
  12  * $NetBSD: k_sin.c,v 1.11 2002/05/26 22:01:53 wiz Exp $
  13  * $DragonFly: src/lib/libm/src/k_sin.c,v 1.1 2005/07/26 21:15:20 joerg Exp $
  14  */
  15
  16 /* __kernel_sin( x, y, iy)
  17  * kernel sin function on [-pi/4, pi/4], pi/4 ~ 0.7854
  18  * Input x is assumed to be bounded by ~pi/4 in magnitude.
  19  * Input y is the tail of x.
  20  * Input iy indicates whether y is 0. (if iy=0, y assume to be 0).
  21  *
  22  * Algorithm
  23  *      1. Since sin(-x) = -sin(x), we need only to consider positive x.
  24  *      2. if x < 2^-27 (hx<0x3e400000 0), return x with inexact if x!=0.
  25  *      3. sin(x) is approximated by a polynomial of degree 13 on
  26  *         [0,pi/4]
  27  *                               3            13
  28  *              sin(x) ~ x + S1*x + ... + S6*x
  29  *         where
  30  *
  31  *      |sin(x)         2     4     6     8     10     12  |     -58
  32  *      |----- - (1+S1*x +S2*x +S3*x +S4*x +S5*x  +S6*x   )| <= 2
  33  *      |  x                                               |
  34  *
  35  *      4. sin(x+y) = sin(x) + sin'(x')*y
  36  *                  ~ sin(x) + (1-x*x/2)*y
  37  *         For better accuracy, let
  38  *                   3      2      2      2      2
  39  *              r = x *(S2+x *(S3+x *(S4+x *(S5+x *S6))))
  40  *         then                   3    2
  41  *              sin(x) = x + (S1*x + (x *(r-y/2)+y))
  42  */
  43
  44 #include <math.h>
  45 #include "math_private.h"
  46
  47 static const double
  48 half =  5.00000000000000000000e-01, /* 0x3FE00000, 0x00000000 */
  49 S1  = -1.66666666666666324348e-01, /* 0xBFC55555, 0x55555549 */
  50 S2  =  8.33333333332248946124e-03, /* 0x3F811111, 0x1110F8A6 */
  51 S3  = -1.98412698298579493134e-04, /* 0xBF2A01A0, 0x19C161D5 */
  52 S4  =  2.75573137070700676789e-06, /* 0x3EC71DE3, 0x57B1FE7D */
  53 S5  = -2.50507602534068634195e-08, /* 0xBE5AE5E6, 0x8A2B9CEB */
  54 S6  =  1.58969099521155010221e-10; /* 0x3DE5D93A, 0x5ACFD57C */
  55
  56 double
  57 __kernel_sin(double x, double y, int iy)
  58 {
  59         double z,r,v;
  60         int32_t ix;
  61         GET_HIGH_WORD(ix,x);
  62         ix &= 0x7fffffff;                       /* high word of x */
  63         if(ix<0x3e400000)                       /* |x| < 2**-27 */
  64            {if((int)x==0) return x;}            /* generate inexact */
  65         z       =  x*x;
  66         v       =  z*x;
  67         r       =  S2+z*(S3+z*(S4+z*(S5+z*S6)));
  68         if(iy==0) return x+v*(S1+z*r);
  69         else      return x-((z*(half*y-v*r)-y)-v*S1);
  70 }