1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21 
  22 /*
  23  * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
  24  */
  25 /*
  26  * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
  27  * Use is subject to license terms.
  28  */
  29 
  30 /*
  31  * long double sinpil(long double x),
  32  * return long double precision sinl(pi*x).
  33  *
  34  * Algorithm, 10/17/2002, K.C. Ng
  35  * ------------------------------
  36  * Let y = |4x|, z = floor(y), and n = (int)(z mod 8.0) (displayed in binary).
  37  *      1. If y == z, then x is a multiple of pi/4. Return the following values:
  38  *             ---------------------------------------------------
  39  *               n  x mod 2    sin(x*pi)    cos(x*pi)   tan(x*pi)
  40  *             ---------------------------------------------------
  41  *              000  0.00       +0 ___       +1 ___      +0
  42  *              001  0.25       +\/0.5       +\/0.5      +1
  43  *              010  0.50       +1 ___       +0 ___      +inf
  44  *              011  0.75       +\/0.5       -\/0.5      -1
  45  *              100  1.00       -0 ___       -1 ___      +0
  46  *              101  1.25       -\/0.5       -\/0.5      +1
  47  *              110  1.50       -1 ___       -0 ___      +inf
  48  *              111  1.75       -\/0.5       +\/0.5      -1
  49  *             ---------------------------------------------------
  50  *      2. Otherwise,
  51  *             ---------------------------------------------------
  52  *               n     t        sin(x*pi)    cos(x*pi)   tan(x*pi)
  53  *             ---------------------------------------------------
  54  *              000  (y-z)/4     sinpi(t)     cospi(t)    tanpi(t)
  55  *              001  (z+1-y)/4   cospi(t)     sinpi(t)    1/tanpi(t)
  56  *              010  (y-z)/4     cospi(t)    -sinpi(t)   -1/tanpi(t)
  57  *              011  (z+1-y)/4   sinpi(t)    -cospi(t)   -tanpi(t)
  58  *              100  (y-z)/4    -sinpi(t)    -cospi(t)    tanpi(t)
  59  *              101  (z+1-y)/4  -cospi(t)    -sinpi(t)    1/tanpi(t)
  60  *              110  (y-z)/4    -cospi(t)     sinpi(t)   -1/tanpi(t)
  61  *              111  (z+1-y)/4  -sinpi(t)     cospi(t)   -tanpi(t)
  62  *             ---------------------------------------------------
  63  *
  64  * NOTE. This program compute sinpi/cospi(t<0.25) by __k_sin/cos(pi*t, 0.0).
  65  * This will return a result with error slightly more than one ulp (but less
  66  * than 2 ulp). If one wants accurate result,  one may break up pi*t in
  67  * high (tpi_h) and low (tpi_l) parts and call __k_sin/cos(tip_h, tip_lo)
  68  * instead.
  69  */
  70 
  71 #include "libm.h"
  72 #include "longdouble.h"
  73 
  74 #define I(q, m) ((int *) &(q))[m]
  75 #define U(q, m) ((unsigned *) &(q))[m]
  76 #if defined(__LITTLE_ENDIAN) || defined(__x86)
  77 #define LDBL_MOST_SIGNIF_I(ld)  ((I(ld, 2) << 16) | (0xffff & (I(ld, 1) >> 15)))
  78 #define LDBL_LEAST_SIGNIF_U(ld) U(ld, 0)
  79 #define PREC    64
  80 #define PRECM1  63
  81 #define PRECM2  62
  82 static const long double twoPRECM2 = 9.223372036854775808000000000000000e+18L;
  83 #else
  84 #define LDBL_MOST_SIGNIF_I(ld)  I(ld, 0)
  85 #define LDBL_LEAST_SIGNIF_U(ld) U(ld, sizeof (long double) / sizeof (int) - 1)
  86 #define PREC    113
  87 #define PRECM1  112
  88 #define PRECM2  111
  89 static const long double twoPRECM2 = 5.192296858534827628530496329220096e+33L;
  90 #endif
  91 
  92 static const long double
  93 zero    = 0.0L,
  94 quater  = 0.25L,
  95 one     = 1.0L,
  96 pi      = 3.141592653589793238462643383279502884197e+0000L,
  97 sqrth   = 0.707106781186547524400844362104849039284835937688474,
  98 tiny    = 1.0e-100;
  99 
 100 long double
 101 sinpil(long double x) {
 102         long double y, z, t;
 103         int hx, n, k;
 104         unsigned lx;
 105 
 106         hx = LDBL_MOST_SIGNIF_I(x);
 107         lx = LDBL_LEAST_SIGNIF_U(x);
 108         k = ((hx & 0x7fff0000) >> 16) - 0x3fff;
 109         if (k >= PRECM2) {           /* |x| >= 2**(Prec-2) */
 110                 if (k >= 16384)
 111                         y = x - x;
 112                 else {
 113                         if (k >= PREC)
 114                                 y = zero;
 115                         else if (k == PRECM1)
 116                                 y = (lx & 1) == 0 ? zero: -zero;
 117                         else {  /* k = Prec - 2 */
 118                                 y = (lx & 1) == 0 ? zero : one;
 119                                 if ((lx & 2) != 0)
 120                                         y = -y;
 121                         }
 122                 }
 123         } else if (k < -2)   /* |x| < 0.25 */
 124                 y = __k_sinl(pi * fabsl(x), zero);
 125         else {
 126                 /* y = |4x|, z = floor(y), and n = (int)(z mod 8.0) */
 127                 y = 4.0L * fabsl(x);
 128                 if (k < PRECM2) {
 129                         z = y + twoPRECM2;
 130                         n = LDBL_LEAST_SIGNIF_U(z) & 7;     /* 3 LSb of z */
 131                         t = z - twoPRECM2;
 132                         k = 0;
 133                         if (t == y)
 134                                 k = 1;
 135                         else if (t > y) {
 136                                 n -= 1;
 137                                 t = quater + (y - t) * quater;
 138                         } else
 139                                 t = (y - t) * quater;
 140                 } else {        /* k = Prec-3 */
 141                         n = LDBL_LEAST_SIGNIF_U(y) & 7;     /* 3 LSb of z */
 142                         k = 1;
 143                 }
 144                 if (k) {        /* x = N/4 */
 145                         if ((n & 1) != 0)
 146                                 y = sqrth + tiny;
 147                         else
 148                                 y = (n & 2) == 0 ? zero : one;
 149                         if ((n & 4) != 0)
 150                                 y = -y;
 151                 } else {
 152                         if ((n & 1) != 0)
 153                                 t = quater - t;
 154                         if (((n + (n & 1)) & 2) == 0)
 155                                 y = __k_sinl(pi * t, zero);
 156                         else
 157                                 y = __k_cosl(pi * t, zero);
 158                         if ((n & 4) != 0)
 159                                 y = -y;
 160                 }
 161         }
 162         return (hx >= 0 ? y : -y);
 163 }
 164 #undef U
 165 #undef LDBL_LEAST_SIGNIF_U
 166 #undef I
 167 #undef LDBL_MOST_SIGNIF_I