usr/src/lib/libm/common/C/tan.c

   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 #pragma weak __tan = tan
  31
  32 /* INDENT OFF */
  33 /*
  34  * tan(x)
  35  * Table look-up algorithm by K.C. Ng, November, 1989.
  36  *
  37  * kernel function:
  38  *      __k_tan         ... tangent function on [-pi/4,pi/4]
  39  *      __rem_pio2      ... argument reduction routine
  40  */
  41 /* INDENT ON */
  42
  43 #include "libm.h"
  44 #include "libm_protos.h"
  45 #include <math.h>
  46
  47 double
  48 tan(double x) {
  49         double y[2], z = 0.0;
  50         int n, ix;
  51
  52         /* high word of x */
  53         ix = ((int *) &x)[HIWORD];
  54
  55         /* |x| ~< pi/4 */
  56         ix &= 0x7fffffff;
  57         if (ix <= 0x3fe921fb)
  58                 return (__k_tan(x, z, 0));
  59
  60         /* tan(Inf or NaN) is NaN */
  61         else if (ix >= 0x7ff00000) {
  62 #if defined(FPADD_TRAPS_INCOMPLETE_ON_NAN)
  63                 return (ix >= 0x7ff80000 ? x : x - x);  /* NaN */
  64                 /* assumes sparc-like QNaN */
  65 #else
  66                 return (x - x);                         /* NaN */
  67 #endif
  68         }
  69
  70         /* argument reduction needed */
  71         else {
  72                 n = __rem_pio2(x, y);
  73                 return (__k_tan(y[0], y[1], n & 1));
  74         }
  75 }