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git-svn-id: http://svn2.nishi.boats/svn/milsko/trunk@557 b9cfdab3-6d41-4d17-bbe4-086880011989
77 lines
1.9 KiB
C
77 lines
1.9 KiB
C
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/* @(#)s_sin.c 1.3 95/01/18 */
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunSoft, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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/* sin(x)
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* Return sine function of x.
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*
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* kernel function:
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* __fdlibm_kernel_sin ... sine function on [-pi/4,pi/4]
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* __fdlibm_kernel_cos ... cose function on [-pi/4,pi/4]
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* __fdlibm_kernel_rem_pio2 ... argument reduction routine
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*
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* Method.
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* Let S,C and T denote the sin, cos and tan respectively on
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* [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
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* in [-pi/4 , +pi/4], and let n = k mod 4.
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* We have
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*
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* n sin(x) cos(x) tan(x)
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* ----------------------------------------------------------
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* 0 S C T
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* 1 C -S -1/T
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* 2 -S -C T
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* 3 -C S -1/T
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* ----------------------------------------------------------
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*
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* Special cases:
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* Let trig be any of sin, cos, or tan.
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* trig(+-INF) is NaN, with signals;
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* trig(NaN) is that NaN;
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*
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* Accuracy:
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* TRIG(x) returns trig(x) nearly rounded
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*/
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#include "math.h"
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double sin(double x) {
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double y[2], z = 0.0;
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int n, ix;
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/* High word of x. */
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ix = __HI(x);
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/* |x| ~< pi/4 */
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ix &= 0x7fffffff;
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if(ix <= 0x3fe921fb) return __fdlibm_kernel_sin(x, z, 0);
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/* sin(Inf or NaN) is NaN */
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else if(ix >= 0x7ff00000)
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return x - x;
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/* argument reduction needed */
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else {
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n = __fdlibm_rem_pio2(x, y);
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switch(n & 3) {
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case 0:
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return __fdlibm_kernel_sin(y[0], y[1], 1);
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case 1:
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return __fdlibm_kernel_cos(y[0], y[1]);
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case 2:
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return -__fdlibm_kernel_sin(y[0], y[1], 1);
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default:
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return -__fdlibm_kernel_cos(y[0], y[1]);
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}
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}
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}
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