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[/] [openrisc/] [trunk/] [gnu-old/] [newlib-1.17.0/] [newlib/] [libm/] [math/] [s_cos.c] - Blame information for rev 825

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1 148 jeremybenn
 
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/* @(#)s_cos.c 5.1 93/09/24 */
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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 SunPro, 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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/* cos(x)
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 * Return cosine function of x.
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 *
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 * kernel function:
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 *      __kernel_sin            ... sine function on [-pi/4,pi/4]
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 *      __kernel_cos            ... cosine function on [-pi/4,pi/4]
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 *      __ieee754_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 "fdlibm.h"
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#ifndef _DOUBLE_IS_32BITS
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#ifdef __STDC__
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        double cos(double x)
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#else
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        double cos(x)
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        double x;
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#endif
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{
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        double y[2],z=0.0;
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        __int32_t n,ix;
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    /* High word of x. */
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        GET_HIGH_WORD(ix,x);
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    /* |x| ~< pi/4 */
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        ix &= 0x7fffffff;
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        if(ix <= 0x3fe921fb) return __kernel_cos(x,z);
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    /* cos(Inf or NaN) is NaN */
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        else if (ix>=0x7ff00000) return x-x;
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    /* argument reduction needed */
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        else {
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            n = __ieee754_rem_pio2(x,y);
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            switch(n&3) {
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                case 0: return  __kernel_cos(y[0],y[1]);
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                case 1: return -__kernel_sin(y[0],y[1],1);
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                case 2: return -__kernel_cos(y[0],y[1]);
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                default:
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                        return  __kernel_sin(y[0],y[1],1);
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            }
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        }
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}
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#endif /* _DOUBLE_IS_32BITS */

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