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Annotation of 43BSDReno/lib/libm/common/tan.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1987 Regents of the University of California.
        !             3:  * All rights reserved.
        !             4:  *
        !             5:  * Redistribution and use in source and binary forms are permitted
        !             6:  * provided that: (1) source distributions retain this entire copyright
        !             7:  * notice and comment, and (2) distributions including binaries display
        !             8:  * the following acknowledgement:  ``This product includes software
        !             9:  * developed by the University of California, Berkeley and its contributors''
        !            10:  * in the documentation or other materials provided with the distribution
        !            11:  * and in all advertising materials mentioning features or use of this
        !            12:  * software. Neither the name of the University nor the names of its
        !            13:  * contributors may be used to endorse or promote products derived
        !            14:  * from this software without specific prior written permission.
        !            15:  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
        !            16:  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
        !            17:  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
        !            18:  *
        !            19:  * All recipients should regard themselves as participants in an ongoing
        !            20:  * research project and hence should feel obligated to report their
        !            21:  * experiences (good or bad) with these elementary function codes, using
        !            22:  * the sendbug(8) program, to the authors.
        !            23:  */
        !            24: 
        !            25: #ifndef lint
        !            26: static char sccsid[] = "@(#)tan.c      5.4 (Berkeley) 6/1/90";
        !            27: #endif /* not lint */
        !            28: 
        !            29: #include "trig.h"
        !            30: double
        !            31: tan(x) 
        !            32: double x;
        !            33: {
        !            34:        double a,z,ss,cc,c;
        !            35:        int k;
        !            36: 
        !            37:        if(!finite(x))          /* tan(NaN) and tan(INF) must be NaN */
        !            38:                return x-x;
        !            39:        x = drem(x,PI);                 /* reduce x into [-PI/2, PI/2] */
        !            40:        a = copysign(x,one);            /* ... = abs(x) */
        !            41:        if (a >= PIo4) {
        !            42:                k = 1;
        !            43:                x = copysign(PIo2-a,x);
        !            44:        }
        !            45:        else {
        !            46:                k = 0;
        !            47:                if (a < small) {
        !            48:                        big+a;
        !            49:                        return x;
        !            50:                }
        !            51:        }
        !            52:        z = x*x;
        !            53:        cc = cos__C(z);
        !            54:        ss = sin__S(z);
        !            55:        z *= half;                      /* Next get c = cos(x) accurately */
        !            56:        c = (z >= thresh ? half-((z-half)-cc) : one-(z-cc));
        !            57:        if (k == 0)
        !            58:                return x+(x*(z-(cc-ss)))/c;     /* ... sin/cos */
        !            59: #ifdef national
        !            60:        else if (x == zero)
        !            61:                return copysign(fmax,x);        /* no inf on 32k */
        !            62: #endif /* national */
        !            63:        else
        !            64:                return c/(x+x*ss);              /* ... cos/sin */
        !            65: }

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