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Annotation of 43BSDTahoe/usr.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 the above copyright notice and this paragraph are
        !             7:  * duplicated in all such forms and that any documentation,
        !             8:  * advertising materials, and other materials related to such
        !             9:  * distribution and use acknowledge that the software was developed
        !            10:  * by the University of California, Berkeley.  The name of the
        !            11:  * University may not be used to endorse or promote products derived
        !            12:  * from this software without specific prior written permission.
        !            13:  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
        !            14:  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
        !            15:  * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
        !            16:  *
        !            17:  * All recipients should regard themselves as participants in an ongoing
        !            18:  * research project and hence should feel obligated to report their
        !            19:  * experiences (good or bad) with these elementary function codes, using
        !            20:  * the sendbug(8) program, to the authors.
        !            21:  */
        !            22: 
        !            23: #ifndef lint
        !            24: static char sccsid[] = "@(#)tan.c      5.3 (Berkeley) 6/30/88";
        !            25: #endif /* not lint */
        !            26: 
        !            27: #include "trig.h"
        !            28: double
        !            29: tan(x) 
        !            30: double x;
        !            31: {
        !            32:        double a,z,ss,cc,c;
        !            33:        int k;
        !            34: 
        !            35:        if(!finite(x))          /* tan(NaN) and tan(INF) must be NaN */
        !            36:                return x-x;
        !            37:        x = drem(x,PI);                 /* reduce x into [-PI/2, PI/2] */
        !            38:        a = copysign(x,one);            /* ... = abs(x) */
        !            39:        if (a >= PIo4) {
        !            40:                k = 1;
        !            41:                x = copysign(PIo2-a,x);
        !            42:        }
        !            43:        else {
        !            44:                k = 0;
        !            45:                if (a < small) {
        !            46:                        big+a;
        !            47:                        return x;
        !            48:                }
        !            49:        }
        !            50:        z = x*x;
        !            51:        cc = cos__C(z);
        !            52:        ss = sin__S(z);
        !            53:        z *= half;                      /* Next get c = cos(x) accurately */
        !            54:        c = (z >= thresh ? half-((z-half)-cc) : one-(z-cc));
        !            55:        if (k == 0)
        !            56:                return x+(x*(z-(cc-ss)))/c;     /* ... sin/cos */
        !            57: #ifdef national
        !            58:        else if (x == zero)
        !            59:                return copysign(fmax,x);        /* no inf on 32k */
        !            60: #endif /* national */
        !            61:        else
        !            62:                return c/(x+x*ss);              /* ... cos/sin */
        !            63: }

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