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Annotation of 43BSDReno/lib/libm/common/tan.c, revision 1.1.1.1

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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