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Annotation of 43BSDTahoe/usr.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 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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