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Annotation of coherent/b/lib/libm/sinh.c, revision 1.1.1.1

1.1       root        1: /*
                      2:  * libm/sinh.c
                      3:  * Hyperbolic sine.
                      4:  */
                      5: 
                      6: #include <math.h>
                      7: 
                      8: #if    EMU87
                      9: #include "emumath.h"
                     10: #endif
                     11: 
                     12: /*
                     13:  * To get a correct result for very small |x|,
                     14:  * the code below just returns x for |x| < THRESHOLD.
                     15:  * We can derive a theoretical value for THRESHOLD from the series:
                     16:  *     sinh(x)  = x + x^3/3! + x^5/5! + ...
                     17:  * so if |x| < sqrt(6 * DBL_EPSILON) then x^3/3! < x * DBL_EPSILON
                     18:  * and the low-order terms must be insignificant.
                     19:  * The threshold value below, arrived at empirically, is somewhat larger;
                     20:  * it is for IEEE fp, the DECVAX value must be slightly different but...
                     21:  */
                     22: #define        THRESHOLD       8.899087910006383e-6
                     23: 
                     24: double
                     25: sinh(x) double x;
                     26: {
                     27:        double r;
                     28:        register int e;
                     29: 
                     30:        if (fabs(x) < THRESHOLD)
                     31:                return x;
                     32:        /*
                     33:         * Hart (6.2.27) gives an alternative formula for |x| < 1,
                     34:         * unused here; should it be used?
                     35:         */
                     36:        e = errno;
                     37:        r = exp(x);
                     38:        errno = e;
                     39:        r = (r-1.0/r) / 2.0;
                     40:        return r;
                     41: }
                     42: 
                     43: /* end of sinh.c */

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