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Diffstat (limited to 'sysdeps/generic/tanh.c')
| -rw-r--r-- | sysdeps/generic/tanh.c | 99 |
1 files changed, 99 insertions, 0 deletions
diff --git a/sysdeps/generic/tanh.c b/sysdeps/generic/tanh.c new file mode 100644 index 0000000000..d4923b3418 --- /dev/null +++ b/sysdeps/generic/tanh.c @@ -0,0 +1,99 @@ +/* + * Copyright (c) 1985, 1993 + * The Regents of the University of California. All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * 3. All advertising materials mentioning features or use of this software + * must display the following acknowledgement: + * This product includes software developed by the University of + * California, Berkeley and its contributors. + * 4. Neither the name of the University nor the names of its contributors + * may be used to endorse or promote products derived from this software + * without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE + * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY + * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF + * SUCH DAMAGE. + */ + +#ifndef lint +static char sccsid[] = "@(#)tanh.c 8.1 (Berkeley) 6/4/93"; +#endif /* not lint */ + +/* TANH(X) + * RETURN THE HYPERBOLIC TANGENT OF X + * DOUBLE PRECISION (VAX D FORMAT 56 BITS, IEEE DOUBLE 53 BITS) + * CODED IN C BY K.C. NG, 1/8/85; + * REVISED BY K.C. NG on 2/8/85, 2/11/85, 3/7/85, 3/24/85. + * + * Required system supported functions : + * copysign(x,y) + * finite(x) + * + * Required kernel function: + * expm1(x) ...exp(x)-1 + * + * Method : + * 1. reduce x to non-negative by tanh(-x) = - tanh(x). + * 2. + * 0 < x <= 1.e-10 : tanh(x) := x + * -expm1(-2x) + * 1.e-10 < x <= 1 : tanh(x) := -------------- + * expm1(-2x) + 2 + * 2 + * 1 <= x <= 22.0 : tanh(x) := 1 - --------------- + * expm1(2x) + 2 + * 22.0 < x <= INF : tanh(x) := 1. + * + * Note: 22 was chosen so that fl(1.0+2/(expm1(2*22)+2)) == 1. + * + * Special cases: + * tanh(NaN) is NaN; + * only tanh(0)=0 is exact for finite argument. + * + * Accuracy: + * tanh(x) returns the exact hyperbolic tangent of x nealy rounded. + * In a test run with 1,024,000 random arguments on a VAX, the maximum + * observed error was 2.22 ulps (units in the last place). + */ + +double tanh(x) +double x; +{ + static double one=1.0, two=2.0, small = 1.0e-10, big = 1.0e10; + double expm1(), t, copysign(), sign; + int finite(); + +#if !defined(vax)&&!defined(tahoe) + if(x!=x) return(x); /* x is NaN */ +#endif /* !defined(vax)&&!defined(tahoe) */ + + sign=copysign(one,x); + x=copysign(x,one); + if(x < 22.0) + if( x > one ) + return(copysign(one-two/(expm1(x+x)+two),sign)); + else if ( x > small ) + {t= -expm1(-(x+x)); return(copysign(t/(two-t),sign));} + else /* raise the INEXACT flag for non-zero x */ + {big+x; return(copysign(x,sign));} + else if(finite(x)) + return (sign+1.0E-37); /* raise the INEXACT flag */ + else + return(sign); /* x is +- INF */ +} |