1 files changed, 83 insertions, 0 deletions
diff --git a/libm/double/cosh.c b/libm/double/cosh.c
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+/*							cosh.c
+ *
+ *	Hyperbolic cosine
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * double x, y, cosh();
+ *
+ * y = cosh( x );
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * Returns hyperbolic cosine of argument in the range MINLOG to
+ * MAXLOG.
+ *
+ * cosh(x)  =  ( exp(x) + exp(-x) )/2.
+ *
+ *
+ *
+ * ACCURACY:
+ *
+ *                      Relative error:
+ * arithmetic   domain     # trials      peak         rms
+ *    DEC       +- 88       50000       4.0e-17     7.7e-18
+ *    IEEE     +-MAXLOG     30000       2.6e-16     5.7e-17
+ *
+ *
+ * ERROR MESSAGES:
+ *
+ *   message         condition      value returned
+ * cosh overflow    |x| > MAXLOG       MAXNUM
+ *
+ *
+ */
+
+/*							cosh.c */
+
+/*
+Cephes Math Library Release 2.8:  June, 2000
+Copyright 1985, 1995, 2000 by Stephen L. Moshier
+*/
+
+#include <math.h>
+#ifdef ANSIPROT
+extern double exp ( double );
+extern int isnan ( double );
+extern int isfinite ( double );
+#else
+double exp();
+int isnan(), isfinite();
+#endif
+extern double MAXLOG, INFINITY, LOGE2;
+
+double cosh(x)
+double x;
+{
+double y;
+
+#ifdef NANS
+if( isnan(x) )
+	return(x);
+#endif
+if( x < 0 )
+	x = -x;
+if( x > (MAXLOG + LOGE2) )
+	{
+	mtherr( "cosh", OVERFLOW );
+	return( INFINITY );
+	}	
+if( x >= (MAXLOG - LOGE2) )
+	{
+	y = exp(0.5 * x);
+	y = (0.5 * y) * y;
+	return(y);
+	}
+y = exp(x);
+y = 0.5 * (y + 1.0 / y);
+return( y );
+}