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authorEric Andersen <andersen@codepoet.org>2001-11-22 14:04:29 +0000
committerEric Andersen <andersen@codepoet.org>2001-11-22 14:04:29 +0000
commit7ce331c01ce6eb7b3f5c715a38a24359da9c6ee2 (patch)
tree3a7e8476e868ae15f4da1b7ce26b2db6f434468c /libm/e_cosh.c
parentc117dd5fb183afb1a4790a6f6110d88704be6bf8 (diff)
Totally rework the math library, this time based on the MacOs X
math library (which is itself based on the math lib from FreeBSD). -Erik
Diffstat (limited to 'libm/e_cosh.c')
-rw-r--r--libm/e_cosh.c93
1 files changed, 93 insertions, 0 deletions
diff --git a/libm/e_cosh.c b/libm/e_cosh.c
new file mode 100644
index 000000000..3f9ed63b4
--- /dev/null
+++ b/libm/e_cosh.c
@@ -0,0 +1,93 @@
+/* @(#)e_cosh.c 5.1 93/09/24 */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunPro, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+
+#if defined(LIBM_SCCS) && !defined(lint)
+static char rcsid[] = "$NetBSD: e_cosh.c,v 1.7 1995/05/10 20:44:58 jtc Exp $";
+#endif
+
+/* __ieee754_cosh(x)
+ * Method :
+ * mathematically cosh(x) if defined to be (exp(x)+exp(-x))/2
+ * 1. Replace x by |x| (cosh(x) = cosh(-x)).
+ * 2.
+ * [ exp(x) - 1 ]^2
+ * 0 <= x <= ln2/2 : cosh(x) := 1 + -------------------
+ * 2*exp(x)
+ *
+ * exp(x) + 1/exp(x)
+ * ln2/2 <= x <= 22 : cosh(x) := -------------------
+ * 2
+ * 22 <= x <= lnovft : cosh(x) := exp(x)/2
+ * lnovft <= x <= ln2ovft: cosh(x) := exp(x/2)/2 * exp(x/2)
+ * ln2ovft < x : cosh(x) := huge*huge (overflow)
+ *
+ * Special cases:
+ * cosh(x) is |x| if x is +INF, -INF, or NaN.
+ * only cosh(0)=1 is exact for finite x.
+ */
+
+#include "math.h"
+#include "math_private.h"
+
+#ifdef __STDC__
+static const double one = 1.0, half=0.5, huge = 1.0e300;
+#else
+static double one = 1.0, half=0.5, huge = 1.0e300;
+#endif
+
+#ifdef __STDC__
+ double __ieee754_cosh(double x)
+#else
+ double __ieee754_cosh(x)
+ double x;
+#endif
+{
+ double t,w;
+ int32_t ix;
+ u_int32_t lx;
+
+ /* High word of |x|. */
+ GET_HIGH_WORD(ix,x);
+ ix &= 0x7fffffff;
+
+ /* x is INF or NaN */
+ if(ix>=0x7ff00000) return x*x;
+
+ /* |x| in [0,0.5*ln2], return 1+expm1(|x|)^2/(2*exp(|x|)) */
+ if(ix<0x3fd62e43) {
+ t = expm1(fabs(x));
+ w = one+t;
+ if (ix<0x3c800000) return w; /* cosh(tiny) = 1 */
+ return one+(t*t)/(w+w);
+ }
+
+ /* |x| in [0.5*ln2,22], return (exp(|x|)+1/exp(|x|)/2; */
+ if (ix < 0x40360000) {
+ t = __ieee754_exp(fabs(x));
+ return half*t+half/t;
+ }
+
+ /* |x| in [22, log(maxdouble)] return half*exp(|x|) */
+ if (ix < 0x40862E42) return half*__ieee754_exp(fabs(x));
+
+ /* |x| in [log(maxdouble), overflowthresold] */
+ GET_LOW_WORD(lx,x);
+ if (ix<0x408633CE ||
+ (ix==0x408633ce)&&(lx<=(u_int32_t)0x8fb9f87d)) {
+ w = __ieee754_exp(half*fabs(x));
+ t = half*w;
+ return t*w;
+ }
+
+ /* |x| > overflowthresold, cosh(x) overflow */
+ return huge*huge;
+}