1 files changed, 74 insertions, 0 deletions
diff --git a/src/math/cosh.c b/src/math/cosh.c
new file mode 100644
index 00000000..5f38b276
--- /dev/null
+++ b/src/math/cosh.c
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+/* origin: FreeBSD /usr/src/lib/msun/src/e_cosh.c */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunSoft, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+/* 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 "libm.h"
+
+static const double one = 1.0, half = 0.5, huge = 1.0e300;
+
+double cosh(double x)
+{
+	double t, w;
+	int32_t ix;
+
+	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 = exp(fabs(x));
+		return half*t + half/t;
+	}
+
+	/* |x| in [22, log(maxdouble)] return half*exp(|x|) */
+	if (ix < 0x40862E42)
+		return half*exp(fabs(x));
+
+	/* |x| in [log(maxdouble), overflowthresold] */
+	if (ix <= 0x408633CE)
+		return __expo2(fabs(x));
+
+	/* |x| > overflowthresold, cosh(x) overflow */
+	return huge*huge;
+}