1 files changed, 59 insertions, 0 deletions
diff --git a/src/math/e_acosh.c b/src/math/e_acosh.c
new file mode 100644
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--- /dev/null
+++ b/src/math/e_acosh.c
@@ -0,0 +1,59 @@
+
+/* @(#)e_acosh.c 1.3 95/01/18 */
+/*
+ * ====================================================
+ * 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.
+ * ====================================================
+ *
+ */
+
+/* acosh(x)
+ * Method :
+ *      Based on 
+ *              acosh(x) = log [ x + sqrt(x*x-1) ]
+ *      we have
+ *              acosh(x) := log(x)+ln2, if x is large; else
+ *              acosh(x) := log(2x-1/(sqrt(x*x-1)+x)) if x>2; else
+ *              acosh(x) := log1p(t+sqrt(2.0*t+t*t)); where t=x-1.
+ *
+ * Special cases:
+ *      acosh(x) is NaN with signal if x<1.
+ *      acosh(NaN) is NaN without signal.
+ */
+
+#include <math.h>
+#include "math_private.h"
+
+static const double
+one     = 1.0,
+ln2     = 6.93147180559945286227e-01;  /* 0x3FE62E42, 0xFEFA39EF */
+
+double
+acosh(double x)
+{
+        double t;
+        int32_t hx;
+        uint32_t lx;
+        EXTRACT_WORDS(hx,lx,x);
+        if(hx<0x3ff00000) {             /* x < 1 */
+            return (x-x)/(x-x);
+        } else if(hx >=0x41b00000) {    /* x > 2**28 */
+            if(hx >=0x7ff00000) {       /* x is inf of NaN */
+                return x+x;
+            } else 
+                return log(x)+ln2;    /* acosh(huge)=log(2x) */
+        } else if(((hx-0x3ff00000)|lx)==0) {
+            return 0.0;                 /* acosh(1) = 0 */
+        } else if (hx > 0x40000000) {   /* 2**28 > x > 2 */
+            t=x*x;
+            return log(2.0*x-one/(x+sqrt(t-one)));
+        } else {                        /* 1<x<2 */
+            t = x-one;
+            return log1p(t+sqrt(2.0*t+t*t));
+        }
+}