1 files changed, 53 insertions, 0 deletions
diff --git a/src/math/s_asinh.c b/src/math/s_asinh.c
new file mode 100644
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+++ b/src/math/s_asinh.c
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+/* @(#)s_asinh.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.
+ * ====================================================
+ */
+
+/* asinh(x)
+ * Method :
+ *      Based on
+ *              asinh(x) = sign(x) * log [ |x| + sqrt(x*x+1) ]
+ *      we have
+ *      asinh(x) := x  if  1+x*x=1,
+ *               := sign(x)*(log(x)+ln2)) for large |x|, else
+ *               := sign(x)*log(2|x|+1/(|x|+sqrt(x*x+1))) if|x|>2, else
+ *               := sign(x)*log1p(|x| + x^2/(1 + sqrt(1+x^2)))
+ */
+
+#include <math.h>
+#include "math_private.h"
+
+static const double
+one =  1.00000000000000000000e+00, /* 0x3FF00000, 0x00000000 */
+ln2 =  6.93147180559945286227e-01, /* 0x3FE62E42, 0xFEFA39EF */
+huge=  1.00000000000000000000e+300;
+
+double
+asinh(double x)
+{
+        double t,w;
+        int32_t hx,ix;
+        GET_HIGH_WORD(hx,x);
+        ix = hx&0x7fffffff;
+        if(ix>=0x7ff00000) return x+x;  /* x is inf or NaN */
+        if(ix< 0x3e300000) {    /* |x|<2**-28 */
+            if(huge+x>one) return x;    /* return x inexact except 0 */
+        }
+        if(ix>0x41b00000) {     /* |x| > 2**28 */
+            w = log(fabs(x))+ln2;
+        } else if (ix>0x40000000) {     /* 2**28 > |x| > 2.0 */
+            t = fabs(x);
+            w = log(2.0*t+one/(sqrt(x*x+one)+t));
+        } else {                /* 2.0 > |x| > 2**-28 */
+            t = x*x;
+            w =log1p(fabs(x)+t/(one+sqrt(one+t)));
+        }
+        if(hx>0) return w; else return -w;
+}