1 files changed, 167 insertions, 0 deletions
diff --git a/libm/double/acosh.c b/libm/double/acosh.c
new file mode 100644
index 000000000..49d9a40e2
--- /dev/null
+++ b/libm/double/acosh.c
@@ -0,0 +1,167 @@
+/*							acosh.c
+ *
+ *	Inverse hyperbolic cosine
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * double x, y, acosh();
+ *
+ * y = acosh( x );
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * Returns inverse hyperbolic cosine of argument.
+ *
+ * If 1 <= x < 1.5, a rational approximation
+ *
+ *	sqrt(z) * P(z)/Q(z)
+ *
+ * where z = x-1, is used.  Otherwise,
+ *
+ * acosh(x)  =  log( x + sqrt( (x-1)(x+1) ).
+ *
+ *
+ *
+ * ACCURACY:
+ *
+ *                      Relative error:
+ * arithmetic   domain     # trials      peak         rms
+ *    DEC       1,3         30000       4.2e-17     1.1e-17
+ *    IEEE      1,3         30000       4.6e-16     8.7e-17
+ *
+ *
+ * ERROR MESSAGES:
+ *
+ *   message         condition      value returned
+ * acosh domain       |x| < 1            NAN
+ *
+ */
+
+/*							acosh.c	*/
+
+/*
+Cephes Math Library Release 2.8:  June, 2000
+Copyright 1984, 1995, 2000 by Stephen L. Moshier
+*/
+
+
+/* acosh(z) = sqrt(x) * R(x), z = x + 1, interval 0 < x < 0.5 */
+
+#include <math.h>
+
+#ifdef UNK
+static double P[] = {
+ 1.18801130533544501356E2,
+ 3.94726656571334401102E3,
+ 3.43989375926195455866E4,
+ 1.08102874834699867335E5,
+ 1.10855947270161294369E5
+};
+static double Q[] = {
+/* 1.00000000000000000000E0,*/
+ 1.86145380837903397292E2,
+ 4.15352677227719831579E3,
+ 2.97683430363289370382E4,
+ 8.29725251988426222434E4,
+ 7.83869920495893927727E4
+};
+#endif
+
+#ifdef DEC
+static unsigned short P[] = {
+0041755,0115055,0144002,0146444,
+0043166,0132103,0155150,0150302,
+0044006,0057360,0003021,0162753,
+0044323,0021557,0175225,0056253,
+0044330,0101771,0040046,0006636
+};
+static unsigned short Q[] = {
+/*0040200,0000000,0000000,0000000,*/
+0042072,0022467,0126670,0041232,
+0043201,0146066,0152142,0034015,
+0043750,0110257,0121165,0026100,
+0044242,0007103,0034667,0033173,
+0044231,0014576,0175573,0017472
+};
+#endif
+
+#ifdef IBMPC
+static unsigned short P[] = {
+0x59a4,0xb900,0xb345,0x405d,
+0x1a18,0x7b4d,0xd688,0x40ae,
+0x3cbd,0x00c2,0xcbde,0x40e0,
+0xab95,0xff52,0x646d,0x40fa,
+0xc1b4,0x2804,0x107f,0x40fb
+};
+static unsigned short Q[] = {
+/*0x0000,0x0000,0x0000,0x3ff0,*/
+0x0853,0xf5b7,0x44a6,0x4067,
+0x4702,0xda8c,0x3986,0x40b0,
+0xa588,0xf44e,0x1215,0x40dd,
+0xe6cf,0x6736,0x41c8,0x40f4,
+0x63e7,0xdf6f,0x232f,0x40f3
+};
+#endif
+
+#ifdef MIEEE
+static unsigned short P[] = {
+0x405d,0xb345,0xb900,0x59a4,
+0x40ae,0xd688,0x7b4d,0x1a18,
+0x40e0,0xcbde,0x00c2,0x3cbd,
+0x40fa,0x646d,0xff52,0xab95,
+0x40fb,0x107f,0x2804,0xc1b4
+};
+static unsigned short Q[] = {
+0x4067,0x44a6,0xf5b7,0x0853,
+0x40b0,0x3986,0xda8c,0x4702,
+0x40dd,0x1215,0xf44e,0xa588,
+0x40f4,0x41c8,0x6736,0xe6cf,
+0x40f3,0x232f,0xdf6f,0x63e7,
+};
+#endif
+
+#ifdef ANSIPROT
+extern double polevl ( double, void *, int );
+extern double p1evl ( double, void *, int );
+extern double log ( double );
+extern double sqrt ( double );
+#else
+double log(), sqrt(), polevl(), p1evl();
+#endif
+extern double LOGE2, INFINITY, NAN;
+
+double acosh(x)
+double x;
+{
+double a, z;
+
+if( x < 1.0 )
+	{
+	mtherr( "acosh", DOMAIN );
+	return(NAN);
+	}
+
+if( x > 1.0e8 )
+	{
+#ifdef INFINITIES
+	if( x == INFINITY )
+		return( INFINITY );
+#endif
+	return( log(x) + LOGE2 );
+	}
+
+z = x - 1.0;
+
+if( z < 0.5 )
+	{
+	a = sqrt(z) * (polevl(z, P, 4) / p1evl(z, Q, 5) );
+	return( a );
+	}
+
+a = sqrt( z*(x+1.0) );
+return( log(x + a) );
+}