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authorEric Andersen <andersen@codepoet.org>2001-05-10 00:40:28 +0000
committerEric Andersen <andersen@codepoet.org>2001-05-10 00:40:28 +0000
commit1077fa4d772832f77a677ce7fb7c2d513b959e3f (patch)
tree579bee13fb0b58d2800206366ec2caecbb15f3fc /libm/float/tanhf.c
parent22358dd7ce7bb49792204b698f01a6f69b9c8e08 (diff)
uClibc now has a math library. muahahahaha!
-Erik
Diffstat (limited to 'libm/float/tanhf.c')
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1 files changed, 88 insertions, 0 deletions
diff --git a/libm/float/tanhf.c b/libm/float/tanhf.c
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+/* tanhf.c
+ *
+ * Hyperbolic tangent
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * float x, y, tanhf();
+ *
+ * y = tanhf( x );
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * Returns hyperbolic tangent of argument in the range MINLOG to
+ * MAXLOG.
+ *
+ * A polynomial approximation is used for |x| < 0.625.
+ * Otherwise,
+ *
+ * tanh(x) = sinh(x)/cosh(x) = 1 - 2/(exp(2x) + 1).
+ *
+ *
+ *
+ * ACCURACY:
+ *
+ * Relative error:
+ * arithmetic domain # trials peak rms
+ * IEEE -2,2 100000 1.3e-7 2.6e-8
+ *
+ */
+
+/*
+Cephes Math Library Release 2.2: June, 1992
+Copyright 1984, 1987, 1989, 1992 by Stephen L. Moshier
+Direct inquiries to 30 Frost Street, Cambridge, MA 02140
+*/
+
+/* Single precision hyperbolic tangent
+ * test interval: [-0.625, +0.625]
+ * trials: 10000
+ * peak relative error: 7.2e-8
+ * rms relative error: 2.6e-8
+ */
+#include <math.h>
+
+extern float MAXLOGF;
+
+float expf( float );
+
+float tanhf( float xx )
+{
+float x, z;
+
+if( xx < 0 )
+ x = -xx;
+else
+ x = xx;
+
+if( x > 0.5 * MAXLOGF )
+ {
+ if( xx > 0 )
+ return( 1.0 );
+ else
+ return( -1.0 );
+ }
+if( x >= 0.625 )
+ {
+ x = expf(x+x);
+ z = 1.0 - 2.0/(x + 1.0);
+ if( xx < 0 )
+ z = -z;
+ }
+else
+ {
+ z = x * x;
+ z =
+ (((( -5.70498872745E-3 * z
+ + 2.06390887954E-2) * z
+ - 5.37397155531E-2) * z
+ + 1.33314422036E-1) * z
+ - 3.33332819422E-1) * z * xx
+ + xx;
+ }
+return( z );
+}