From 1077fa4d772832f77a677ce7fb7c2d513b959e3f Mon Sep 17 00:00:00 2001
From: Eric Andersen <andersen@codepoet.org>
Date: Thu, 10 May 2001 00:40:28 +0000
Subject: uClibc now has a math library.  muahahahaha!  -Erik

---
 libm/float/cbrtf.c | 119 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 119 insertions(+)
 create mode 100644 libm/float/cbrtf.c

(limited to 'libm/float/cbrtf.c')

diff --git a/libm/float/cbrtf.c b/libm/float/cbrtf.c
new file mode 100644
index 000000000..ca9b433d9
--- /dev/null
+++ b/libm/float/cbrtf.c
@@ -0,0 +1,119 @@
+/*							cbrtf.c
+ *
+ *	Cube root
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * float x, y, cbrtf();
+ *
+ * y = cbrtf( x );
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * Returns the cube root of the argument, which may be negative.
+ *
+ * Range reduction involves determining the power of 2 of
+ * the argument.  A polynomial of degree 2 applied to the
+ * mantissa, and multiplication by the cube root of 1, 2, or 4
+ * approximates the root to within about 0.1%.  Then Newton's
+ * iteration is used to converge to an accurate result.
+ *
+ *
+ *
+ * ACCURACY:
+ *
+ *                      Relative error:
+ * arithmetic   domain     # trials      peak         rms
+ *    IEEE      0,1e38      100000      7.6e-8      2.7e-8
+ *
+ */
+/*							cbrt.c  */
+
+/*
+Cephes Math Library Release 2.2:  June, 1992
+Copyright 1984, 1987, 1988, 1992 by Stephen L. Moshier
+Direct inquiries to 30 Frost Street, Cambridge, MA 02140
+*/
+
+
+#include <math.h>
+
+static float CBRT2 = 1.25992104989487316477;
+static float CBRT4 = 1.58740105196819947475;
+
+
+float frexpf(float, int *), ldexpf(float, int);
+
+float cbrtf( float xx )
+{
+int e, rem, sign;
+float x, z;
+
+x = xx;
+if( x == 0 )
+	return( 0.0 );
+if( x > 0 )
+	sign = 1;
+else
+	{
+	sign = -1;
+	x = -x;
+	}
+
+z = x;
+/* extract power of 2, leaving
+ * mantissa between 0.5 and 1
+ */
+x = frexpf( x, &e );
+
+/* Approximate cube root of number between .5 and 1,
+ * peak relative error = 9.2e-6
+ */
+x = (((-0.13466110473359520655053  * x
+      + 0.54664601366395524503440 ) * x
+      - 0.95438224771509446525043 ) * x
+      + 1.1399983354717293273738  ) * x
+      + 0.40238979564544752126924;
+
+/* exponent divided by 3 */
+if( e >= 0 )
+	{
+	rem = e;
+	e /= 3;
+	rem -= 3*e;
+	if( rem == 1 )
+		x *= CBRT2;
+	else if( rem == 2 )
+		x *= CBRT4;
+	}
+
+
+/* argument less than 1 */
+
+else
+	{
+	e = -e;
+	rem = e;
+	e /= 3;
+	rem -= 3*e;
+	if( rem == 1 )
+		x /= CBRT2;
+	else if( rem == 2 )
+		x /= CBRT4;
+	e = -e;
+	}
+
+/* multiply by power of 2 */
+x = ldexpf( x, e );
+
+/* Newton iteration */
+x -= ( x - (z/(x*x)) ) * 0.333333333333;
+
+if( sign < 0 )
+	x = -x;
+return(x);
+}
-- 
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