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/double/powi.c | 186 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 186 insertions(+)
 create mode 100644 libm/double/powi.c

(limited to 'libm/double/powi.c')

diff --git a/libm/double/powi.c b/libm/double/powi.c
new file mode 100644
index 000000000..46d9a1400
--- /dev/null
+++ b/libm/double/powi.c
@@ -0,0 +1,186 @@
+/*							powi.c
+ *
+ *	Real raised to integer power
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * double x, y, powi();
+ * int n;
+ *
+ * y = powi( x, n );
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * Returns argument x raised to the nth power.
+ * The routine efficiently decomposes n as a sum of powers of
+ * two. The desired power is a product of two-to-the-kth
+ * powers of x.  Thus to compute the 32767 power of x requires
+ * 28 multiplications instead of 32767 multiplications.
+ *
+ *
+ *
+ * ACCURACY:
+ *
+ *
+ *                      Relative error:
+ * arithmetic   x domain   n domain  # trials      peak         rms
+ *    DEC       .04,26     -26,26    100000       2.7e-16     4.3e-17
+ *    IEEE      .04,26     -26,26     50000       2.0e-15     3.8e-16
+ *    IEEE        1,2    -1022,1023   50000       8.6e-14     1.6e-14
+ *
+ * Returns MAXNUM on overflow, zero on underflow.
+ *
+ */
+
+/*							powi.c	*/
+
+/*
+Cephes Math Library Release 2.8:  June, 2000
+Copyright 1984, 1995, 2000 by Stephen L. Moshier
+*/
+
+#include <math.h>
+#ifdef ANSIPROT
+extern double log ( double );
+extern double frexp ( double, int * );
+extern int signbit ( double );
+#else
+double log(), frexp();
+int signbit();
+#endif
+extern double NEGZERO, INFINITY, MAXNUM, MAXLOG, MINLOG, LOGE2;
+
+double powi( x, nn )
+double x;
+int nn;
+{
+int n, e, sign, asign, lx;
+double w, y, s;
+
+/* See pow.c for these tests.  */
+if( x == 0.0 )
+	{
+	if( nn == 0 )
+		return( 1.0 );
+	else if( nn < 0 )
+	    return( INFINITY );
+	else
+	  {
+	    if( nn & 1 )
+	      return( x );
+	    else
+	      return( 0.0 );
+	  }
+	}
+
+if( nn == 0 )
+	return( 1.0 );
+
+if( nn == -1 )
+	return( 1.0/x );
+
+if( x < 0.0 )
+	{
+	asign = -1;
+	x = -x;
+	}
+else
+	asign = 0;
+
+
+if( nn < 0 )
+	{
+	sign = -1;
+	n = -nn;
+	}
+else
+	{
+	sign = 1;
+	n = nn;
+	}
+
+/* Even power will be positive. */
+if( (n & 1) == 0 )
+	asign = 0;
+
+/* Overflow detection */
+
+/* Calculate approximate logarithm of answer */
+s = frexp( x, &lx );
+e = (lx - 1)*n;
+if( (e == 0) || (e > 64) || (e < -64) )
+	{
+	s = (s - 7.0710678118654752e-1) / (s +  7.0710678118654752e-1);
+	s = (2.9142135623730950 * s - 0.5 + lx) * nn * LOGE2;
+	}
+else
+	{
+	s = LOGE2 * e;
+	}
+
+if( s > MAXLOG )
+	{
+	mtherr( "powi", OVERFLOW );
+	y = INFINITY;
+	goto done;
+	}
+
+#if DENORMAL
+if( s < MINLOG )
+	{
+	y = 0.0;
+	goto done;
+	}
+
+/* Handle tiny denormal answer, but with less accuracy
+ * since roundoff error in 1.0/x will be amplified.
+ * The precise demarcation should be the gradual underflow threshold.
+ */
+if( (s < (-MAXLOG+2.0)) && (sign < 0) )
+	{
+	x = 1.0/x;
+	sign = -sign;
+	}
+#else
+/* do not produce denormal answer */
+if( s < -MAXLOG )
+	return(0.0);
+#endif
+
+
+/* First bit of the power */
+if( n & 1 )
+	y = x;
+		
+else
+	y = 1.0;
+
+w = x;
+n >>= 1;
+while( n )
+	{
+	w = w * w;	/* arg to the 2-to-the-kth power */
+	if( n & 1 )	/* if that bit is set, then include in product */
+		y *= w;
+	n >>= 1;
+	}
+
+if( sign < 0 )
+	y = 1.0/y;
+
+done:
+
+if( asign )
+	{
+	/* odd power of negative number */
+	if( y == 0.0 )
+		y = NEGZERO;
+	else
+		y = -y;
+	}
+return(y);
+}
-- 
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