1 files changed, 156 insertions, 0 deletions
diff --git a/libm/float/powif.c b/libm/float/powif.c
new file mode 100644
index 000000000..d226896ba
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+++ b/libm/float/powif.c
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+/*							powif.c
+ *
+ *	Real raised to integer power
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * float x, y, powif();
+ * int n;
+ *
+ * y = powif( 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
+ *    IEEE      .04,26     -26,26    100000       1.1e-6      2.0e-7
+ *    IEEE        1,2      -128,128  100000       1.1e-5      1.0e-6
+ *
+ * Returns MAXNUMF on overflow, zero on underflow.
+ *
+ */
+
+/*							powi.c	*/
+
+/*
+Cephes Math Library Release 2.2:  June, 1992
+Copyright 1984, 1987, 1989 by Stephen L. Moshier
+Direct inquiries to 30 Frost Street, Cambridge, MA 02140
+*/
+
+#include <math.h>
+extern float MAXNUMF, MAXLOGF, MINLOGF, LOGE2F;
+
+float frexpf( float, int * );
+
+float powif( float x, int nn )
+{
+int n, e, sign, asign, lx;
+float w, y, s;
+
+if( x == 0.0 )
+	{
+	if( nn == 0 )
+		return( 1.0 );
+	else if( nn < 0 )
+		return( MAXNUMF );
+	else
+		return( 0.0 );
+	}
+
+if( nn == 0 )
+	return( 1.0 );
+
+
+if( x < 0.0 )
+	{
+	asign = -1;
+	x = -x;
+	}
+else
+	asign = 0;
+
+
+if( nn < 0 )
+	{
+	sign = -1;
+	n = -nn;
+/*
+	x = 1.0/x;
+*/
+	}
+else
+	{
+	sign = 0;
+	n = nn;
+	}
+
+/* Overflow detection */
+
+/* Calculate approximate logarithm of answer */
+s = frexpf( 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 * LOGE2F;
+	}
+else
+	{
+	s = LOGE2F * e;
+	}
+
+if( s > MAXLOGF )
+	{
+	mtherr( "powi", OVERFLOW );
+	y = MAXNUMF;
+	goto done;
+	}
+
+if( s < MINLOGF )
+	return(0.0);
+
+/* 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 < (-MAXLOGF+2.0) )
+	{
+	x = 1.0/x;
+	sign = 0;
+	}
+
+/* First bit of the power */
+if( n & 1 )
+	y = x;
+		
+else
+	{
+	y = 1.0;
+	asign = 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;
+	}
+
+
+done:
+
+if( asign )
+	y = -y; /* odd power of negative number */
+if( sign )
+	y = 1.0/y;
+return(y);
+}