1 files changed, 116 insertions, 0 deletions
diff --git a/libm/float/exp2f.c b/libm/float/exp2f.c
new file mode 100644
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+/*							exp2f.c
+ *
+ *	Base 2 exponential function
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * float x, y, exp2f();
+ *
+ * y = exp2f( x );
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * Returns 2 raised to the x power.
+ *
+ * Range reduction is accomplished by separating the argument
+ * into an integer k and fraction f such that
+ *     x    k  f
+ *    2  = 2  2.
+ *
+ * A polynomial approximates 2**x in the basic range [-0.5, 0.5].
+ *
+ *
+ * ACCURACY:
+ *
+ *                      Relative error:
+ * arithmetic   domain     # trials      peak         rms
+ *    IEEE     -127,+127    100000      1.7e-7      2.8e-8
+ *
+ *
+ * See exp.c for comments on error amplification.
+ *
+ *
+ * ERROR MESSAGES:
+ *
+ *   message         condition      value returned
+ * exp underflow    x < -MAXL2        0.0
+ * exp overflow     x > MAXL2         MAXNUMF
+ *
+ * For IEEE arithmetic, MAXL2 = 127.
+ */
+
+
+/*
+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 char fname[] = {"exp2f"};
+
+static float P[] = {
+ 1.535336188319500E-004,
+ 1.339887440266574E-003,
+ 9.618437357674640E-003,
+ 5.550332471162809E-002,
+ 2.402264791363012E-001,
+ 6.931472028550421E-001
+};
+#define MAXL2 127.0
+#define MINL2 -127.0
+
+
+
+extern float MAXNUMF;
+
+float polevlf(float, float *, int), floorf(float), ldexpf(float, int);
+
+float exp2f( float xx )
+{
+float x, px;
+int i0;
+
+x = xx;
+if( x > MAXL2)
+	{
+	mtherr( fname, OVERFLOW );
+	return( MAXNUMF );
+	}
+
+if( x < MINL2 )
+	{
+	mtherr( fname, UNDERFLOW );
+	return(0.0);
+	}
+
+/* The following is necessary because range reduction blows up: */
+if( x == 0 )
+	return(1.0);
+
+/* separate into integer and fractional parts */
+px = floorf(x);
+i0 = px;
+x = x - px;
+
+if( x > 0.5 )
+	{
+	i0 += 1;
+	x -= 1.0;
+	}
+
+/* rational approximation
+ * exp2(x) = 1.0 +  xP(x)
+ */
+px = 1.0 + x * polevlf( x, P, 5 );
+
+/* scale by power of 2 */
+px = ldexpf( px, i0 );
+return(px);
+}