Initial Contributionandroid-1.0

1 files changed, 141 insertions, 0 deletions

diff --git a/libm/src/s_exp2f.c b/libm/src/s_exp2f.c
new file mode 100644
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+++ b/libm/src/s_exp2f.c
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+/*-
+ * Copyright (c) 2005 David Schultz <das@FreeBSD.ORG>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+/* __FBSDID("$FreeBSD: src/lib/msun/src/s_exp2f.c,v 1.1 2005/04/05 02:57:15 das Exp $"); */
+
+#include "math.h"
+#include "math_private.h"
+
+#define	TBLBITS	4
+#define	TBLSIZE	(1 << TBLBITS)
+
+static const float
+    huge    = 0x1p100f,
+    twom100 = 0x1p-100f,
+    redux   = 0x1.8p23f / TBLSIZE,
+    P1	    = 0x1.62e430p-1f,
+    P2	    = 0x1.ebfbe0p-3f,
+    P3	    = 0x1.c6b348p-5f,
+    P4	    = 0x1.3b2c9cp-7f;
+
+static const double exp2ft[TBLSIZE] = {
+	0x1.6a09e667f3bcdp-1,
+	0x1.7a11473eb0187p-1,
+	0x1.8ace5422aa0dbp-1,
+	0x1.9c49182a3f090p-1,
+	0x1.ae89f995ad3adp-1,
+	0x1.c199bdd85529cp-1,
+	0x1.d5818dcfba487p-1,
+	0x1.ea4afa2a490dap-1,
+	0x1.0000000000000p+0,
+	0x1.0b5586cf9890fp+0,
+	0x1.172b83c7d517bp+0,
+	0x1.2387a6e756238p+0,
+	0x1.306fe0a31b715p+0,
+	0x1.3dea64c123422p+0,
+	0x1.4bfdad5362a27p+0,
+	0x1.5ab07dd485429p+0,
+};
+	
+/*
+ * exp2f(x): compute the base 2 exponential of x
+ *
+ * Accuracy: Peak error < 0.501 ulp; location of peak: -0.030110927.
+ *
+ * Method: (equally-spaced tables)
+ *
+ *   Reduce x:
+ *     x = 2**k + y, for integer k and |y| <= 1/2.
+ *     Thus we have exp2f(x) = 2**k * exp2(y).
+ *
+ *   Reduce y:
+ *     y = i/TBLSIZE + z for integer i near y * TBLSIZE.
+ *     Thus we have exp2(y) = exp2(i/TBLSIZE) * exp2(z),
+ *     with |z| <= 2**-(TBLSIZE+1).
+ *
+ *   We compute exp2(i/TBLSIZE) via table lookup and exp2(z) via a
+ *   degree-4 minimax polynomial with maximum error under 1.4 * 2**-33.
+ *   Using double precision in the final calculation avoids roundoff error.
+ *
+ *   This method is due to Tang, but I do not use his suggested parameters:
+ *
+ *	Tang, P.  Table-driven Implementation of the Exponential Function
+ *	in IEEE Floating-Point Arithmetic.  TOMS 15(2), 144-157 (1989).
+ */
+float
+exp2f(float x)
+{
+	double tv;
+	float r, z;
+	volatile float t;	/* prevent gcc from using too much precision */
+	uint32_t hx, hr, ix, i0;
+	int32_t k;
+
+	/* Filter out exceptional cases. */
+	GET_FLOAT_WORD(hx,x);
+	ix = hx & 0x7fffffff;		/* high word of |x| */
+	if(ix >= 0x43000000) {			/* |x| >= 128 */
+		if(ix >= 0x7f800000) {
+			if ((ix & 0x7fffff) != 0 || (hx & 0x80000000) == 0)
+				return (x); 	/* x is NaN or +Inf */
+			else 
+				return (0.0);	/* x is -Inf */
+		}
+		if(x >= 0x1.0p7f)
+			return (huge * huge);	/* overflow */
+		if(x <= -0x1.2cp7f)
+			return (twom100 * twom100); /* underflow */
+	} else if (ix <= 0x33000000) {		/* |x| <= 0x1p-25 */
+		return (1.0f + x);
+	}
+
+	/* Reduce x, computing z, i0, and k. */
+	t = x + redux;
+	GET_FLOAT_WORD(i0, t);
+	i0 += TBLSIZE / 2;
+	k = (i0 >> TBLBITS) << 23;
+	i0 &= TBLSIZE - 1;
+	t -= redux;
+	z = x - t;
+
+	/* Compute r = exp2(y) = exp2ft[i0] * p(z). */
+	tv = exp2ft[i0];
+	r = tv + tv * (z * (P1 + z * (P2 + z * (P3 + z * P4))));
+
+	/* Scale by 2**(k>>23). */
+	if(k >= -125 << 23) {
+		if (k != 0) {
+			GET_FLOAT_WORD(hr, r);
+			SET_FLOAT_WORD(r, hr + k);
+		}
+		return (r);
+	} else {
+		GET_FLOAT_WORD(hr, r);
+		SET_FLOAT_WORD(r, hr + (k + (100 << 23)));
+		return (r * twom100);
+	}
+}