/* Support signaling NaNs. */
#define WANT_SNAN 0
+#ifndef TOINT_INTRINSICS
+#define TOINT_INTRINSICS 0
+#endif
+
+#if TOINT_INTRINSICS
+/* Round x to nearest int in all rounding modes, ties have to be rounded
+ consistently with converttoint so the results match. If the result
+ would be outside of [-2^31, 2^31-1] then the semantics is unspecified. */
+static double_t roundtoint(double_t);
+
+/* Convert x to nearest int in all rounding modes, ties have to be rounded
+ consistently with roundtoint. If the result is not representible in an
+ int32_t then the semantics is unspecified. */
+static int32_t converttoint(double_t);
+#endif
+
/* Helps static branch prediction so hot path can be better optimized. */
#ifdef __GNUC__
#define predict_true(x) __builtin_expect(!!(x), 1)
-/* origin: FreeBSD /usr/src/lib/msun/src/s_exp2f.c */
-/*-
- * 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.
+/*
+ * Single-precision 2^x function.
*
- * 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.
+ * Copyright (c) 2017-2018, Arm Limited.
+ * SPDX-License-Identifier: MIT
*/
+#include <math.h>
+#include <stdint.h>
#include "libm.h"
+#include "exp2f_data.h"
-#define TBLSIZE 16
+/*
+EXP2F_TABLE_BITS = 5
+EXP2F_POLY_ORDER = 3
-static const float
-redux = 0x1.8p23f / TBLSIZE,
-P1 = 0x1.62e430p-1f,
-P2 = 0x1.ebfbe0p-3f,
-P3 = 0x1.c6b348p-5f,
-P4 = 0x1.3b2c9cp-7f;
+ULP error: 0.502 (nearest rounding.)
+Relative error: 1.69 * 2^-34 in [-1/64, 1/64] (before rounding.)
+Wrong count: 168353 (all nearest rounding wrong results with fma.)
+Non-nearest ULP error: 1 (rounded ULP error)
+*/
-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,
-};
+#define N (1 << EXP2F_TABLE_BITS)
+#define T __exp2f_data.tab
+#define C __exp2f_data.poly
+#define SHIFT __exp2f_data.shift_scaled
+
+static inline uint32_t top12(float x)
+{
+ return asuint(x) >> 20;
+}
-/*
- * 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 = 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 for everything except the reduction makes
- * roundoff error insignificant and simplifies the scaling step.
- *
- * 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_t t, r, z;
- union {float f; uint32_t i;} u = {x};
- union {double f; uint64_t i;} uk;
- uint32_t ix, i0, k;
+ uint32_t abstop;
+ uint64_t ki, t;
+ double_t kd, xd, z, r, r2, y, s;
- /* Filter out exceptional cases. */
- ix = u.i & 0x7fffffff;
- if (ix > 0x42fc0000) { /* |x| > 126 */
- if (ix > 0x7f800000) /* NaN */
- return x;
- if (u.i >= 0x43000000 && u.i < 0x80000000) { /* x >= 128 */
- x *= 0x1p127f;
- return x;
- }
- if (u.i >= 0x80000000) { /* x < -126 */
- if (u.i >= 0xc3160000 || (u.i & 0x0000ffff))
- FORCE_EVAL(-0x1p-149f/x);
- if (u.i >= 0xc3160000) /* x <= -150 */
- return 0;
- }
- } else if (ix <= 0x33000000) { /* |x| <= 0x1p-25 */
- return 1.0f + x;
+ xd = (double_t)x;
+ abstop = top12(x) & 0x7ff;
+ if (predict_false(abstop >= top12(128.0f))) {
+ /* |x| >= 128 or x is nan. */
+ if (asuint(x) == asuint(-INFINITY))
+ return 0.0f;
+ if (abstop >= top12(INFINITY))
+ return x + x;
+ if (x > 0.0f)
+ return __math_oflowf(0);
+ if (x <= -150.0f)
+ return __math_uflowf(0);
}
- /* Reduce x, computing z, i0, and k. */
- u.f = x + redux;
- i0 = u.i;
- i0 += TBLSIZE / 2;
- k = i0 / TBLSIZE;
- uk.i = (uint64_t)(0x3ff + k)<<52;
- i0 &= TBLSIZE - 1;
- u.f -= redux;
- z = x - u.f;
- /* Compute r = exp2(y) = exp2ft[i0] * p(z). */
- r = exp2ft[i0];
- t = r * z;
- r = r + t * (P1 + z * P2) + t * (z * z) * (P3 + z * P4);
+ /* x = k/N + r with r in [-1/(2N), 1/(2N)] and int k. */
+ kd = eval_as_double(xd + SHIFT);
+ ki = asuint64(kd);
+ kd -= SHIFT; /* k/N for int k. */
+ r = xd - kd;
- /* Scale by 2**k */
- return r * uk.f;
+ /* exp2(x) = 2^(k/N) * 2^r ~= s * (C0*r^3 + C1*r^2 + C2*r + 1) */
+ t = T[ki % N];
+ t += ki << (52 - EXP2F_TABLE_BITS);
+ s = asdouble(t);
+ z = C[0] * r + C[1];
+ r2 = r * r;
+ y = C[2] * r + 1;
+ y = z * r2 + y;
+ y = y * s;
+ return eval_as_float(y);
}
--- /dev/null
+/*
+ * Shared data between expf, exp2f and powf.
+ *
+ * Copyright (c) 2017-2018, Arm Limited.
+ * SPDX-License-Identifier: MIT
+ */
+
+#include "exp2f_data.h"
+
+#define N (1 << EXP2F_TABLE_BITS)
+
+const struct exp2f_data __exp2f_data = {
+ /* tab[i] = uint(2^(i/N)) - (i << 52-BITS)
+ used for computing 2^(k/N) for an int |k| < 150 N as
+ double(tab[k%N] + (k << 52-BITS)) */
+ .tab = {
+0x3ff0000000000000, 0x3fefd9b0d3158574, 0x3fefb5586cf9890f, 0x3fef9301d0125b51,
+0x3fef72b83c7d517b, 0x3fef54873168b9aa, 0x3fef387a6e756238, 0x3fef1e9df51fdee1,
+0x3fef06fe0a31b715, 0x3feef1a7373aa9cb, 0x3feedea64c123422, 0x3feece086061892d,
+0x3feebfdad5362a27, 0x3feeb42b569d4f82, 0x3feeab07dd485429, 0x3feea47eb03a5585,
+0x3feea09e667f3bcd, 0x3fee9f75e8ec5f74, 0x3feea11473eb0187, 0x3feea589994cce13,
+0x3feeace5422aa0db, 0x3feeb737b0cdc5e5, 0x3feec49182a3f090, 0x3feed503b23e255d,
+0x3feee89f995ad3ad, 0x3feeff76f2fb5e47, 0x3fef199bdd85529c, 0x3fef3720dcef9069,
+0x3fef5818dcfba487, 0x3fef7c97337b9b5f, 0x3fefa4afa2a490da, 0x3fefd0765b6e4540,
+ },
+ .shift_scaled = 0x1.8p+52 / N,
+ .poly = {
+ 0x1.c6af84b912394p-5, 0x1.ebfce50fac4f3p-3, 0x1.62e42ff0c52d6p-1,
+ },
+ .shift = 0x1.8p+52,
+ .invln2_scaled = 0x1.71547652b82fep+0 * N,
+ .poly_scaled = {
+ 0x1.c6af84b912394p-5/N/N/N, 0x1.ebfce50fac4f3p-3/N/N, 0x1.62e42ff0c52d6p-1/N,
+ },
+};
--- /dev/null
+/*
+ * Copyright (c) 2017-2018, Arm Limited.
+ * SPDX-License-Identifier: MIT
+ */
+#ifndef _EXP2F_DATA_H
+#define _EXP2F_DATA_H
+
+#include <features.h>
+#include <stdint.h>
+
+/* Shared between expf, exp2f and powf. */
+#define EXP2F_TABLE_BITS 5
+#define EXP2F_POLY_ORDER 3
+extern hidden const struct exp2f_data {
+ uint64_t tab[1 << EXP2F_TABLE_BITS];
+ double shift_scaled;
+ double poly[EXP2F_POLY_ORDER];
+ double shift;
+ double invln2_scaled;
+ double poly_scaled[EXP2F_POLY_ORDER];
+} __exp2f_data;
+
+#endif
-/* origin: FreeBSD /usr/src/lib/msun/src/e_expf.c */
/*
- * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
- */
-/*
- * ====================================================
- * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ * Single-precision e^x function.
*
- * Developed at SunPro, a Sun Microsystems, Inc. business.
- * Permission to use, copy, modify, and distribute this
- * software is freely granted, provided that this notice
- * is preserved.
- * ====================================================
+ * Copyright (c) 2017-2018, Arm Limited.
+ * SPDX-License-Identifier: MIT
*/
+#include <math.h>
+#include <stdint.h>
#include "libm.h"
+#include "exp2f_data.h"
-static const float
-half[2] = {0.5,-0.5},
-ln2hi = 6.9314575195e-1f, /* 0x3f317200 */
-ln2lo = 1.4286067653e-6f, /* 0x35bfbe8e */
-invln2 = 1.4426950216e+0f, /* 0x3fb8aa3b */
/*
- * Domain [-0.34568, 0.34568], range ~[-4.278e-9, 4.447e-9]:
- * |x*(exp(x)+1)/(exp(x)-1) - p(x)| < 2**-27.74
- */
-P1 = 1.6666625440e-1f, /* 0xaaaa8f.0p-26 */
-P2 = -2.7667332906e-3f; /* -0xb55215.0p-32 */
+EXP2F_TABLE_BITS = 5
+EXP2F_POLY_ORDER = 3
-float expf(float x)
+ULP error: 0.502 (nearest rounding.)
+Relative error: 1.69 * 2^-34 in [-ln2/64, ln2/64] (before rounding.)
+Wrong count: 170635 (all nearest rounding wrong results with fma.)
+Non-nearest ULP error: 1 (rounded ULP error)
+*/
+
+#define N (1 << EXP2F_TABLE_BITS)
+#define InvLn2N __exp2f_data.invln2_scaled
+#define T __exp2f_data.tab
+#define C __exp2f_data.poly_scaled
+
+static inline uint32_t top12(float x)
{
- float_t hi, lo, c, xx, y;
- int k, sign;
- uint32_t hx;
+ return asuint(x) >> 20;
+}
- GET_FLOAT_WORD(hx, x);
- sign = hx >> 31; /* sign bit of x */
- hx &= 0x7fffffff; /* high word of |x| */
+float expf(float x)
+{
+ uint32_t abstop;
+ uint64_t ki, t;
+ double_t kd, xd, z, r, r2, y, s;
- /* special cases */
- if (hx >= 0x42aeac50) { /* if |x| >= -87.33655f or NaN */
- if (hx > 0x7f800000) /* NaN */
- return x;
- if (hx >= 0x42b17218 && !sign) { /* x >= 88.722839f */
- /* overflow */
- x *= 0x1p127f;
- return x;
- }
- if (sign) {
- /* underflow */
- FORCE_EVAL(-0x1p-149f/x);
- if (hx >= 0x42cff1b5) /* x <= -103.972084f */
- return 0;
- }
+ xd = (double_t)x;
+ abstop = top12(x) & 0x7ff;
+ if (predict_false(abstop >= top12(88.0f))) {
+ /* |x| >= 88 or x is nan. */
+ if (asuint(x) == asuint(-INFINITY))
+ return 0.0f;
+ if (abstop >= top12(INFINITY))
+ return x + x;
+ if (x > 0x1.62e42ep6f) /* x > log(0x1p128) ~= 88.72 */
+ return __math_oflowf(0);
+ if (x < -0x1.9fe368p6f) /* x < log(0x1p-150) ~= -103.97 */
+ return __math_uflowf(0);
}
- /* argument reduction */
- if (hx > 0x3eb17218) { /* if |x| > 0.5 ln2 */
- if (hx > 0x3f851592) /* if |x| > 1.5 ln2 */
- k = invln2*x + half[sign];
- else
- k = 1 - sign - sign;
- hi = x - k*ln2hi; /* k*ln2hi is exact here */
- lo = k*ln2lo;
- x = hi - lo;
- } else if (hx > 0x39000000) { /* |x| > 2**-14 */
- k = 0;
- hi = x;
- lo = 0;
- } else {
- /* raise inexact */
- FORCE_EVAL(0x1p127f + x);
- return 1 + x;
- }
+ /* x*N/Ln2 = k + r with r in [-1/2, 1/2] and int k. */
+ z = InvLn2N * xd;
+
+ /* Round and convert z to int, the result is in [-150*N, 128*N] and
+ ideally ties-to-even rule is used, otherwise the magnitude of r
+ can be bigger which gives larger approximation error. */
+#if TOINT_INTRINSICS
+ kd = roundtoint(z);
+ ki = converttoint(z);
+#else
+# define SHIFT __exp2f_data.shift
+ kd = eval_as_double(z + SHIFT);
+ ki = asuint64(kd);
+ kd -= SHIFT;
+#endif
+ r = z - kd;
- /* x is now in primary range */
- xx = x*x;
- c = x - xx*(P1+xx*P2);
- y = 1 + (x*c/(2-c) - lo + hi);
- if (k == 0)
- return y;
- return scalbnf(y, k);
+ /* exp(x) = 2^(k/N) * 2^(r/N) ~= s * (C0*r^3 + C1*r^2 + C2*r + 1) */
+ t = T[ki % N];
+ t += ki << (52 - EXP2F_TABLE_BITS);
+ s = asdouble(t);
+ z = C[0] * r + C[1];
+ r2 = r * r;
+ y = C[2] * r + 1;
+ y = z * r2 + y;
+ y = y * s;
+ return eval_as_float(y);
}
projects / oweals / musl.git / commitdiff