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475 lines
12 KiB
C
475 lines
12 KiB
C
/* Copyright 2016 Samsung Electronics Co., Ltd.
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* Copyright 2016 University of Szeged
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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* This file is based on work under the following copyright and permission
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* notice:
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*
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* Copyright (C) 2004 by Sun Microsystems, Inc. All rights reserved.
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*
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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*
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* @(#)e_pow.c 1.5 04/04/22
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*/
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#include "jerry-libm-internal.h"
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/* pow(x,y) return x**y
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*
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* n
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* Method: Let x = 2 * (1+f)
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* 1. Compute and return log2(x) in two pieces:
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* log2(x) = w1 + w2,
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* where w1 has 53-24 = 29 bit trailing zeros.
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* 2. Perform y*log2(x) = n+y' by simulating muti-precision
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* arithmetic, where |y'|<=0.5.
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* 3. Return x**y = 2**n*exp(y'*log2)
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*
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* Special cases:
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* 0. +1 ** (anything) is 1
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* 1. (anything) ** 0 is 1
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* 2. (anything) ** 1 is itself
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* 3. (anything) ** NAN is NAN
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* 4. NAN ** (anything except 0) is NAN
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* 5. +-(|x| > 1) ** +INF is +INF
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* 6. +-(|x| > 1) ** -INF is +0
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* 7. +-(|x| < 1) ** +INF is +0
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* 8. +-(|x| < 1) ** -INF is +INF
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* 9. -1 ** +-INF is 1
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* 10. +0 ** (+anything except 0, NAN) is +0
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* 11. -0 ** (+anything except 0, NAN, odd integer) is +0
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* 12. +0 ** (-anything except 0, NAN) is +INF
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* 13. -0 ** (-anything except 0, NAN, odd integer) is +INF
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* 14. -0 ** (odd integer) = -( +0 ** (odd integer) )
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* 15. +INF ** (+anything except 0,NAN) is +INF
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* 16. +INF ** (-anything except 0,NAN) is +0
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* 17. -INF ** (anything) = -0 ** (-anything)
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* 18. (-anything) ** (integer) is (-1)**(integer)*(+anything**integer)
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* 19. (-anything except 0 and inf) ** (non-integer) is NAN
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*
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* Accuracy:
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* pow(x,y) returns x**y nearly rounded. In particular
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* pow(integer,integer)
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* always returns the correct integer provided it is
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* representable.
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*
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* Constants:
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* The hexadecimal values are the intended ones for the following
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* constants. The decimal values may be used, provided that the
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* compiler will convert from decimal to binary accurately enough
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* to produce the hexadecimal values shown.
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*/
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static const double bp[] =
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{
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1.0,
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1.5,
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};
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static const double dp_h[] =
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{
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0.0,
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5.84962487220764160156e-01, /* 0x3FE2B803, 0x40000000 */
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};
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static const double dp_l[] =
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{
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0.0,
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1.35003920212974897128e-08, /* 0x3E4CFDEB, 0x43CFD006 */
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};
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#define zero 0.0
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#define one 1.0
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#define two 2.0
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#define two53 9007199254740992.0 /* 0x43400000, 0x00000000 */
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#define huge 1.0e300
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#define tiny 1.0e-300
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/* poly coefs for (3/2) * (log(x) - 2s - 2/3 * s**3 */
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#define L1 5.99999999999994648725e-01 /* 0x3FE33333, 0x33333303 */
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#define L2 4.28571428578550184252e-01 /* 0x3FDB6DB6, 0xDB6FABFF */
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#define L3 3.33333329818377432918e-01 /* 0x3FD55555, 0x518F264D */
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#define L4 2.72728123808534006489e-01 /* 0x3FD17460, 0xA91D4101 */
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#define L5 2.30660745775561754067e-01 /* 0x3FCD864A, 0x93C9DB65 */
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#define L6 2.06975017800338417784e-01 /* 0x3FCA7E28, 0x4A454EEF */
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#define P1 1.66666666666666019037e-01 /* 0x3FC55555, 0x5555553E */
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#define P2 -2.77777777770155933842e-03 /* 0xBF66C16C, 0x16BEBD93 */
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#define P3 6.61375632143793436117e-05 /* 0x3F11566A, 0xAF25DE2C */
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#define P4 -1.65339022054652515390e-06 /* 0xBEBBBD41, 0xC5D26BF1 */
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#define P5 4.13813679705723846039e-08 /* 0x3E663769, 0x72BEA4D0 */
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#define lg2 6.93147180559945286227e-01 /* 0x3FE62E42, 0xFEFA39EF */
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#define lg2_h 6.93147182464599609375e-01 /* 0x3FE62E43, 0x00000000 */
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#define lg2_l -1.90465429995776804525e-09 /* 0xBE205C61, 0x0CA86C39 */
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#define ovt 8.0085662595372944372e-0017 /* -(1024-log2(ovfl+.5ulp)) */
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#define cp 9.61796693925975554329e-01 /* 0x3FEEC709, 0xDC3A03FD = 2 / (3 ln2) */
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#define cp_h 9.61796700954437255859e-01 /* 0x3FEEC709, 0xE0000000 = (float) cp */
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#define cp_l -7.02846165095275826516e-09 /* 0xBE3E2FE0, 0x145B01F5 = tail of cp_h */
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#define ivln2 1.44269504088896338700e+00 /* 0x3FF71547, 0x652B82FE = 1 / ln2 */
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#define ivln2_h 1.44269502162933349609e+00 /* 0x3FF71547, 0x60000000 = 24b 1 / ln2 */
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#define ivln2_l 1.92596299112661746887e-08 /* 0x3E54AE0B, 0xF85DDF44 = 1 / ln2 tail */
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double
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pow (double x, double y)
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{
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double z, ax, z_h, z_l, p_h, p_l;
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double y1, t1, t2, r, s, t, u, v, w;
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int i, j, k, yisint, n;
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int hx, hy, ix, iy;
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unsigned lx, ly;
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hx = __HI (x);
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lx = __LO (x);
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hy = __HI (y);
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ly = __LO (y);
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ix = hx & 0x7fffffff;
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iy = hy & 0x7fffffff;
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/* x == one: 1**y = 1 */
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if (((hx - 0x3ff00000) | lx) == 0)
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{
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return one;
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}
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/* y == zero: x**0 = 1 */
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if ((iy | ly) == 0)
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{
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return one;
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}
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/* +-NaN return x + y */
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if (ix > 0x7ff00000 || ((ix == 0x7ff00000) && (lx != 0)) || iy > 0x7ff00000 || ((iy == 0x7ff00000) && (ly != 0)))
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{
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return x + y;
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}
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/* determine if y is an odd int when x < 0
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* yisint = 0 ... y is not an integer
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* yisint = 1 ... y is an odd int
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* yisint = 2 ... y is an even int
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*/
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yisint = 0;
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if (hx < 0)
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{
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if (iy >= 0x43400000) /* even integer y */
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{
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yisint = 2;
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}
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else if (iy >= 0x3ff00000)
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{
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k = (iy >> 20) - 0x3ff; /* exponent */
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if (k > 20)
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{
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j = ly >> (52 - k);
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if ((j << (52 - k)) == ly)
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{
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yisint = 2 - (j & 1);
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}
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}
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else if (ly == 0)
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{
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j = iy >> (20 - k);
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if ((j << (20 - k)) == iy)
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{
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yisint = 2 - (j & 1);
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}
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}
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}
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}
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/* special value of y */
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if (ly == 0)
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{
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if (iy == 0x7ff00000) /* y is +-inf */
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{
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if (((ix - 0x3ff00000) | lx) == 0) /* +-1**+-inf is 1 */
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{
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return one;
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}
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else if (ix >= 0x3ff00000) /* (|x|>1)**+-inf = inf,0 */
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{
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return (hy >= 0) ? y : zero;
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}
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else /* (|x|<1)**-,+inf = inf,0 */
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{
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return (hy < 0) ? -y : zero;
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}
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}
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if (iy == 0x3ff00000) /* y is +-1 */
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{
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if (hy < 0)
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{
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return one / x;
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}
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else
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{
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return x;
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}
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}
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if (hy == 0x40000000) /* y is 2 */
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{
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return x * x;
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}
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if (hy == 0x3fe00000) /* y is 0.5 */
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{
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if (hx >= 0) /* x >= +0 */
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{
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return sqrt (x);
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}
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}
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}
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ax = fabs (x);
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/* special value of x */
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if (lx == 0)
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{
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if (ix == 0x7ff00000 || ix == 0 || ix == 0x3ff00000)
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{
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z = ax; /* x is +-0,+-inf,+-1 */
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if (hy < 0)
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{
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z = one / z; /* z = (1 / |x|) */
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}
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if (hx < 0)
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{
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if (((ix - 0x3ff00000) | yisint) == 0)
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{
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z = (z - z) / (z - z); /* (-1)**non-int is NaN */
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}
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else if (yisint == 1)
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{
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z = -z; /* (x<0)**odd = -(|x|**odd) */
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}
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}
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return z;
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}
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}
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n = (hx >> 31) + 1;
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/* (x<0)**(non-int) is NaN */
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if ((n | yisint) == 0)
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{
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return (x - x) / (x - x);
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}
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s = one; /* s (sign of result -ve**odd) = -1 else = 1 */
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if ((n | (yisint - 1)) == 0)
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{
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s = -one; /* (-ve)**(odd int) */
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}
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/* |y| is huge */
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if (iy > 0x41e00000) /* if |y| > 2**31 */
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{
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if (iy > 0x43f00000) /* if |y| > 2**64, must o/uflow */
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{
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if (ix <= 0x3fefffff)
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{
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return (hy < 0) ? huge * huge : tiny * tiny;
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}
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if (ix >= 0x3ff00000)
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{
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return (hy > 0) ? huge * huge : tiny * tiny;
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}
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}
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/* over/underflow if x is not close to one */
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if (ix < 0x3fefffff)
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{
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return (hy < 0) ? s * huge * huge : s * tiny * tiny;
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}
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if (ix > 0x3ff00000)
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{
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return (hy > 0) ? s * huge * huge : s * tiny * tiny;
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}
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/* now |1 - x| is tiny <= 2**-20, suffice to compute
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log(x) by x - x^2 / 2 + x^3 / 3 - x^4 / 4 */
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t = ax - one; /* t has 20 trailing zeros */
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w = (t * t) * (0.5 - t * (0.3333333333333333333333 - t * 0.25));
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u = ivln2_h * t; /* ivln2_h has 21 sig. bits */
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v = t * ivln2_l - w * ivln2;
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t1 = u + v;
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__LO (t1) = 0;
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t2 = v - (t1 - u);
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}
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else
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{
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double ss, s2, s_h, s_l, t_h, t_l;
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n = 0;
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/* take care subnormal number */
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if (ix < 0x00100000)
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{
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ax *= two53;
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n -= 53;
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ix = __HI (ax);
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}
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n += ((ix) >> 20) - 0x3ff;
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j = ix & 0x000fffff;
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/* determine interval */
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ix = j | 0x3ff00000; /* normalize ix */
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if (j <= 0x3988E) /* |x| < sqrt(3/2) */
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{
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k = 0;
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}
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else if (j < 0xBB67A) /* |x| < sqrt(3) */
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{
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k = 1;
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}
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else
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{
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k = 0;
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n += 1;
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ix -= 0x00100000;
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}
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__HI (ax) = ix;
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/* compute ss = s_h + s_l = (x - 1) / (x + 1) or (x - 1.5) / (x + 1.5) */
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u = ax - bp[k]; /* bp[0] = 1.0, bp[1] = 1.5 */
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v = one / (ax + bp[k]);
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ss = u * v;
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s_h = ss;
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__LO (s_h) = 0;
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/* t_h = ax + bp[k] High */
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t_h = zero;
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__HI (t_h) = ((ix >> 1) | 0x20000000) + 0x00080000 + (k << 18);
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t_l = ax - (t_h - bp[k]);
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s_l = v * ((u - s_h * t_h) - s_h * t_l);
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/* compute log(ax) */
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s2 = ss * ss;
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r = s2 * s2 * (L1 + s2 * (L2 + s2 * (L3 + s2 * (L4 + s2 * (L5 + s2 * L6)))));
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r += s_l * (s_h + ss);
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s2 = s_h * s_h;
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t_h = 3.0 + s2 + r;
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__LO (t_h) = 0;
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t_l = r - ((t_h - 3.0) - s2);
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/* u + v = ss * (1 + ...) */
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u = s_h * t_h;
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v = s_l * t_h + t_l * ss;
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/* 2 / (3 * log2) * (ss + ...) */
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p_h = u + v;
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__LO (p_h) = 0;
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p_l = v - (p_h - u);
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z_h = cp_h * p_h; /* cp_h + cp_l = 2 / (3 * log2) */
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z_l = cp_l * p_h + p_l * cp + dp_l[k];
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/* log2(ax) = (ss + ...) * 2 / (3 * log2) = n + dp_h + z_h + z_l */
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t = (double) n;
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t1 = (((z_h + z_l) + dp_h[k]) + t);
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__LO (t1) = 0;
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t2 = z_l - (((t1 - t) - dp_h[k]) - z_h);
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}
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/* split up y into y1 + y2 and compute (y1 + y2) * (t1 + t2) */
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y1 = y;
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__LO (y1) = 0;
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p_l = (y - y1) * t1 + y * t2;
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p_h = y1 * t1;
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z = p_l + p_h;
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j = __HI (z);
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i = __LO (z);
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if (j >= 0x40900000) /* z >= 1024 */
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{
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if (((j - 0x40900000) | i) != 0) /* if z > 1024 */
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{
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return s * huge * huge; /* overflow */
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}
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else
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{
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if (p_l + ovt > z - p_h)
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{
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return s * huge * huge; /* overflow */
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}
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}
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}
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else if ((j & 0x7fffffff) >= 0x4090cc00) /* z <= -1075 */
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{
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if (((j - 0xc090cc00) | i) != 0) /* z < -1075 */
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{
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return s * tiny * tiny; /* underflow */
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}
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else
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{
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if (p_l <= z - p_h)
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{
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return s * tiny * tiny; /* underflow */
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}
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}
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}
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/*
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* compute 2**(p_h + p_l)
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*/
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i = j & 0x7fffffff;
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k = (i >> 20) - 0x3ff;
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n = 0;
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if (i > 0x3fe00000) /* if |z| > 0.5, set n = [z + 0.5] */
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{
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n = j + (0x00100000 >> (k + 1));
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k = ((n & 0x7fffffff) >> 20) - 0x3ff; /* new k for n */
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t = zero;
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__HI (t) = (n & ~(0x000fffff >> k));
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n = ((n & 0x000fffff) | 0x00100000) >> (20 - k);
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if (j < 0)
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{
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n = -n;
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}
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p_h -= t;
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}
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t = p_l + p_h;
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__LO (t) = 0;
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u = t * lg2_h;
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v = (p_l - (t - p_h)) * lg2 + t * lg2_l;
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z = u + v;
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w = v - (z - u);
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t = z * z;
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t1 = z - t * (P1 + t * (P2 + t * (P3 + t * (P4 + t * P5))));
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r = (z * t1) / (t1 - two) - (w + z * w);
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z = one - (r - z);
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j = __HI (z);
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j += (n << 20);
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if ((j >> 20) <= 0) /* subnormal output */
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{
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z = scalbn (z, n);
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}
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else
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{
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__HI (z) += (n << 20);
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}
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return s * z;
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} /* pow */
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#undef zero
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#undef one
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#undef two
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#undef two53
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#undef huge
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#undef tiny
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#undef L1
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#undef L2
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#undef L3
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#undef L4
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#undef L5
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#undef L6
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#undef P1
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#undef P2
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#undef P3
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|
#undef P4
|
|
#undef P5
|
|
#undef lg2
|
|
#undef lg2_h
|
|
#undef lg2_l
|
|
#undef ovt
|
|
#undef cp
|
|
#undef cp_h
|
|
#undef cp_l
|
|
#undef ivln2
|
|
#undef ivln2_h
|
|
#undef ivln2_l
|