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125 lines
3.1 KiB
C
125 lines
3.1 KiB
C
/* Round to nearest integer value, rounding halfway cases to even.
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ldbl-96 version.
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Copyright (C) 2016-2017 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <math.h>
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#include <math_private.h>
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#include <stdint.h>
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#define BIAS 0x3fff
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#define MANT_DIG 64
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#define MAX_EXP (2 * BIAS + 1)
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long double
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roundevenl (long double x)
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{
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uint16_t se;
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uint32_t hx, lx;
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GET_LDOUBLE_WORDS (se, hx, lx, x);
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int exponent = se & 0x7fff;
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if (exponent >= BIAS + MANT_DIG - 1)
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{
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/* Integer, infinity or NaN. */
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if (exponent == MAX_EXP)
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/* Infinity or NaN; quiet signaling NaNs. */
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return x + x;
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else
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return x;
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}
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else if (exponent >= BIAS + MANT_DIG - 32)
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{
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/* Not necessarily an integer; integer bit is in low word.
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Locate the bits with exponents 0 and -1. */
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int int_pos = (BIAS + MANT_DIG - 1) - exponent;
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int half_pos = int_pos - 1;
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uint32_t half_bit = 1U << half_pos;
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uint32_t int_bit = 1U << int_pos;
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if ((lx & (int_bit | (half_bit - 1))) != 0)
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{
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/* No need to test whether HALF_BIT is set. */
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lx += half_bit;
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if (lx < half_bit)
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{
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hx++;
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if (hx == 0)
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{
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hx = 0x80000000;
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se++;
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}
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}
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}
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lx &= ~(int_bit - 1);
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}
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else if (exponent == BIAS + MANT_DIG - 33)
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{
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/* Not necessarily an integer; integer bit is bottom of high
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word, half bit is top of low word. */
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if (((hx & 1) | (lx & 0x7fffffff)) != 0)
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{
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lx += 0x80000000;
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if (lx < 0x80000000)
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{
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hx++;
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if (hx == 0)
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{
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hx = 0x80000000;
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se++;
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}
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}
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}
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lx = 0;
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}
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else if (exponent >= BIAS)
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{
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/* At least 1; not necessarily an integer, integer bit and half
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bit are in the high word. Locate the bits with exponents 0
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and -1. */
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int int_pos = (BIAS + MANT_DIG - 33) - exponent;
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int half_pos = int_pos - 1;
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uint32_t half_bit = 1U << half_pos;
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uint32_t int_bit = 1U << int_pos;
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if (((hx & (int_bit | (half_bit - 1))) | lx) != 0)
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{
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hx += half_bit;
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if (hx < half_bit)
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{
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hx = 0x80000000;
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se++;
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}
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}
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hx &= ~(int_bit - 1);
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lx = 0;
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}
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else if (exponent == BIAS - 1 && (hx > 0x80000000 || lx != 0))
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{
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/* Interval (0.5, 1). */
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se = (se & 0x8000) | 0x3fff;
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hx = 0x80000000;
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lx = 0;
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}
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else
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{
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/* Rounds to 0. */
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se &= 0x8000;
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hx = 0;
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lx = 0;
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}
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SET_LDOUBLE_WORDS (x, se, hx, lx);
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return x;
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}
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