78 lines
2.5 KiB
C
78 lines
2.5 KiB
C
/* Round to nearest integer value, rounding halfway cases to even.
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Copyright (C) 2016-2022 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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<https://www.gnu.org/licenses/>. */
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#define NO_MATH_REDIRECT
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#include <math.h>
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#include <math_private.h>
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#include <libm-alias-double.h>
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#include <stdint.h>
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#include <math-use-builtins.h>
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#define BIAS 0x3ff
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#define MANT_DIG 53
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#define MAX_EXP (2 * BIAS + 1)
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double
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__roundeven (double x)
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{
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#if USE_ROUNDEVEN_BUILTIN
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return __builtin_roundeven (x);
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#else
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uint64_t ix, ux;
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EXTRACT_WORDS64 (ix, x);
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ux = ix & 0x7fffffffffffffffULL;
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int exponent = ux >> (MANT_DIG - 1);
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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)
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{
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/* At least 1; not necessarily an integer. Locate the bits with
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exponents 0 and -1 (when the unbiased exponent is 0, the bit
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with exponent 0 is implicit, but as the bias is odd it is OK
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to take it from the low bit of the exponent). */
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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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uint64_t half_bit = 1ULL << half_pos;
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uint64_t int_bit = 1ULL << int_pos;
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if ((ix & (int_bit | (half_bit - 1))) != 0)
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/* Carry into the exponent works correctly. No need to test
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whether HALF_BIT is set. */
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ix += half_bit;
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ix &= ~(int_bit - 1);
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}
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else if (exponent == BIAS - 1 && ux > 0x3fe0000000000000ULL)
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/* Interval (0.5, 1). */
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ix = (ix & 0x8000000000000000ULL) | 0x3ff0000000000000ULL;
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else
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/* Rounds to 0. */
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ix &= 0x8000000000000000ULL;
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INSERT_WORDS64 (x, ix);
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return x;
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#endif /* ! USE_ROUNDEVEN_BUILTIN */
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}
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#ifndef __roundeven
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libm_alias_double (__roundeven, roundeven)
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#endif
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