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/* Round to nearest integer value, rounding halfway cases to even.
Copyright (C) 2016-2021 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <math.h>
#include <math_private.h>
#include <libm-alias-double.h>
#include <stdint.h>
#define BIAS 0x3ff
#define MANT_DIG 53
#define MAX_EXP (2 * BIAS + 1)
double
__roundeven (double x)
{
uint64_t ix, ux;
EXTRACT_WORDS64 (ix, x);
ux = ix & 0x7fffffffffffffffULL;
int exponent = ux >> (MANT_DIG - 1);
if (exponent >= BIAS + MANT_DIG - 1)
{
/* Integer, infinity or NaN. */
if (exponent == MAX_EXP)
/* Infinity or NaN; quiet signaling NaNs. */
return x + x;
else
return x;
}
else if (exponent >= BIAS)
{
/* At least 1; not necessarily an integer. Locate the bits with
exponents 0 and -1 (when the unbiased exponent is 0, the bit
with exponent 0 is implicit, but as the bias is odd it is OK
to take it from the low bit of the exponent). */
int int_pos = (BIAS + MANT_DIG - 1) - exponent;
int half_pos = int_pos - 1;
uint64_t half_bit = 1ULL << half_pos;
uint64_t int_bit = 1ULL << int_pos;
if ((ix & (int_bit | (half_bit - 1))) != 0)
/* Carry into the exponent works correctly. No need to test
whether HALF_BIT is set. */
ix += half_bit;
ix &= ~(int_bit - 1);
}
else if (exponent == BIAS - 1 && ux > 0x3fe0000000000000ULL)
/* Interval (0.5, 1). */
ix = (ix & 0x8000000000000000ULL) | 0x3ff0000000000000ULL;
else
/* Rounds to 0. */
ix &= 0x8000000000000000ULL;
INSERT_WORDS64 (x, ix);
return x;
}
hidden_def (__roundeven)
libm_alias_double (__roundeven, roundeven)
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