diff options
Diffstat (limited to 'sysdeps/ieee754/dbl-64/wordsize-64/s_roundeven.c')
| -rw-r--r-- | sysdeps/ieee754/dbl-64/wordsize-64/s_roundeven.c | 71 |
1 files changed, 71 insertions, 0 deletions
diff --git a/sysdeps/ieee754/dbl-64/wordsize-64/s_roundeven.c b/sysdeps/ieee754/dbl-64/wordsize-64/s_roundeven.c new file mode 100644 index 0000000000..7bbbb2dc20 --- /dev/null +++ b/sysdeps/ieee754/dbl-64/wordsize-64/s_roundeven.c @@ -0,0 +1,71 @@ +/* Round to nearest integer value, rounding halfway cases to even. + dbl-64/wordsize-64 version. + Copyright (C) 2016-2018 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 + <http://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) |