diff options
Diffstat (limited to 'sysdeps/ieee754/dbl-64/s_roundeven.c')
| -rw-r--r-- | sysdeps/ieee754/dbl-64/s_roundeven.c | 106 |
1 files changed, 106 insertions, 0 deletions
diff --git a/sysdeps/ieee754/dbl-64/s_roundeven.c b/sysdeps/ieee754/dbl-64/s_roundeven.c new file mode 100644 index 0000000000..27e15e35ad --- /dev/null +++ b/sysdeps/ieee754/dbl-64/s_roundeven.c @@ -0,0 +1,106 @@ +/* Round to nearest integer value, rounding halfway cases to even. + dbl-64 version. + Copyright (C) 2016 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 <stdint.h> + +#define BIAS 0x3ff +#define MANT_DIG 53 +#define MAX_EXP (2 * BIAS + 1) + +double +roundeven (double x) +{ + uint32_t hx, lx, uhx; + EXTRACT_WORDS (hx, lx, x); + uhx = hx & 0x7fffffff; + int exponent = uhx >> (MANT_DIG - 1 - 32); + 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 + MANT_DIG - 32) + { + /* Not necessarily an integer; integer bit is in low word. + Locate the bits with exponents 0 and -1. */ + int int_pos = (BIAS + MANT_DIG - 1) - exponent; + int half_pos = int_pos - 1; + uint32_t half_bit = 1U << half_pos; + uint32_t int_bit = 1U << int_pos; + if ((lx & (int_bit | (half_bit - 1))) != 0) + { + /* Carry into the exponent works correctly. No need to test + whether HALF_BIT is set. */ + lx += half_bit; + hx += lx < half_bit; + } + lx &= ~(int_bit - 1); + } + else if (exponent == BIAS + MANT_DIG - 33) + { + /* Not necessarily an integer; integer bit is bottom of high + word, half bit is top of low word. */ + if (((hx & 1) | (lx & 0x7fffffff)) != 0) + { + lx += 0x80000000; + hx += lx < 0x80000000; + } + lx = 0; + } + else if (exponent >= BIAS) + { + /* At least 1; not necessarily an integer, integer bit and half + bit are in the high word. 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 - 33) - exponent; + int half_pos = int_pos - 1; + uint32_t half_bit = 1U << half_pos; + uint32_t int_bit = 1U << int_pos; + if (((hx & (int_bit | (half_bit - 1))) | lx) != 0) + hx += half_bit; + hx &= ~(int_bit - 1); + lx = 0; + } + else if (exponent == BIAS - 1 && (uhx > 0x3fe00000 || lx != 0)) + { + /* Interval (0.5, 1). */ + hx = (hx & 0x80000000) | 0x3ff00000; + lx = 0; + } + else + { + /* Rounds to 0. */ + hx &= 0x80000000; + lx = 0; + } + INSERT_WORDS (x, hx, lx); + return x; +} +hidden_def (roundeven) +#ifdef NO_LONG_DOUBLE +weak_alias (roundeven, roundevenl) +#endif |