| 1 | /* Round to nearest integer value, rounding halfway cases to even. |
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| 2 | Copyright (C) 2016-2022 Free Software Foundation, Inc. |
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| 3 | This file is part of the GNU C Library. |
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| 4 | |
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| 5 | The GNU C Library is free software; you can redistribute it and/or |
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| 6 | modify it under the terms of the GNU Lesser General Public |
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| 7 | License as published by the Free Software Foundation; either |
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| 8 | version 2.1 of the License, or (at your option) any later version. |
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| 9 | |
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| 10 | The GNU C Library is distributed in the hope that it will be useful, |
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| 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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| 12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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| 13 | Lesser General Public License for more details. |
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| 14 | |
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| 15 | You should have received a copy of the GNU Lesser General Public |
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| 16 | License along with the GNU C Library; if not, see |
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| 17 | <https://www.gnu.org/licenses/>. */ |
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| 18 | |
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| 19 | #define NO_MATH_REDIRECT |
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| 20 | #include <math.h> |
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| 21 | #include <math_private.h> |
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| 22 | #include <libm-alias-double.h> |
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| 23 | #include <stdint.h> |
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| 24 | #include <math-use-builtins.h> |
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| 25 | |
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| 26 | #define BIAS 0x3ff |
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| 27 | #define MANT_DIG 53 |
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| 28 | #define MAX_EXP (2 * BIAS + 1) |
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| 29 | |
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| 30 | double |
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| 31 | __roundeven (double x) |
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| 32 | { |
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| 33 | #if USE_ROUNDEVEN_BUILTIN |
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| 34 | return __builtin_roundeven (x); |
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| 35 | #else |
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| 36 | uint64_t ix, ux; |
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| 37 | EXTRACT_WORDS64 (ix, x); |
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| 38 | ux = ix & 0x7fffffffffffffffULL; |
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| 39 | int exponent = ux >> (MANT_DIG - 1); |
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| 40 | if (exponent >= BIAS + MANT_DIG - 1) |
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| 41 | { |
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| 42 | /* Integer, infinity or NaN. */ |
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| 43 | if (exponent == MAX_EXP) |
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| 44 | /* Infinity or NaN; quiet signaling NaNs. */ |
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| 45 | return x + x; |
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| 46 | else |
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| 47 | return x; |
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| 48 | } |
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| 49 | else if (exponent >= BIAS) |
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| 50 | { |
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| 51 | /* At least 1; not necessarily an integer. Locate the bits with |
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| 52 | exponents 0 and -1 (when the unbiased exponent is 0, the bit |
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| 53 | with exponent 0 is implicit, but as the bias is odd it is OK |
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| 54 | to take it from the low bit of the exponent). */ |
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| 55 | int int_pos = (BIAS + MANT_DIG - 1) - exponent; |
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| 56 | int half_pos = int_pos - 1; |
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| 57 | uint64_t half_bit = 1ULL << half_pos; |
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| 58 | uint64_t int_bit = 1ULL << int_pos; |
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| 59 | if ((ix & (int_bit | (half_bit - 1))) != 0) |
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| 60 | /* Carry into the exponent works correctly. No need to test |
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| 61 | whether HALF_BIT is set. */ |
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| 62 | ix += half_bit; |
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| 63 | ix &= ~(int_bit - 1); |
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| 64 | } |
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| 65 | else if (exponent == BIAS - 1 && ux > 0x3fe0000000000000ULL) |
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| 66 | /* Interval (0.5, 1). */ |
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| 67 | ix = (ix & 0x8000000000000000ULL) | 0x3ff0000000000000ULL; |
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| 68 | else |
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| 69 | /* Rounds to 0. */ |
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| 70 | ix &= 0x8000000000000000ULL; |
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| 71 | INSERT_WORDS64 (x, ix); |
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| 72 | return x; |
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| 73 | #endif /* ! USE_ROUNDEVEN_BUILTIN */ |
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| 74 | } |
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| 75 | #ifndef __roundeven |
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| 76 | libm_alias_double (__roundeven, roundeven) |
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| 77 | #endif |
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| 78 | |
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