sysdeps/ieee754/flt-32/s_roundevenf.c

   1 /* Round to nearest integer value, rounding halfway cases to even.
   2    flt-32 version.
   3    Copyright (C) 2016-2023 Free Software Foundation, Inc.
   4    This file is part of the GNU C Library.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <https://www.gnu.org/licenses/>.  */
  19
  20 #define NO_MATH_REDIRECT
  21 #include <math.h>
  22 #include <math_private.h>
  23 #include <libm-alias-float.h>
  24 #include <math-use-builtins.h>
  25 #include <stdint.h>
  26
  27 #define BIAS 0x7f
  28 #define MANT_DIG 24
  29 #define MAX_EXP (2 * BIAS + 1)
  30
  31 float
  32 __roundevenf (float x)
  33 {
  34 #if USE_ROUNDEVENF_BUILTIN
  35   return __builtin_roundevenf (x);
  36 #else
  37   uint32_t ix, ux;
  38   GET_FLOAT_WORD (ix, x);
  39   ux = ix & 0x7fffffff;
  40   int exponent = ux >> (MANT_DIG - 1);
  41   if (exponent >= BIAS + MANT_DIG - 1)
  42     {
  43       /* Integer, infinity or NaN.  */
  44       if (exponent == MAX_EXP)
  45         /* Infinity or NaN; quiet signaling NaNs.  */
  46         return x + x;
  47       else
  48         return x;
  49     }
  50   else if (exponent >= BIAS)
  51     {
  52       /* At least 1; not necessarily an integer.  Locate the bits with
  53          exponents 0 and -1 (when the unbiased exponent is 0, the bit
  54          with exponent 0 is implicit, but as the bias is odd it is OK
  55          to take it from the low bit of the exponent).  */
  56       int int_pos = (BIAS + MANT_DIG - 1) - exponent;
  57       int half_pos = int_pos - 1;
  58       uint32_t half_bit = 1U << half_pos;
  59       uint32_t int_bit = 1U << int_pos;
  60       if ((ix & (int_bit | (half_bit - 1))) != 0)
  61         /* Carry into the exponent works correctly.  No need to test
  62            whether HALF_BIT is set.  */
  63         ix += half_bit;
  64       ix &= ~(int_bit - 1);
  65     }
  66   else if (exponent == BIAS - 1 && ux > 0x3f000000)
  67     /* Interval (0.5, 1).  */
  68     ix = (ix & 0x80000000) | 0x3f800000;
  69   else
  70     /* Rounds to 0.  */
  71     ix &= 0x80000000;
  72   SET_FLOAT_WORD (x, ix);
  73   return x;
  74 #endif /* ! USE_ROUNDEVENF_BUILTIN  */
  75 }
  76 #ifndef __roundevenf
  77 libm_alias_float (__roundeven, roundeven)
  78 #endif