src/util/rounding.h

   1 /*
   2  * Copyright © 2015 Intel Corporation
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   8  * and/or sell copies of the Software, and to permit persons to whom the
   9  * Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice (including the next
  12  * paragraph) shall be included in all copies or substantial portions of the
  13  * Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  20  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  21  * IN THE SOFTWARE.
  22  */
  23
  24 #include <math.h>
  25
  26 #ifdef __SSE4_1__
  27 #include <smmintrin.h>
  28 #endif
  29
  30 /* The C standard library has functions round()/rint()/nearbyint() that round
  31  * their arguments according to the rounding mode set in the floating-point
  32  * control register. While there are trunc()/ceil()/floor() functions that do
  33  * a specific operation without modifying the rounding mode, there is no
  34  * roundeven() in any version of C.
  35  *
  36  * Technical Specification 18661 (ISO/IEC TS 18661-1:2014) adds roundeven(),
  37  * but it's unfortunately not implemented by glibc.
  38  *
  39  * This implementation differs in that it does not raise the inexact exception.
  40  *
  41  * We use rint() to implement these functions, with the assumption that the
  42  * floating-point rounding mode has not been changed from the default Round
  43  * to Nearest.
  44  */
  45
  46 /**
  47  * \brief Rounds \c x to the nearest integer, with ties to the even integer.
  48  */
  49 static inline float
  50 _mesa_roundevenf(float x)
  51 {
  52 #ifdef __SSE4_1__
  53    float ret;
  54    __m128 m = _mm_load_ss(&x);
  55    m = _mm_round_ss(m, m, _MM_FROUND_CUR_DIRECTION | _MM_FROUND_NO_EXC);
  56    _mm_store_ss(&ret, m);
  57    return ret;
  58 #else
  59    return rintf(x);
  60 #endif
  61 }
  62
  63 /**
  64  * \brief Rounds \c x to the nearest integer, with ties to the even integer.
  65  */
  66 static inline double
  67 _mesa_roundeven(double x)
  68 {
  69 #ifdef __SSE4_1__
  70    double ret;
  71    __m128d m = _mm_load_sd(&x);
  72    m = _mm_round_sd(m, m, _MM_FROUND_CUR_DIRECTION | _MM_FROUND_NO_EXC);
  73    _mm_store_sd(&ret, m);
  74    return ret;
  75 #else
  76    return rint(x);
  77 #endif
  78 }