src/util/rounding.h

/*
 * Copyright © 2015 Intel Corporation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#include <math.h>

#ifdef __SSE4_1__
#include <smmintrin.h>
#endif

/* The C standard library has functions round()/rint()/nearbyint() that round
 * their arguments according to the rounding mode set in the floating-point
 * control register. While there are trunc()/ceil()/floor() functions that do
 * a specific operation without modifying the rounding mode, there is no
 * roundeven() in any version of C.
 *
 * Technical Specification 18661 (ISO/IEC TS 18661-1:2014) adds roundeven(),
 * but it's unfortunately not implemented by glibc.
 *
 * This implementation differs in that it does not raise the inexact exception.
 *
 * We use rint() to implement these functions, with the assumption that the
 * floating-point rounding mode has not been changed from the default Round
 * to Nearest.
 */

/**
 * \brief Rounds \c x to the nearest integer, with ties to the even integer.
 */
static inline float
_mesa_roundevenf(float x)
{
#ifdef __SSE4_1__
   float ret;
   __m128 m = _mm_load_ss(&x);
   m = _mm_round_ss(m, m, _MM_FROUND_CUR_DIRECTION | _MM_FROUND_NO_EXC);
   _mm_store_ss(&ret, m);
   return ret;
#else
   return rintf(x);
#endif
}

/**
 * \brief Rounds \c x to the nearest integer, with ties to the even integer.
 */
static inline double
_mesa_roundeven(double x)
{
#ifdef __SSE4_1__
   double ret;
   __m128d m = _mm_load_sd(&x);
   m = _mm_round_sd(m, m, _MM_FROUND_CUR_DIRECTION | _MM_FROUND_NO_EXC);
   _mm_store_sd(&ret, m);
   return ret;
#else
   return rint(x);
#endif
}