xapian-core/common/min_non_zero.h

   1 /** @file
   2  * @brief Return the smaller of two numbers which isn't zero.
   3  */
   4 /* Copyright (C) 2018 Olly Betts
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a copy
   7  * of this software and associated documentation files (the "Software"), to
   8  * deal in the Software without restriction, including without limitation the
   9  * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
  10  * sell copies of the Software, and to permit persons to whom the Software is
  11  * furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included in
  14  * all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  19  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  21  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  22  * IN THE SOFTWARE.
  23  */
  24
  25 #ifndef XAPIAN_INCLUDED_MIN_NON_ZERO_H
  26 #define XAPIAN_INCLUDED_MIN_NON_ZERO_H
  27
  28 #include <algorithm>
  29
  30 /** Return the smaller of two unsigned integers which isn't zero.
  31  *
  32  *  If both a and b are zero, returns zero.
  33  */
  34 template<typename T>
  35 constexpr typename std::enable_if<std::is_unsigned<T>::value, T>::type
  36 min_non_zero(const T& a, const T& b)
  37 {
  38     // To achieve the effect we want, we find the *maximum* after negating each
  39     // of the values (which for an unsigned type leaves 0 alone but flips the
  40     // order of all other values), then negate the answer.
  41     return -std::max(-a, -b);
  42 }
  43
  44 #endif // XAPIAN_INCLUDED_MIN_NON_ZERO_H