libcxx/include/__numeric/saturation_arithmetic.h

   1 // -*- C++ -*-
   2 //===----------------------------------------------------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #ifndef _LIBCPP___NUMERIC_SATURATION_ARITHMETIC_H
  11 #define _LIBCPP___NUMERIC_SATURATION_ARITHMETIC_H
  12
  13 #include <__concepts/arithmetic.h>
  14 #include <__config>
  15 #include <__utility/cmp.h>
  16 #include <limits>
  17
  18 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  19 #  pragma GCC system_header
  20 #endif
  21
  22 _LIBCPP_PUSH_MACROS
  23 #include <__undef_macros>
  24
  25 _LIBCPP_BEGIN_NAMESPACE_STD
  26
  27 #if _LIBCPP_STD_VER >= 26
  28
  29 template <__libcpp_integer _Tp>
  30 _LIBCPP_HIDE_FROM_ABI constexpr _Tp add_sat(_Tp __x, _Tp __y) noexcept {
  31   if (_Tp __sum; !__builtin_add_overflow(__x, __y, &__sum))
  32     return __sum;
  33   // Handle overflow
  34   if constexpr (__libcpp_unsigned_integer<_Tp>) {
  35     return std::numeric_limits<_Tp>::max();
  36   } else {
  37     // Signed addition overflow
  38     if (__x > 0)
  39       // Overflows if (x > 0 && y > 0)
  40       return std::numeric_limits<_Tp>::max();
  41     else
  42       // Overflows if  (x < 0 && y < 0)
  43       return std::numeric_limits<_Tp>::min();
  44   }
  45 }
  46
  47 template <__libcpp_integer _Tp>
  48 _LIBCPP_HIDE_FROM_ABI constexpr _Tp sub_sat(_Tp __x, _Tp __y) noexcept {
  49   if (_Tp __sub; !__builtin_sub_overflow(__x, __y, &__sub))
  50     return __sub;
  51   // Handle overflow
  52   if constexpr (__libcpp_unsigned_integer<_Tp>) {
  53     // Overflows if (x < y)
  54     return std::numeric_limits<_Tp>::min();
  55   } else {
  56     // Signed subtration overflow
  57     if (__x >= 0)
  58       // Overflows if (x >= 0 && y < 0)
  59       return std::numeric_limits<_Tp>::max();
  60     else
  61       // Overflows if (x < 0 && y > 0)
  62       return std::numeric_limits<_Tp>::min();
  63   }
  64 }
  65
  66 template <__libcpp_integer _Tp>
  67 _LIBCPP_HIDE_FROM_ABI constexpr _Tp mul_sat(_Tp __x, _Tp __y) noexcept {
  68   if (_Tp __mul; !__builtin_mul_overflow(__x, __y, &__mul))
  69     return __mul;
  70   // Handle overflow
  71   if constexpr (__libcpp_unsigned_integer<_Tp>) {
  72     return std::numeric_limits<_Tp>::max();
  73   } else {
  74     // Signed multiplication overflow
  75     if ((__x > 0 && __y > 0) || (__x < 0 && __y < 0))
  76       return std::numeric_limits<_Tp>::max();
  77     // Overflows if (x < 0 && y > 0) || (x > 0 && y < 0)
  78     return std::numeric_limits<_Tp>::min();
  79   }
  80 }
  81
  82 template <__libcpp_integer _Tp>
  83 _LIBCPP_HIDE_FROM_ABI constexpr _Tp div_sat(_Tp __x, _Tp __y) noexcept {
  84   _LIBCPP_ASSERT_UNCATEGORIZED(__y != 0, "Division by 0 is undefined");
  85   if constexpr (__libcpp_unsigned_integer<_Tp>) {
  86     return __x / __y;
  87   } else {
  88     // Handle signed division overflow
  89     if (__x == std::numeric_limits<_Tp>::min() && __y == _Tp{-1})
  90       return std::numeric_limits<_Tp>::max();
  91     return __x / __y;
  92   }
  93 }
  94
  95 template <__libcpp_integer _Rp, __libcpp_integer _Tp>
  96 _LIBCPP_HIDE_FROM_ABI constexpr _Rp saturate_cast(_Tp __x) noexcept {
  97   // Saturation is impossible edge case when ((min _Rp) < (min _Tp) && (max _Rp) > (max _Tp)) and it is expected to be
  98   // optimized out by the compiler.
  99
 100   // Handle overflow
 101   if (std::cmp_less(__x, std::numeric_limits<_Rp>::min()))
 102     return std::numeric_limits<_Rp>::min();
 103   if (std::cmp_greater(__x, std::numeric_limits<_Rp>::max()))
 104     return std::numeric_limits<_Rp>::max();
 105   // No overflow
 106   return static_cast<_Rp>(__x);
 107 }
 108
 109 #endif // _LIBCPP_STD_VER >= 26
 110
 111 _LIBCPP_END_NAMESPACE_STD
 112
 113 _LIBCPP_POP_MACROS
 114
 115 #endif // _LIBCPP___NUMERIC_SATURATION_ARITHMETIC_H