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/*
* Copyright 2005 The WebRTC Project Authors. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef API_NUMERICS_MATH_UTILS_H_
#define API_NUMERICS_MATH_UTILS_H_
#include <limits>
#include <type_traits>
#include "rtc_base/checks.h"
namespace webrtc {
namespace webrtc_impl {
// Given two numbers `x` and `y` such that x >= y, computes the difference
// x - y without causing undefined behavior due to signed overflow.
template <typename T>
typename std::make_unsigned<T>::type unsigned_difference(T x, T y) {
static_assert(
std::is_signed<T>::value,
"Function unsigned_difference is only meaningful for signed types.");
RTC_DCHECK_GE(x, y);
typedef typename std::make_unsigned<T>::type unsigned_type;
// int -> unsigned conversion repeatedly adds UINT_MAX + 1 until the number
// can be represented as an unsigned. Since we know that the actual
// difference x - y can be represented as an unsigned, it is sufficient to
// compute the difference modulo UINT_MAX + 1, i.e using unsigned arithmetic.
return static_cast<unsigned_type>(x) - static_cast<unsigned_type>(y);
}
// Provide neutral element with respect to min().
// Typically used as an initial value for running minimum.
template <typename T,
typename std::enable_if<std::numeric_limits<T>::has_infinity>::type* =
nullptr>
constexpr T infinity_or_max() {
return std::numeric_limits<T>::infinity();
}
template <typename T,
typename std::enable_if<
!std::numeric_limits<T>::has_infinity>::type* = nullptr>
constexpr T infinity_or_max() {
// Fallback to max().
return std::numeric_limits<T>::max();
}
// Provide neutral element with respect to max().
// Typically used as an initial value for running maximum.
template <typename T,
typename std::enable_if<std::numeric_limits<T>::has_infinity>::type* =
nullptr>
constexpr T minus_infinity_or_min() {
static_assert(std::is_signed<T>::value, "Unsupported. Please open a bug.");
return -std::numeric_limits<T>::infinity();
}
template <typename T,
typename std::enable_if<
!std::numeric_limits<T>::has_infinity>::type* = nullptr>
constexpr T minus_infinity_or_min() {
// Fallback to min().
return std::numeric_limits<T>::min();
}
} // namespace webrtc_impl
} // namespace webrtc
#endif // API_NUMERICS_MATH_UTILS_H_
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