136 lines
3.9 KiB
C++
136 lines
3.9 KiB
C++
/*
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* Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#ifndef WEBRTC_BASE_MOD_OPS_H_
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#define WEBRTC_BASE_MOD_OPS_H_
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#include <limits>
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#include <type_traits>
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#include "webrtc/base/checks.h"
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namespace webrtc {
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template <unsigned long M> // NOLINT
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inline unsigned long Add(unsigned long a, unsigned long b) { // NOLINT
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RTC_DCHECK_LT(a, M);
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unsigned long t = M - b % M; // NOLINT
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unsigned long res = a - t; // NOLINT
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if (t > a)
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return res + M;
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return res;
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}
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template <unsigned long M> // NOLINT
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inline unsigned long Subtract(unsigned long a, unsigned long b) { // NOLINT
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RTC_DCHECK_LT(a, M);
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unsigned long sub = b % M; // NOLINT
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if (a < sub)
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return M - (sub - a);
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return a - sub;
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}
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// Calculates the forward difference between two wrapping numbers.
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//
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// Example:
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// uint8_t x = 253;
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// uint8_t y = 2;
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//
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// ForwardDiff(x, y) == 4
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//
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// 252 253 254 255 0 1 2 3
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// #################################################
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// | | x | | | | | y | |
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// #################################################
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// |----->----->----->----->----->
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//
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// ForwardDiff(y, x) == 251
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//
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// 252 253 254 255 0 1 2 3
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// #################################################
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// | | x | | | | | y | |
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// #################################################
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// -->-----> |----->---
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//
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template <typename T, T M>
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inline T ForwardDiff(T a, T b) {
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static_assert(std::is_unsigned<T>::value,
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"Type must be an unsigned integer.");
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RTC_DCHECK_LT(a, M);
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RTC_DCHECK_LT(b, M);
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return a <= b ? b - a : M - (a - b);
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}
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template <typename T>
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inline T ForwardDiff(T a, T b) {
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static_assert(std::is_unsigned<T>::value,
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"Type must be an unsigned integer.");
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return b - a;
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}
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// Calculates the reverse difference between two wrapping numbers.
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//
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// Example:
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// uint8_t x = 253;
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// uint8_t y = 2;
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//
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// ReverseDiff(y, x) == 5
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//
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// 252 253 254 255 0 1 2 3
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// #################################################
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// | | x | | | | | y | |
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// #################################################
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// <-----<-----<-----<-----<-----|
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//
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// ReverseDiff(x, y) == 251
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//
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// 252 253 254 255 0 1 2 3
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// #################################################
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// | | x | | | | | y | |
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// #################################################
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// ---<-----| |<-----<--
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//
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template <typename T, T M>
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inline T ReverseDiff(T a, T b) {
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static_assert(std::is_unsigned<T>::value,
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"Type must be an unsigned integer.");
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RTC_DCHECK_LT(a, M);
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RTC_DCHECK_LT(b, M);
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return b <= a ? a - b : M - (b - a);
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}
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template <typename T>
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inline T ReverseDiff(T a, T b) {
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static_assert(std::is_unsigned<T>::value,
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"Type must be an unsigned integer.");
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return a - b;
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}
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// Calculates the minimum distance between to wrapping numbers.
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//
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// The minimum distance is defined as min(ForwardDiff(a, b), ReverseDiff(a, b))
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template <typename T, T M>
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inline T MinDiff(T a, T b) {
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static_assert(std::is_unsigned<T>::value,
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"Type must be an unsigned integer.");
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return std::min(ForwardDiff<T, M>(a, b), ReverseDiff<T, M>(a, b));
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}
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template <typename T>
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inline T MinDiff(T a, T b) {
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static_assert(std::is_unsigned<T>::value,
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"Type must be an unsigned integer.");
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return std::min(ForwardDiff(a, b), ReverseDiff(a, b));
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}
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} // namespace webrtc
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#endif // WEBRTC_BASE_MOD_OPS_H_
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