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/*
* Copyright (c) 2016 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 RTC_BASE_NUMERICS_MOD_OPS_H_
#define RTC_BASE_NUMERICS_MOD_OPS_H_
#include <algorithm>
#include <type_traits>
#include "rtc_base/checks.h"
namespace webrtc {
template <unsigned long M> // NOLINT
inline unsigned long Add(unsigned long a, unsigned long b) { // NOLINT
RTC_DCHECK_LT(a, M);
unsigned long t = M - b % M; // NOLINT
unsigned long res = a - t; // NOLINT
if (t > a)
return res + M;
return res;
}
template <unsigned long M> // NOLINT
inline unsigned long Subtract(unsigned long a, unsigned long b) { // NOLINT
RTC_DCHECK_LT(a, M);
unsigned long sub = b % M; // NOLINT
if (a < sub)
return M - (sub - a);
return a - sub;
}
// Calculates the forward difference between two wrapping numbers.
//
// Example:
// uint8_t x = 253;
// uint8_t y = 2;
//
// ForwardDiff(x, y) == 5
//
// 252 253 254 255 0 1 2 3
// #################################################
// | | x | | | | | y | |
// #################################################
// |----->----->----->----->----->
//
// ForwardDiff(y, x) == 251
//
// 252 253 254 255 0 1 2 3
// #################################################
// | | x | | | | | y | |
// #################################################
// -->-----> |----->---
//
// If M > 0 then wrapping occurs at M, if M == 0 then wrapping occurs at the
// largest value representable by T.
template <typename T, T M>
inline typename std::enable_if<(M > 0), T>::type ForwardDiff(T a, T b) {
static_assert(std::is_unsigned<T>::value,
"Type must be an unsigned integer.");
RTC_DCHECK_LT(a, M);
RTC_DCHECK_LT(b, M);
return a <= b ? b - a : M - (a - b);
}
template <typename T, T M>
inline typename std::enable_if<(M == 0), T>::type ForwardDiff(T a, T b) {
static_assert(std::is_unsigned<T>::value,
"Type must be an unsigned integer.");
return b - a;
}
template <typename T>
inline T ForwardDiff(T a, T b) {
return ForwardDiff<T, 0>(a, b);
}
// Calculates the reverse difference between two wrapping numbers.
//
// Example:
// uint8_t x = 253;
// uint8_t y = 2;
//
// ReverseDiff(y, x) == 5
//
// 252 253 254 255 0 1 2 3
// #################################################
// | | x | | | | | y | |
// #################################################
// <-----<-----<-----<-----<-----|
//
// ReverseDiff(x, y) == 251
//
// 252 253 254 255 0 1 2 3
// #################################################
// | | x | | | | | y | |
// #################################################
// ---<-----| |<-----<--
//
// If M > 0 then wrapping occurs at M, if M == 0 then wrapping occurs at the
// largest value representable by T.
template <typename T, T M>
inline typename std::enable_if<(M > 0), T>::type ReverseDiff(T a, T b) {
static_assert(std::is_unsigned<T>::value,
"Type must be an unsigned integer.");
RTC_DCHECK_LT(a, M);
RTC_DCHECK_LT(b, M);
return b <= a ? a - b : M - (b - a);
}
template <typename T, T M>
inline typename std::enable_if<(M == 0), T>::type ReverseDiff(T a, T b) {
static_assert(std::is_unsigned<T>::value,
"Type must be an unsigned integer.");
return a - b;
}
template <typename T>
inline T ReverseDiff(T a, T b) {
return ReverseDiff<T, 0>(a, b);
}
// Calculates the minimum distance between to wrapping numbers.
//
// The minimum distance is defined as min(ForwardDiff(a, b), ReverseDiff(a, b))
template <typename T, T M = 0>
inline T MinDiff(T a, T b) {
static_assert(std::is_unsigned<T>::value,
"Type must be an unsigned integer.");
return std::min(ForwardDiff<T, M>(a, b), ReverseDiff<T, M>(a, b));
}
} // namespace webrtc
#endif // RTC_BASE_NUMERICS_MOD_OPS_H_
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