143 lines
4.3 KiB
C++
143 lines
4.3 KiB
C++
/*
|
|
* 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_
|