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Diffstat (limited to 'third_party/libwebrtc/rtc_base/numerics/mod_ops.h')
| -rw-r--r-- | third_party/libwebrtc/rtc_base/numerics/mod_ops.h | 142 |
1 files changed, 142 insertions, 0 deletions
diff --git a/third_party/libwebrtc/rtc_base/numerics/mod_ops.h b/third_party/libwebrtc/rtc_base/numerics/mod_ops.h new file mode 100644 index 0000000000..65618b4876 --- /dev/null +++ b/third_party/libwebrtc/rtc_base/numerics/mod_ops.h @@ -0,0 +1,142 @@ +/* + * 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_ |