1 /*
2 * Copyright 2005 The WebRTC Project Authors. All rights reserved.
3 *
4 * Use of this source code is governed by a BSD-style license
5 * that can be found in the LICENSE file in the root of the source
6 * tree. An additional intellectual property rights grant can be found
7 * in the file PATENTS. All contributing project authors may
8 * be found in the AUTHORS file in the root of the source tree.
9 */
10
11 #ifndef API_NUMERICS_MATH_UTILS_H_
12 #define API_NUMERICS_MATH_UTILS_H_
13
14 #include <limits>
15 #include <type_traits>
16
17 #include "rtc_base/checks.h"
18
19 namespace webrtc {
20 namespace webrtc_impl {
21 // Given two numbers `x` and `y` such that x >= y, computes the difference
22 // x - y without causing undefined behavior due to signed overflow.
23 template <typename T>
unsigned_difference(T x,T y)24 typename std::make_unsigned<T>::type unsigned_difference(T x, T y) {
25 static_assert(
26 std::is_signed<T>::value,
27 "Function unsigned_difference is only meaningful for signed types.");
28 RTC_DCHECK_GE(x, y);
29 typedef typename std::make_unsigned<T>::type unsigned_type;
30 // int -> unsigned conversion repeatedly adds UINT_MAX + 1 until the number
31 // can be represented as an unsigned. Since we know that the actual
32 // difference x - y can be represented as an unsigned, it is sufficient to
33 // compute the difference modulo UINT_MAX + 1, i.e using unsigned arithmetic.
34 return static_cast<unsigned_type>(x) - static_cast<unsigned_type>(y);
35 }
36
37 // Provide neutral element with respect to min().
38 // Typically used as an initial value for running minimum.
39 template <typename T,
40 typename std::enable_if<std::numeric_limits<T>::has_infinity>::type* =
41 nullptr>
infinity_or_max()42 constexpr T infinity_or_max() {
43 return std::numeric_limits<T>::infinity();
44 }
45
46 template <typename T,
47 typename std::enable_if<
48 !std::numeric_limits<T>::has_infinity>::type* = nullptr>
infinity_or_max()49 constexpr T infinity_or_max() {
50 // Fallback to max().
51 return std::numeric_limits<T>::max();
52 }
53
54 // Provide neutral element with respect to max().
55 // Typically used as an initial value for running maximum.
56 template <typename T,
57 typename std::enable_if<std::numeric_limits<T>::has_infinity>::type* =
58 nullptr>
minus_infinity_or_min()59 constexpr T minus_infinity_or_min() {
60 static_assert(std::is_signed<T>::value, "Unsupported. Please open a bug.");
61 return -std::numeric_limits<T>::infinity();
62 }
63
64 template <typename T,
65 typename std::enable_if<
66 !std::numeric_limits<T>::has_infinity>::type* = nullptr>
minus_infinity_or_min()67 constexpr T minus_infinity_or_min() {
68 // Fallback to min().
69 return std::numeric_limits<T>::min();
70 }
71
72 } // namespace webrtc_impl
73 } // namespace webrtc
74
75 #endif // API_NUMERICS_MATH_UTILS_H_
76