OpenTTD Source: src/core/bitmath_func.hpp Source File

OpenTTD Source 15.3

bitmath_func.hpp
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1/*
2 * This file is part of OpenTTD.
3 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
4 * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
5 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <https://www.gnu.org/licenses/old-licenses/gpl-2.0>.
6 */
7
10#ifndef BITMATH_FUNC_HPP
11#define BITMATH_FUNC_HPP
12
31template <typename T>
32[[debug_inline]] inline constexpr static uint GB(const T x, const uint8_t s, const uint8_t n)
33{
34 return (x >> s) & (((T)1U << n) - 1);
35}
36
57template <typename T, typename U>
58 constexpr T SB(T &x, const uint8_t s, const uint8_t n, const U d)
59{
60 x &= (T)(~((((T)1U << n) - 1) << s));
61 x |= (T)(d << s);
62 return x;
63}
64
82template <typename T, typename U>
83 constexpr T AB(T &x, const uint8_t s, const uint8_t n, const U i)
84{
85 const T mask = ((((T)1U << n) - 1) << s);
86 x = (T)((x & ~mask) | ((x + (i << s)) & mask));
87 return x;
88}
89
102template <typename T>
103[[debug_inline]] inline constexpr bool HasBit(const T x, const uint8_t y)
104{
105 return (x & ((T)1U << y)) != 0;
106}
107
120template <typename T>
121 constexpr T SetBit(T &x, const uint8_t y)
122{
123 return x = (T)(x | ((T)1U << y));
124}
125
138template <typename T>
139 constexpr T ClrBit(T &x, const uint8_t y)
140{
141 return x = (T)(x & ~((T)1U << y));
142}
143
156template <typename T>
157 constexpr T ToggleBit(T &x, const uint8_t y)
158{
159 return x = (T)(x ^ ((T)1U << y));
160}
161
175template <typename T>
176 constexpr T AssignBit(T &x, const uint8_t y, bool value)
177{
178 return SB<T>(x, y, 1, value ? 1 : 0);
179}
180
188template <typename T>
189 constexpr uint8_t FindFirstBit(T x)
190{
191 if (x == 0) return 0;
192
193 if constexpr (std::is_enum_v<T>) {
194 return std::countr_zero<std::underlying_type_t<T>>(x);
195 } else {
196 return std::countr_zero(x);
197 }
198}
199
207template <typename T>
208 constexpr uint8_t FindLastBit(T x)
209{
210 if (x == 0) return 0;
211
212 return std::numeric_limits<T>::digits - std::countl_zero(x) - 1;
213}
214
225template <typename T>
226 constexpr T KillFirstBit(T value)
227{
228 return value &= (T)(value - 1);
229}
230
237template <typename T>
238 constexpr uint CountBits(T value)
239{
240 if constexpr (std::is_enum_v<T>) {
241 return std::popcount<std::underlying_type_t<T>>(value);
242 } else {
243 return std::popcount(value);
244 }
245}
246
253template <typename T>
254 constexpr bool HasExactlyOneBit(T value)
255{
256 return value != 0 && (value & (value - 1)) == 0;
257}
258
265template <typename T>
266 constexpr bool HasAtMostOneBit(T value)
267{
268 return (value & (value - 1)) == 0;
269}
270
276template <typename Tbitpos = uint, typename Tbitset = uint>
277 struct SetBitIterator {
278 struct Iterator {
279 typedef Tbitpos value_type;
280 typedef value_type *pointer;
281 typedef value_type &reference;
282 typedef size_t difference_type;
283 typedef std::forward_iterator_tag iterator_category;
284
285 explicit Iterator(Tbitset bitset) : bitset(bitset), bitpos(static_cast<Tbitpos>(0))
286 {
287 this->Validate();
288 }
289
290 bool operator==(const Iterator &other) const
291 {
292 return this->bitset == other.bitset;
293 }
294 Tbitpos operator*() const { return this->bitpos; }
295 Iterator & operator++() { this->Next(); this->Validate(); return *this; }
296
297 private:
298 Tbitset bitset;
299 Tbitpos bitpos;
300 void Validate()
301 {
302 if (this->bitset != 0) {
303 typename std::make_unsigned<Tbitset>::type unsigned_value = this->bitset;
304 this->bitpos = static_cast<Tbitpos>(FindFirstBit(unsigned_value));
305 }
306 }
307 void Next()
308 {
309 this->bitset = KillFirstBit(this->bitset);
310 }
311 };
312
313 SetBitIterator(Tbitset bitset) : bitset(bitset) {}
314 Iterator begin() { return Iterator(this->bitset); }
315 Iterator end() { return Iterator(static_cast<Tbitset>(0)); }
316 bool empty() { return this->begin() == this->end(); }
317
318private:
319 Tbitset bitset;
320};
321
322namespace std {
329 template <typename T>
330 [[nodiscard]] constexpr enable_if_t<is_integral_v<T>, T> byteswap(T x) noexcept
331 {
332 if constexpr (sizeof(T) == 1) return x;
333 if constexpr (sizeof(T) == 2) return (x >> 8) | (x << 8);
334 if constexpr (sizeof(T) == 4) return ((x >> 24) & 0xFF) | ((x >> 8) & 0xFF00) | ((x << 8) & 0xFF0000) | ((x << 24) & 0xFF000000);
335 }
336}
337
338#endif /* BITMATH_FUNC_HPP */
HasExactlyOneBit
constexpr bool HasExactlyOneBit(T value)
Test whether value has exactly 1 bit set.
Definition bitmath_func.hpp:254
AssignBit
constexpr T AssignBit(T &x, const uint8_t y, bool value)
Assigns a bit in a variable.
Definition bitmath_func.hpp:176
SB
constexpr T SB(T &x, const uint8_t s, const uint8_t n, const U d)
Set n bits in x starting at bit s to d.
Definition bitmath_func.hpp:58
GB
static constexpr uint GB(const T x, const uint8_t s, const uint8_t n)
Fetch n bits from x, started at bit s.
Definition bitmath_func.hpp:32
FindLastBit
constexpr uint8_t FindLastBit(T x)
Search the last set bit in a value.
Definition bitmath_func.hpp:208
SetBit
constexpr T SetBit(T &x, const uint8_t y)
Set a bit in a variable.
Definition bitmath_func.hpp:121
FindFirstBit
constexpr uint8_t FindFirstBit(T x)
Search the first set bit in a value.
Definition bitmath_func.hpp:189
CountBits
constexpr uint CountBits(T value)
Counts the number of set bits in a variable.
Definition bitmath_func.hpp:238
HasBit
constexpr bool HasBit(const T x, const uint8_t y)
Checks if a bit in a value is set.
Definition bitmath_func.hpp:103
HasAtMostOneBit
constexpr bool HasAtMostOneBit(T value)
Test whether value has at most 1 bit set.
Definition bitmath_func.hpp:266
AB
constexpr T AB(T &x, const uint8_t s, const uint8_t n, const U i)
Add i to n bits of x starting at bit s.
Definition bitmath_func.hpp:83
std::byteswap
constexpr enable_if_t< is_integral_v< T >, T > byteswap(T x) noexcept
Custom implementation of std::byteswap; remove once we build with C++23.
Definition bitmath_func.hpp:330
ToggleBit
constexpr T ToggleBit(T &x, const uint8_t y)
Toggles a bit in a variable.
Definition bitmath_func.hpp:157
KillFirstBit
constexpr T KillFirstBit(T value)
Clear the first bit in an integer.
Definition bitmath_func.hpp:226
ClrBit
constexpr T ClrBit(T &x, const uint8_t y)
Clears a bit in a variable.
Definition bitmath_func.hpp:139
SetBitIterator::Iterator
Definition bitmath_func.hpp:278
SetBitIterator
Iterable ensemble of each set bit in a value.
Definition bitmath_func.hpp:277