LLVM 17.0.0git
bit.h
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1//===-- llvm/ADT/bit.h - C++20 <bit> ----------------------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8///
9/// \file
10/// This file implements the C++20 <bit> header.
11///
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_ADT_BIT_H
15#define LLVM_ADT_BIT_H
16
18#include <cstdint>
19#include <limits>
20#include <type_traits>
21
22#if !__has_builtin(__builtin_bit_cast)
23#include <cstring>
24#endif
25
26#if defined(_MSC_VER) && !defined(_DEBUG)
27#include <cstdlib> // for _byteswap_{ushort,ulong,uint64}
28#endif
29
30#ifdef _MSC_VER
31// Declare these intrinsics manually rather including intrin.h. It's very
32// expensive, and bit.h is popular via MathExtras.h.
33// #include <intrin.h>
34extern "C" {
35unsigned char _BitScanForward(unsigned long *_Index, unsigned long _Mask);
36unsigned char _BitScanForward64(unsigned long *_Index, unsigned __int64 _Mask);
37unsigned char _BitScanReverse(unsigned long *_Index, unsigned long _Mask);
38unsigned char _BitScanReverse64(unsigned long *_Index, unsigned __int64 _Mask);
39}
40#endif
41
42namespace llvm {
43
44// This implementation of bit_cast is different from the C++20 one in two ways:
45// - It isn't constexpr because that requires compiler support.
46// - It requires trivially-constructible To, to avoid UB in the implementation.
47template <
48 typename To, typename From,
49 typename = std::enable_if_t<sizeof(To) == sizeof(From)>,
50 typename = std::enable_if_t<std::is_trivially_constructible<To>::value>,
51 typename = std::enable_if_t<std::is_trivially_copyable<To>::value>,
52 typename = std::enable_if_t<std::is_trivially_copyable<From>::value>>
53[[nodiscard]] inline To bit_cast(const From &from) noexcept {
54#if __has_builtin(__builtin_bit_cast)
55 return __builtin_bit_cast(To, from);
56#else
57 To to;
58 std::memcpy(&to, &from, sizeof(To));
59 return to;
60#endif
61}
62
63/// Reverses the bytes in the given integer value V.
64template <typename T, typename = std::enable_if_t<std::is_integral_v<T>>>
65[[nodiscard]] constexpr T byteswap(T V) noexcept {
66 if constexpr (sizeof(T) == 1) {
67 return V;
68 } else if constexpr (sizeof(T) == 2) {
69 uint16_t UV = V;
70#if defined(_MSC_VER) && !defined(_DEBUG)
71 // The DLL version of the runtime lacks these functions (bug!?), but in a
72 // release build they're replaced with BSWAP instructions anyway.
73 return _byteswap_ushort(UV);
74#else
75 uint16_t Hi = UV << 8;
76 uint16_t Lo = UV >> 8;
77 return Hi | Lo;
78#endif
79 } else if constexpr (sizeof(T) == 4) {
80 uint32_t UV = V;
81#if __has_builtin(__builtin_bswap32)
82 return __builtin_bswap32(UV);
83#elif defined(_MSC_VER) && !defined(_DEBUG)
84 return _byteswap_ulong(UV);
85#else
86 uint32_t Byte0 = UV & 0x000000FF;
87 uint32_t Byte1 = UV & 0x0000FF00;
88 uint32_t Byte2 = UV & 0x00FF0000;
89 uint32_t Byte3 = UV & 0xFF000000;
90 return (Byte0 << 24) | (Byte1 << 8) | (Byte2 >> 8) | (Byte3 >> 24);
91#endif
92 } else if constexpr (sizeof(T) == 8) {
93 uint64_t UV = V;
94#if __has_builtin(__builtin_bswap64)
95 return __builtin_bswap64(UV);
96#elif defined(_MSC_VER) && !defined(_DEBUG)
97 return _byteswap_uint64(UV);
98#else
99 uint64_t Hi = llvm::byteswap<uint32_t>(UV);
100 uint32_t Lo = llvm::byteswap<uint32_t>(UV >> 32);
101 return (Hi << 32) | Lo;
102#endif
103 } else {
104 static_assert(!sizeof(T *), "Don't know how to handle the given type.");
105 return 0;
106 }
107}
108
109template <typename T, typename = std::enable_if_t<std::is_unsigned_v<T>>>
110[[nodiscard]] constexpr inline bool has_single_bit(T Value) noexcept {
111 return (Value != 0) && ((Value & (Value - 1)) == 0);
112}
113
114namespace detail {
115template <typename T, std::size_t SizeOfT> struct TrailingZerosCounter {
116 static unsigned count(T Val) {
117 if (!Val)
118 return std::numeric_limits<T>::digits;
119 if (Val & 0x1)
120 return 0;
121
122 // Bisection method.
123 unsigned ZeroBits = 0;
124 T Shift = std::numeric_limits<T>::digits >> 1;
125 T Mask = std::numeric_limits<T>::max() >> Shift;
126 while (Shift) {
127 if ((Val & Mask) == 0) {
128 Val >>= Shift;
129 ZeroBits |= Shift;
130 }
131 Shift >>= 1;
132 Mask >>= Shift;
133 }
134 return ZeroBits;
135 }
136};
137
138#if defined(__GNUC__) || defined(_MSC_VER)
139template <typename T> struct TrailingZerosCounter<T, 4> {
140 static unsigned count(T Val) {
141 if (Val == 0)
142 return 32;
143
144#if __has_builtin(__builtin_ctz) || defined(__GNUC__)
145 return __builtin_ctz(Val);
146#elif defined(_MSC_VER)
147 unsigned long Index;
148 _BitScanForward(&Index, Val);
149 return Index;
150#endif
151 }
152};
153
154#if !defined(_MSC_VER) || defined(_M_X64)
155template <typename T> struct TrailingZerosCounter<T, 8> {
156 static unsigned count(T Val) {
157 if (Val == 0)
158 return 64;
159
160#if __has_builtin(__builtin_ctzll) || defined(__GNUC__)
161 return __builtin_ctzll(Val);
162#elif defined(_MSC_VER)
163 unsigned long Index;
164 _BitScanForward64(&Index, Val);
165 return Index;
166#endif
167 }
168};
169#endif
170#endif
171} // namespace detail
172
173/// Count number of 0's from the least significant bit to the most
174/// stopping at the first 1.
175///
176/// Only unsigned integral types are allowed.
177///
178/// Returns std::numeric_limits<T>::digits on an input of 0.
179template <typename T> [[nodiscard]] int countr_zero(T Val) {
180 static_assert(std::is_unsigned_v<T>,
181 "Only unsigned integral types are allowed.");
182 return llvm::detail::TrailingZerosCounter<T, sizeof(T)>::count(Val);
183}
184
185namespace detail {
186template <typename T, std::size_t SizeOfT> struct LeadingZerosCounter {
187 static unsigned count(T Val) {
188 if (!Val)
189 return std::numeric_limits<T>::digits;
190
191 // Bisection method.
192 unsigned ZeroBits = 0;
193 for (T Shift = std::numeric_limits<T>::digits >> 1; Shift; Shift >>= 1) {
194 T Tmp = Val >> Shift;
195 if (Tmp)
196 Val = Tmp;
197 else
198 ZeroBits |= Shift;
199 }
200 return ZeroBits;
201 }
202};
203
204#if defined(__GNUC__) || defined(_MSC_VER)
205template <typename T> struct LeadingZerosCounter<T, 4> {
206 static unsigned count(T Val) {
207 if (Val == 0)
208 return 32;
209
210#if __has_builtin(__builtin_clz) || defined(__GNUC__)
211 return __builtin_clz(Val);
212#elif defined(_MSC_VER)
213 unsigned long Index;
214 _BitScanReverse(&Index, Val);
215 return Index ^ 31;
216#endif
217 }
218};
219
220#if !defined(_MSC_VER) || defined(_M_X64)
221template <typename T> struct LeadingZerosCounter<T, 8> {
222 static unsigned count(T Val) {
223 if (Val == 0)
224 return 64;
225
226#if __has_builtin(__builtin_clzll) || defined(__GNUC__)
227 return __builtin_clzll(Val);
228#elif defined(_MSC_VER)
229 unsigned long Index;
230 _BitScanReverse64(&Index, Val);
231 return Index ^ 63;
232#endif
233 }
234};
235#endif
236#endif
237} // namespace detail
238
239/// Count number of 0's from the most significant bit to the least
240/// stopping at the first 1.
241///
242/// Only unsigned integral types are allowed.
243///
244/// Returns std::numeric_limits<T>::digits on an input of 0.
245template <typename T> [[nodiscard]] int countl_zero(T Val) {
246 static_assert(std::is_unsigned_v<T>,
247 "Only unsigned integral types are allowed.");
248 return llvm::detail::LeadingZerosCounter<T, sizeof(T)>::count(Val);
249}
250
251/// Count the number of ones from the most significant bit to the first
252/// zero bit.
253///
254/// Ex. countl_one(0xFF0FFF00) == 8.
255/// Only unsigned integral types are allowed.
256///
257/// Returns std::numeric_limits<T>::digits on an input of all ones.
258template <typename T> [[nodiscard]] int countl_one(T Value) {
259 static_assert(std::is_unsigned_v<T>,
260 "Only unsigned integral types are allowed.");
261 return llvm::countl_zero<T>(~Value);
262}
263
264/// Count the number of ones from the least significant bit to the first
265/// zero bit.
266///
267/// Ex. countr_one(0x00FF00FF) == 8.
268/// Only unsigned integral types are allowed.
269///
270/// Returns std::numeric_limits<T>::digits on an input of all ones.
271template <typename T> [[nodiscard]] int countr_one(T Value) {
272 static_assert(std::is_unsigned_v<T>,
273 "Only unsigned integral types are allowed.");
274 return llvm::countr_zero<T>(~Value);
275}
276
277/// Returns the number of bits needed to represent Value if Value is nonzero.
278/// Returns 0 otherwise.
279///
280/// Ex. bit_width(5) == 3.
281template <typename T> [[nodiscard]] int bit_width(T Value) {
282 static_assert(std::is_unsigned_v<T>,
283 "Only unsigned integral types are allowed.");
284 return std::numeric_limits<T>::digits - llvm::countl_zero(Value);
285}
286
287/// Returns the largest integral power of two no greater than Value if Value is
288/// nonzero. Returns 0 otherwise.
289///
290/// Ex. bit_floor(5) == 4.
291template <typename T> [[nodiscard]] T bit_floor(T Value) {
292 static_assert(std::is_unsigned_v<T>,
293 "Only unsigned integral types are allowed.");
294 if (!Value)
295 return 0;
296 return T(1) << (llvm::bit_width(Value) - 1);
297}
298
299/// Returns the smallest integral power of two no smaller than Value if Value is
300/// nonzero. Returns 1 otherwise.
301///
302/// Ex. bit_ceil(5) == 8.
303///
304/// The return value is undefined if the input is larger than the largest power
305/// of two representable in T.
306template <typename T> [[nodiscard]] T bit_ceil(T Value) {
307 static_assert(std::is_unsigned_v<T>,
308 "Only unsigned integral types are allowed.");
309 if (Value < 2)
310 return 1;
311 return T(1) << llvm::bit_width<T>(Value - 1u);
312}
313
314namespace detail {
315template <typename T, std::size_t SizeOfT> struct PopulationCounter {
316 static int count(T Value) {
317 // Generic version, forward to 32 bits.
318 static_assert(SizeOfT <= 4, "Not implemented!");
319#if defined(__GNUC__)
320 return (int)__builtin_popcount(Value);
321#else
322 uint32_t v = Value;
323 v = v - ((v >> 1) & 0x55555555);
324 v = (v & 0x33333333) + ((v >> 2) & 0x33333333);
325 return int(((v + (v >> 4) & 0xF0F0F0F) * 0x1010101) >> 24);
326#endif
327 }
328};
329
330template <typename T> struct PopulationCounter<T, 8> {
331 static int count(T Value) {
332#if defined(__GNUC__)
333 return (int)__builtin_popcountll(Value);
334#else
335 uint64_t v = Value;
336 v = v - ((v >> 1) & 0x5555555555555555ULL);
337 v = (v & 0x3333333333333333ULL) + ((v >> 2) & 0x3333333333333333ULL);
338 v = (v + (v >> 4)) & 0x0F0F0F0F0F0F0F0FULL;
339 return int((uint64_t)(v * 0x0101010101010101ULL) >> 56);
340#endif
341 }
342};
343} // namespace detail
344
345/// Count the number of set bits in a value.
346/// Ex. popcount(0xF000F000) = 8
347/// Returns 0 if the word is zero.
348template <typename T, typename = std::enable_if_t<std::is_unsigned_v<T>>>
349[[nodiscard]] inline int popcount(T Value) noexcept {
350 return detail::PopulationCounter<T, sizeof(T)>::count(Value);
351}
352
353} // namespace llvm
354
355#endif
BlockVerifier::State From
#define T
LLVM Value Representation.
Definition: Value.h:74
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
int popcount(T Value) noexcept
Count the number of set bits in a value.
Definition: bit.h:349
int countr_one(T Value)
Count the number of ones from the least significant bit to the first zero bit.
Definition: bit.h:271
constexpr T byteswap(T V) noexcept
Reverses the bytes in the given integer value V.
Definition: bit.h:65
int bit_width(T Value)
Returns the number of bits needed to represent Value if Value is nonzero.
Definition: bit.h:281
T bit_ceil(T Value)
Returns the smallest integral power of two no smaller than Value if Value is nonzero.
Definition: bit.h:306
int countr_zero(T Val)
Count number of 0's from the least significant bit to the most stopping at the first 1.
Definition: bit.h:179
constexpr bool has_single_bit(T Value) noexcept
Definition: bit.h:110
int countl_zero(T Val)
Count number of 0's from the most significant bit to the least stopping at the first 1.
Definition: bit.h:245
int countl_one(T Value)
Count the number of ones from the most significant bit to the first zero bit.
Definition: bit.h:258
To bit_cast(const From &from) noexcept
Definition: bit.h:53
auto count(R &&Range, const E &Element)
Wrapper function around std::count to count the number of times an element Element occurs in the give...
Definition: STLExtras.h:1896
T bit_floor(T Value)
Returns the largest integral power of two no greater than Value if Value is nonzero.
Definition: bit.h:291
static unsigned count(T Val)
Definition: bit.h:187
static int count(T Value)
Definition: bit.h:331
static int count(T Value)
Definition: bit.h:316
static unsigned count(T Val)
Definition: bit.h:116