1 /*
2 * Copyright (C) 2015 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #ifndef ART_RUNTIME_BASE_BIT_UTILS_H_
18 #define ART_RUNTIME_BASE_BIT_UTILS_H_
19
20 #include <iterator>
21 #include <limits>
22 #include <type_traits>
23
24 #include "base/iteration_range.h"
25 #include "base/logging.h"
26 #include "base/stl_util.h"
27
28 namespace art {
29
30 // Like sizeof, but count how many bits a type takes. Pass type explicitly.
31 template <typename T>
BitSizeOf()32 constexpr size_t BitSizeOf() {
33 static_assert(std::is_integral<T>::value, "T must be integral");
34 using unsigned_type = typename std::make_unsigned<T>::type;
35 static_assert(sizeof(T) == sizeof(unsigned_type), "Unexpected type size mismatch!");
36 static_assert(std::numeric_limits<unsigned_type>::radix == 2, "Unexpected radix!");
37 return std::numeric_limits<unsigned_type>::digits;
38 }
39
40 // Like sizeof, but count how many bits a type takes. Infers type from parameter.
41 template <typename T>
BitSizeOf(T)42 constexpr size_t BitSizeOf(T /*x*/) {
43 return BitSizeOf<T>();
44 }
45
46 template<typename T>
CLZ(T x)47 constexpr int CLZ(T x) {
48 static_assert(std::is_integral<T>::value, "T must be integral");
49 static_assert(std::is_unsigned<T>::value, "T must be unsigned");
50 static_assert(sizeof(T) <= sizeof(long long), // NOLINT [runtime/int] [4]
51 "T too large, must be smaller than long long");
52 DCHECK_NE(x, 0u);
53 return (sizeof(T) == sizeof(uint32_t)) ? __builtin_clz(x) : __builtin_clzll(x);
54 }
55
56 // Similar to CLZ except that on zero input it returns bitwidth and supports signed integers.
57 template<typename T>
JAVASTYLE_CLZ(T x)58 constexpr int JAVASTYLE_CLZ(T x) {
59 static_assert(std::is_integral<T>::value, "T must be integral");
60 using unsigned_type = typename std::make_unsigned<T>::type;
61 return (x == 0) ? BitSizeOf<T>() : CLZ(static_cast<unsigned_type>(x));
62 }
63
64 template<typename T>
CTZ(T x)65 constexpr int CTZ(T x) {
66 static_assert(std::is_integral<T>::value, "T must be integral");
67 // It is not unreasonable to ask for trailing zeros in a negative number. As such, do not check
68 // that T is an unsigned type.
69 static_assert(sizeof(T) <= sizeof(long long), // NOLINT [runtime/int] [4]
70 "T too large, must be smaller than long long");
71 DCHECK_NE(x, static_cast<T>(0));
72 return (sizeof(T) == sizeof(uint32_t)) ? __builtin_ctz(x) : __builtin_ctzll(x);
73 }
74
75 // Similar to CTZ except that on zero input it returns bitwidth and supports signed integers.
76 template<typename T>
JAVASTYLE_CTZ(T x)77 constexpr int JAVASTYLE_CTZ(T x) {
78 static_assert(std::is_integral<T>::value, "T must be integral");
79 using unsigned_type = typename std::make_unsigned<T>::type;
80 return (x == 0) ? BitSizeOf<T>() : CTZ(static_cast<unsigned_type>(x));
81 }
82
83 // Return the number of 1-bits in `x`.
84 template<typename T>
POPCOUNT(T x)85 constexpr int POPCOUNT(T x) {
86 return (sizeof(T) == sizeof(uint32_t)) ? __builtin_popcount(x) : __builtin_popcountll(x);
87 }
88
89 // Swap bytes.
90 template<typename T>
BSWAP(T x)91 constexpr T BSWAP(T x) {
92 if (sizeof(T) == sizeof(uint16_t)) {
93 return __builtin_bswap16(x);
94 } else if (sizeof(T) == sizeof(uint32_t)) {
95 return __builtin_bswap32(x);
96 } else {
97 return __builtin_bswap64(x);
98 }
99 }
100
101 // Find the bit position of the most significant bit (0-based), or -1 if there were no bits set.
102 template <typename T>
MostSignificantBit(T value)103 constexpr ssize_t MostSignificantBit(T value) {
104 static_assert(std::is_integral<T>::value, "T must be integral");
105 static_assert(std::is_unsigned<T>::value, "T must be unsigned");
106 static_assert(std::numeric_limits<T>::radix == 2, "Unexpected radix!");
107 return (value == 0) ? -1 : std::numeric_limits<T>::digits - 1 - CLZ(value);
108 }
109
110 // Find the bit position of the least significant bit (0-based), or -1 if there were no bits set.
111 template <typename T>
LeastSignificantBit(T value)112 constexpr ssize_t LeastSignificantBit(T value) {
113 static_assert(std::is_integral<T>::value, "T must be integral");
114 static_assert(std::is_unsigned<T>::value, "T must be unsigned");
115 return (value == 0) ? -1 : CTZ(value);
116 }
117
118 // How many bits (minimally) does it take to store the constant 'value'? i.e. 1 for 1, 3 for 5, etc.
119 template <typename T>
MinimumBitsToStore(T value)120 constexpr size_t MinimumBitsToStore(T value) {
121 return static_cast<size_t>(MostSignificantBit(value) + 1);
122 }
123
124 template <typename T>
RoundUpToPowerOfTwo(T x)125 constexpr T RoundUpToPowerOfTwo(T x) {
126 static_assert(std::is_integral<T>::value, "T must be integral");
127 static_assert(std::is_unsigned<T>::value, "T must be unsigned");
128 // NOTE: Undefined if x > (1 << (std::numeric_limits<T>::digits - 1)).
129 return (x < 2u) ? x : static_cast<T>(1u) << (std::numeric_limits<T>::digits - CLZ(x - 1u));
130 }
131
132 template<typename T>
IsPowerOfTwo(T x)133 constexpr bool IsPowerOfTwo(T x) {
134 static_assert(std::is_integral<T>::value, "T must be integral");
135 // TODO: assert unsigned. There is currently many uses with signed values.
136 return (x & (x - 1)) == 0;
137 }
138
139 template<typename T>
WhichPowerOf2(T x)140 constexpr int WhichPowerOf2(T x) {
141 static_assert(std::is_integral<T>::value, "T must be integral");
142 // TODO: assert unsigned. There is currently many uses with signed values.
143 DCHECK((x != 0) && IsPowerOfTwo(x));
144 return CTZ(x);
145 }
146
147 // For rounding integers.
148 // Note: Omit the `n` from T type deduction, deduce only from the `x` argument.
149 template<typename T>
150 constexpr T RoundDown(T x, typename Identity<T>::type n) WARN_UNUSED;
151
152 template<typename T>
RoundDown(T x,typename Identity<T>::type n)153 constexpr T RoundDown(T x, typename Identity<T>::type n) {
154 DCHECK(IsPowerOfTwo(n));
155 return (x & -n);
156 }
157
158 template<typename T>
159 constexpr T RoundUp(T x, typename std::remove_reference<T>::type n) WARN_UNUSED;
160
161 template<typename T>
RoundUp(T x,typename std::remove_reference<T>::type n)162 constexpr T RoundUp(T x, typename std::remove_reference<T>::type n) {
163 return RoundDown(x + n - 1, n);
164 }
165
166 // For aligning pointers.
167 template<typename T>
168 inline T* AlignDown(T* x, uintptr_t n) WARN_UNUSED;
169
170 template<typename T>
AlignDown(T * x,uintptr_t n)171 inline T* AlignDown(T* x, uintptr_t n) {
172 return reinterpret_cast<T*>(RoundDown(reinterpret_cast<uintptr_t>(x), n));
173 }
174
175 template<typename T>
176 inline T* AlignUp(T* x, uintptr_t n) WARN_UNUSED;
177
178 template<typename T>
AlignUp(T * x,uintptr_t n)179 inline T* AlignUp(T* x, uintptr_t n) {
180 return reinterpret_cast<T*>(RoundUp(reinterpret_cast<uintptr_t>(x), n));
181 }
182
183 template<int n, typename T>
IsAligned(T x)184 constexpr bool IsAligned(T x) {
185 static_assert((n & (n - 1)) == 0, "n is not a power of two");
186 return (x & (n - 1)) == 0;
187 }
188
189 template<int n, typename T>
IsAligned(T * x)190 inline bool IsAligned(T* x) {
191 return IsAligned<n>(reinterpret_cast<const uintptr_t>(x));
192 }
193
194 template<typename T>
IsAlignedParam(T x,int n)195 inline bool IsAlignedParam(T x, int n) {
196 return (x & (n - 1)) == 0;
197 }
198
199 template<typename T>
IsAlignedParam(T * x,int n)200 inline bool IsAlignedParam(T* x, int n) {
201 return IsAlignedParam(reinterpret_cast<const uintptr_t>(x), n);
202 }
203
204 #define CHECK_ALIGNED(value, alignment) \
205 CHECK(::art::IsAligned<alignment>(value)) << reinterpret_cast<const void*>(value)
206
207 #define DCHECK_ALIGNED(value, alignment) \
208 DCHECK(::art::IsAligned<alignment>(value)) << reinterpret_cast<const void*>(value)
209
210 #define CHECK_ALIGNED_PARAM(value, alignment) \
211 CHECK(::art::IsAlignedParam(value, alignment)) << reinterpret_cast<const void*>(value)
212
213 #define DCHECK_ALIGNED_PARAM(value, alignment) \
214 DCHECK(::art::IsAlignedParam(value, alignment)) << reinterpret_cast<const void*>(value)
215
Low16Bits(uint32_t value)216 inline uint16_t Low16Bits(uint32_t value) {
217 return static_cast<uint16_t>(value);
218 }
219
High16Bits(uint32_t value)220 inline uint16_t High16Bits(uint32_t value) {
221 return static_cast<uint16_t>(value >> 16);
222 }
223
Low32Bits(uint64_t value)224 inline uint32_t Low32Bits(uint64_t value) {
225 return static_cast<uint32_t>(value);
226 }
227
High32Bits(uint64_t value)228 inline uint32_t High32Bits(uint64_t value) {
229 return static_cast<uint32_t>(value >> 32);
230 }
231
232 // Check whether an N-bit two's-complement representation can hold value.
233 template <typename T>
IsInt(size_t N,T value)234 inline bool IsInt(size_t N, T value) {
235 if (N == BitSizeOf<T>()) {
236 return true;
237 } else {
238 CHECK_LT(0u, N);
239 CHECK_LT(N, BitSizeOf<T>());
240 T limit = static_cast<T>(1) << (N - 1u);
241 return (-limit <= value) && (value < limit);
242 }
243 }
244
245 template <typename T>
GetIntLimit(size_t bits)246 constexpr T GetIntLimit(size_t bits) {
247 DCHECK_NE(bits, 0u);
248 DCHECK_LT(bits, BitSizeOf<T>());
249 return static_cast<T>(1) << (bits - 1);
250 }
251
252 template <size_t kBits, typename T>
IsInt(T value)253 constexpr bool IsInt(T value) {
254 static_assert(kBits > 0, "kBits cannot be zero.");
255 static_assert(kBits <= BitSizeOf<T>(), "kBits must be <= max.");
256 static_assert(std::is_signed<T>::value, "Needs a signed type.");
257 // Corner case for "use all bits." Can't use the limits, as they would overflow, but it is
258 // trivially true.
259 return (kBits == BitSizeOf<T>()) ?
260 true :
261 (-GetIntLimit<T>(kBits) <= value) && (value < GetIntLimit<T>(kBits));
262 }
263
264 template <size_t kBits, typename T>
IsUint(T value)265 constexpr bool IsUint(T value) {
266 static_assert(kBits > 0, "kBits cannot be zero.");
267 static_assert(kBits <= BitSizeOf<T>(), "kBits must be <= max.");
268 static_assert(std::is_integral<T>::value, "Needs an integral type.");
269 // Corner case for "use all bits." Can't use the limits, as they would overflow, but it is
270 // trivially true.
271 // NOTE: To avoid triggering assertion in GetIntLimit(kBits+1) if kBits+1==BitSizeOf<T>(),
272 // use GetIntLimit(kBits)*2u. The unsigned arithmetic works well for us if it overflows.
273 using unsigned_type = typename std::make_unsigned<T>::type;
274 return (0 <= value) &&
275 (kBits == BitSizeOf<T>() ||
276 (static_cast<unsigned_type>(value) <= GetIntLimit<unsigned_type>(kBits) * 2u - 1u));
277 }
278
279 template <size_t kBits, typename T>
IsAbsoluteUint(T value)280 constexpr bool IsAbsoluteUint(T value) {
281 static_assert(kBits <= BitSizeOf<T>(), "kBits must be <= max.");
282 static_assert(std::is_integral<T>::value, "Needs an integral type.");
283 using unsigned_type = typename std::make_unsigned<T>::type;
284 return (kBits == BitSizeOf<T>())
285 ? true
286 : IsUint<kBits>(value < 0
287 ? static_cast<unsigned_type>(-1 - value) + 1u // Avoid overflow.
288 : static_cast<unsigned_type>(value));
289 }
290
291 // Generate maximum/minimum values for signed/unsigned n-bit integers
292 template <typename T>
MaxInt(size_t bits)293 constexpr T MaxInt(size_t bits) {
294 DCHECK(std::is_unsigned<T>::value || bits > 0u) << "bits cannot be zero for signed.";
295 DCHECK_LE(bits, BitSizeOf<T>());
296 using unsigned_type = typename std::make_unsigned<T>::type;
297 return bits == BitSizeOf<T>()
298 ? std::numeric_limits<T>::max()
299 : std::is_signed<T>::value
300 ? ((bits == 1u) ? 0 : static_cast<T>(MaxInt<unsigned_type>(bits - 1)))
301 : static_cast<T>(UINT64_C(1) << bits) - static_cast<T>(1);
302 }
303
304 template <typename T>
MinInt(size_t bits)305 constexpr T MinInt(size_t bits) {
306 DCHECK(std::is_unsigned<T>::value || bits > 0) << "bits cannot be zero for signed.";
307 DCHECK_LE(bits, BitSizeOf<T>());
308 return bits == BitSizeOf<T>()
309 ? std::numeric_limits<T>::min()
310 : std::is_signed<T>::value
311 ? ((bits == 1u) ? -1 : static_cast<T>(-1) - MaxInt<T>(bits))
312 : static_cast<T>(0);
313 }
314
315 // Using the Curiously Recurring Template Pattern to implement everything shared
316 // by LowToHighBitIterator and HighToLowBitIterator, i.e. everything but operator*().
317 template <typename T, typename Iter>
318 class BitIteratorBase
319 : public std::iterator<std::forward_iterator_tag, uint32_t, ptrdiff_t, void, void> {
320 static_assert(std::is_integral<T>::value, "T must be integral");
321 static_assert(std::is_unsigned<T>::value, "T must be unsigned");
322
323 static_assert(sizeof(T) == sizeof(uint32_t) || sizeof(T) == sizeof(uint64_t), "Unsupported size");
324
325 public:
BitIteratorBase()326 BitIteratorBase() : bits_(0u) { }
BitIteratorBase(T bits)327 explicit BitIteratorBase(T bits) : bits_(bits) { }
328
329 Iter& operator++() {
330 DCHECK_NE(bits_, 0u);
331 uint32_t bit = *static_cast<Iter&>(*this);
332 bits_ &= ~(static_cast<T>(1u) << bit);
333 return static_cast<Iter&>(*this);
334 }
335
336 Iter& operator++(int) {
337 Iter tmp(static_cast<Iter&>(*this));
338 ++*this;
339 return tmp;
340 }
341
342 protected:
343 T bits_;
344
345 template <typename U, typename I>
346 friend bool operator==(const BitIteratorBase<U, I>& lhs, const BitIteratorBase<U, I>& rhs);
347 };
348
349 template <typename T, typename Iter>
350 bool operator==(const BitIteratorBase<T, Iter>& lhs, const BitIteratorBase<T, Iter>& rhs) {
351 return lhs.bits_ == rhs.bits_;
352 }
353
354 template <typename T, typename Iter>
355 bool operator!=(const BitIteratorBase<T, Iter>& lhs, const BitIteratorBase<T, Iter>& rhs) {
356 return !(lhs == rhs);
357 }
358
359 template <typename T>
360 class LowToHighBitIterator : public BitIteratorBase<T, LowToHighBitIterator<T>> {
361 public:
362 using BitIteratorBase<T, LowToHighBitIterator<T>>::BitIteratorBase;
363
364 uint32_t operator*() const {
365 DCHECK_NE(this->bits_, 0u);
366 return CTZ(this->bits_);
367 }
368 };
369
370 template <typename T>
371 class HighToLowBitIterator : public BitIteratorBase<T, HighToLowBitIterator<T>> {
372 public:
373 using BitIteratorBase<T, HighToLowBitIterator<T>>::BitIteratorBase;
374
375 uint32_t operator*() const {
376 DCHECK_NE(this->bits_, 0u);
377 static_assert(std::numeric_limits<T>::radix == 2, "Unexpected radix!");
378 return std::numeric_limits<T>::digits - 1u - CLZ(this->bits_);
379 }
380 };
381
382 template <typename T>
LowToHighBits(T bits)383 IterationRange<LowToHighBitIterator<T>> LowToHighBits(T bits) {
384 return IterationRange<LowToHighBitIterator<T>>(
385 LowToHighBitIterator<T>(bits), LowToHighBitIterator<T>());
386 }
387
388 template <typename T>
HighToLowBits(T bits)389 IterationRange<HighToLowBitIterator<T>> HighToLowBits(T bits) {
390 return IterationRange<HighToLowBitIterator<T>>(
391 HighToLowBitIterator<T>(bits), HighToLowBitIterator<T>());
392 }
393
394 // Returns value with bit set in lowest one-bit position or 0 if 0. (java.lang.X.lowestOneBit).
395 template <typename kind>
LowestOneBitValue(kind opnd)396 inline static kind LowestOneBitValue(kind opnd) {
397 // Hacker's Delight, Section 2-1
398 return opnd & -opnd;
399 }
400
401 // Returns value with bit set in hightest one-bit position or 0 if 0. (java.lang.X.highestOneBit).
402 template <typename T>
HighestOneBitValue(T opnd)403 inline static T HighestOneBitValue(T opnd) {
404 using unsigned_type = typename std::make_unsigned<T>::type;
405 T res;
406 if (opnd == 0) {
407 res = 0;
408 } else {
409 int bit_position = BitSizeOf<T>() - (CLZ(static_cast<unsigned_type>(opnd)) + 1);
410 res = static_cast<T>(UINT64_C(1) << bit_position);
411 }
412 return res;
413 }
414
415 // Rotate bits.
416 template <typename T, bool left>
Rot(T opnd,int distance)417 inline static T Rot(T opnd, int distance) {
418 int mask = BitSizeOf<T>() - 1;
419 int unsigned_right_shift = left ? (-distance & mask) : (distance & mask);
420 int signed_left_shift = left ? (distance & mask) : (-distance & mask);
421 using unsigned_type = typename std::make_unsigned<T>::type;
422 return (static_cast<unsigned_type>(opnd) >> unsigned_right_shift) | (opnd << signed_left_shift);
423 }
424
425 // TUNING: use rbit for arm/arm64
ReverseBits32(uint32_t opnd)426 inline static uint32_t ReverseBits32(uint32_t opnd) {
427 // Hacker's Delight 7-1
428 opnd = ((opnd >> 1) & 0x55555555) | ((opnd & 0x55555555) << 1);
429 opnd = ((opnd >> 2) & 0x33333333) | ((opnd & 0x33333333) << 2);
430 opnd = ((opnd >> 4) & 0x0F0F0F0F) | ((opnd & 0x0F0F0F0F) << 4);
431 opnd = ((opnd >> 8) & 0x00FF00FF) | ((opnd & 0x00FF00FF) << 8);
432 opnd = ((opnd >> 16)) | ((opnd) << 16);
433 return opnd;
434 }
435
436 // TUNING: use rbit for arm/arm64
ReverseBits64(uint64_t opnd)437 inline static uint64_t ReverseBits64(uint64_t opnd) {
438 // Hacker's Delight 7-1
439 opnd = (opnd & 0x5555555555555555L) << 1 | ((opnd >> 1) & 0x5555555555555555L);
440 opnd = (opnd & 0x3333333333333333L) << 2 | ((opnd >> 2) & 0x3333333333333333L);
441 opnd = (opnd & 0x0f0f0f0f0f0f0f0fL) << 4 | ((opnd >> 4) & 0x0f0f0f0f0f0f0f0fL);
442 opnd = (opnd & 0x00ff00ff00ff00ffL) << 8 | ((opnd >> 8) & 0x00ff00ff00ff00ffL);
443 opnd = (opnd << 48) | ((opnd & 0xffff0000L) << 16) | ((opnd >> 16) & 0xffff0000L) | (opnd >> 48);
444 return opnd;
445 }
446
447 } // namespace art
448
449 #endif // ART_RUNTIME_BASE_BIT_UTILS_H_
450