Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * pg_bitutils.h
4 : * Miscellaneous functions for bit-wise operations.
5 : *
6 : *
7 : * Copyright (c) 2019-2026, PostgreSQL Global Development Group
8 : *
9 : * src/include/port/pg_bitutils.h
10 : *
11 : *-------------------------------------------------------------------------
12 : */
13 : #ifndef PG_BITUTILS_H
14 : #define PG_BITUTILS_H
15 :
16 : #ifdef _MSC_VER
17 : #include <intrin.h>
18 : #define HAVE_BITSCAN_FORWARD
19 : #define HAVE_BITSCAN_REVERSE
20 :
21 : #else
22 : #if defined(HAVE__BUILTIN_CTZ)
23 : #define HAVE_BITSCAN_FORWARD
24 : #endif
25 :
26 : #if defined(HAVE__BUILTIN_CLZ)
27 : #define HAVE_BITSCAN_REVERSE
28 : #endif
29 : #endif /* _MSC_VER */
30 :
31 : extern PGDLLIMPORT const uint8 pg_leftmost_one_pos[256];
32 : extern PGDLLIMPORT const uint8 pg_rightmost_one_pos[256];
33 : extern PGDLLIMPORT const uint8 pg_number_of_ones[256];
34 :
35 : /*
36 : * pg_leftmost_one_pos32
37 : * Returns the position of the most significant set bit in "word",
38 : * measured from the least significant bit. word must not be 0.
39 : */
40 : static inline int
41 713221625 : pg_leftmost_one_pos32(uint32 word)
42 : {
43 : #ifdef HAVE__BUILTIN_CLZ
44 : Assert(word != 0);
45 :
46 713221625 : return 31 - __builtin_clz(word);
47 : #elif defined(_MSC_VER)
48 : unsigned long result;
49 : bool non_zero;
50 :
51 : Assert(word != 0);
52 :
53 : non_zero = _BitScanReverse(&result, word);
54 : return (int) result;
55 : #else
56 : int shift = 32 - 8;
57 :
58 : Assert(word != 0);
59 :
60 : while ((word >> shift) == 0)
61 : shift -= 8;
62 :
63 : return shift + pg_leftmost_one_pos[(word >> shift) & 255];
64 : #endif /* HAVE__BUILTIN_CLZ */
65 : }
66 :
67 : /*
68 : * pg_leftmost_one_pos64
69 : * As above, but for a 64-bit word.
70 : */
71 : static inline int
72 2704042 : pg_leftmost_one_pos64(uint64 word)
73 : {
74 : #ifdef HAVE__BUILTIN_CLZ
75 : Assert(word != 0);
76 :
77 : #if SIZEOF_LONG == 8
78 2704042 : return 63 - __builtin_clzl(word);
79 : #elif SIZEOF_LONG_LONG == 8
80 : return 63 - __builtin_clzll(word);
81 : #else
82 : #error "cannot find integer type of the same size as uint64_t"
83 : #endif
84 :
85 : #elif defined(_MSC_VER) && (defined(_M_AMD64) || defined(_M_ARM64))
86 : unsigned long result;
87 : bool non_zero;
88 :
89 : Assert(word != 0);
90 :
91 : non_zero = _BitScanReverse64(&result, word);
92 : return (int) result;
93 : #else
94 : int shift = 64 - 8;
95 :
96 : Assert(word != 0);
97 :
98 : while ((word >> shift) == 0)
99 : shift -= 8;
100 :
101 : return shift + pg_leftmost_one_pos[(word >> shift) & 255];
102 : #endif /* HAVE__BUILTIN_CLZ */
103 : }
104 :
105 : /*
106 : * pg_rightmost_one_pos32
107 : * Returns the position of the least significant set bit in "word",
108 : * measured from the least significant bit. word must not be 0.
109 : */
110 : static inline int
111 119923858 : pg_rightmost_one_pos32(uint32 word)
112 : {
113 : #ifdef HAVE__BUILTIN_CTZ
114 : Assert(word != 0);
115 :
116 119923858 : return __builtin_ctz(word);
117 : #elif defined(_MSC_VER)
118 : unsigned long result;
119 : bool non_zero;
120 :
121 : Assert(word != 0);
122 :
123 : non_zero = _BitScanForward(&result, word);
124 : return (int) result;
125 : #else
126 : int result = 0;
127 :
128 : Assert(word != 0);
129 :
130 : while ((word & 255) == 0)
131 : {
132 : word >>= 8;
133 : result += 8;
134 : }
135 : result += pg_rightmost_one_pos[word & 255];
136 : return result;
137 : #endif /* HAVE__BUILTIN_CTZ */
138 : }
139 :
140 : /*
141 : * pg_rightmost_one_pos64
142 : * As above, but for a 64-bit word.
143 : */
144 : static inline int
145 12058386 : pg_rightmost_one_pos64(uint64 word)
146 : {
147 : #ifdef HAVE__BUILTIN_CTZ
148 : Assert(word != 0);
149 :
150 : #if SIZEOF_LONG == 8
151 12058386 : return __builtin_ctzl(word);
152 : #elif SIZEOF_LONG_LONG == 8
153 : return __builtin_ctzll(word);
154 : #else
155 : #error "cannot find integer type of the same size as uint64_t"
156 : #endif
157 :
158 : #elif defined(_MSC_VER) && (defined(_M_AMD64) || defined(_M_ARM64))
159 : unsigned long result;
160 : bool non_zero;
161 :
162 : Assert(word != 0);
163 :
164 : non_zero = _BitScanForward64(&result, word);
165 : return (int) result;
166 : #else
167 : int result = 0;
168 :
169 : Assert(word != 0);
170 :
171 : while ((word & 255) == 0)
172 : {
173 : word >>= 8;
174 : result += 8;
175 : }
176 : result += pg_rightmost_one_pos[word & 255];
177 : return result;
178 : #endif /* HAVE__BUILTIN_CTZ */
179 : }
180 :
181 : /*
182 : * pg_nextpower2_32
183 : * Returns the next higher power of 2 above 'num', or 'num' if it's
184 : * already a power of 2.
185 : *
186 : * 'num' mustn't be 0 or be above PG_UINT32_MAX / 2 + 1.
187 : */
188 : static inline uint32
189 74209206 : pg_nextpower2_32(uint32 num)
190 : {
191 : Assert(num > 0 && num <= PG_UINT32_MAX / 2 + 1);
192 :
193 : /*
194 : * A power 2 number has only 1 bit set. Subtracting 1 from such a number
195 : * will turn on all previous bits resulting in no common bits being set
196 : * between num and num-1.
197 : */
198 74209206 : if ((num & (num - 1)) == 0)
199 70136043 : return num; /* already power 2 */
200 :
201 4073163 : return ((uint32) 1) << (pg_leftmost_one_pos32(num) + 1);
202 : }
203 :
204 : /*
205 : * pg_nextpower2_64
206 : * Returns the next higher power of 2 above 'num', or 'num' if it's
207 : * already a power of 2.
208 : *
209 : * 'num' mustn't be 0 or be above PG_UINT64_MAX / 2 + 1.
210 : */
211 : static inline uint64
212 168060 : pg_nextpower2_64(uint64 num)
213 : {
214 : Assert(num > 0 && num <= PG_UINT64_MAX / 2 + 1);
215 :
216 : /*
217 : * A power 2 number has only 1 bit set. Subtracting 1 from such a number
218 : * will turn on all previous bits resulting in no common bits being set
219 : * between num and num-1.
220 : */
221 168060 : if ((num & (num - 1)) == 0)
222 86192 : return num; /* already power 2 */
223 :
224 81868 : return ((uint64) 1) << (pg_leftmost_one_pos64(num) + 1);
225 : }
226 :
227 : /*
228 : * pg_prevpower2_32
229 : * Returns the next lower power of 2 below 'num', or 'num' if it's
230 : * already a power of 2.
231 : *
232 : * 'num' mustn't be 0.
233 : */
234 : static inline uint32
235 18 : pg_prevpower2_32(uint32 num)
236 : {
237 18 : return ((uint32) 1) << pg_leftmost_one_pos32(num);
238 : }
239 :
240 : /*
241 : * pg_prevpower2_64
242 : * Returns the next lower power of 2 below 'num', or 'num' if it's
243 : * already a power of 2.
244 : *
245 : * 'num' mustn't be 0.
246 : */
247 : static inline uint64
248 559354 : pg_prevpower2_64(uint64 num)
249 : {
250 559354 : return ((uint64) 1) << pg_leftmost_one_pos64(num);
251 : }
252 :
253 : /*
254 : * pg_ceil_log2_32
255 : * Returns equivalent of ceil(log2(num))
256 : */
257 : static inline uint32
258 383168 : pg_ceil_log2_32(uint32 num)
259 : {
260 383168 : if (num < 2)
261 43 : return 0;
262 : else
263 383125 : return pg_leftmost_one_pos32(num - 1) + 1;
264 : }
265 :
266 : /*
267 : * pg_ceil_log2_64
268 : * Returns equivalent of ceil(log2(num))
269 : */
270 : static inline uint64
271 796594 : pg_ceil_log2_64(uint64 num)
272 : {
273 796594 : if (num < 2)
274 349309 : return 0;
275 : else
276 447285 : return pg_leftmost_one_pos64(num - 1) + 1;
277 : }
278 :
279 : extern uint64 pg_popcount_portable(const char *buf, int bytes);
280 : extern uint64 pg_popcount_masked_portable(const char *buf, int bytes, bits8 mask);
281 :
282 : #if defined(HAVE_X86_64_POPCNTQ) || defined(USE_SVE_POPCNT_WITH_RUNTIME_CHECK)
283 : /*
284 : * Attempt to use specialized CPU instructions, but perform a runtime check
285 : * first.
286 : */
287 : extern PGDLLIMPORT uint64 (*pg_popcount_optimized) (const char *buf, int bytes);
288 : extern PGDLLIMPORT uint64 (*pg_popcount_masked_optimized) (const char *buf, int bytes, bits8 mask);
289 :
290 : #else
291 : /* Use a portable implementation -- no need for a function pointer. */
292 : extern uint64 pg_popcount_optimized(const char *buf, int bytes);
293 : extern uint64 pg_popcount_masked_optimized(const char *buf, int bytes, bits8 mask);
294 :
295 : #endif
296 :
297 : /*
298 : * pg_popcount32
299 : * Return the number of 1 bits set in word
300 : *
301 : * Adapted from
302 : * https://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel.
303 : *
304 : * Note that newer versions of popular compilers will automatically replace
305 : * this with a special popcount instruction if possible, so we don't bother
306 : * using builtin functions or intrinsics.
307 : */
308 : static inline int
309 : pg_popcount32(uint32 word)
310 : {
311 : word -= (word >> 1) & 0x55555555;
312 : word = (word & 0x33333333) + ((word >> 2) & 0x33333333);
313 : return (((word + (word >> 4)) & 0xf0f0f0f) * 0x1010101) >> 24;
314 : }
315 :
316 : /*
317 : * pg_popcount64
318 : * Return the number of 1 bits set in word
319 : *
320 : * Adapted from
321 : * https://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel.
322 : *
323 : * Note that newer versions of popular compilers will automatically replace
324 : * this with a special popcount instruction if possible, so we don't bother
325 : * using builtin functions or intrinsics.
326 : */
327 : static inline int
328 948884 : pg_popcount64(uint64 word)
329 : {
330 948884 : word -= (word >> 1) & UINT64CONST(0x5555555555555555);
331 948884 : word = (word & UINT64CONST(0x3333333333333333)) +
332 948884 : ((word >> 2) & UINT64CONST(0x3333333333333333));
333 948884 : word = (word + (word >> 4)) & UINT64CONST(0xf0f0f0f0f0f0f0f);
334 948884 : return (word * UINT64CONST(0x101010101010101)) >> 56;
335 : }
336 :
337 : /*
338 : * Returns the number of 1-bits in buf.
339 : *
340 : * If there aren't many bytes to process, the function call overhead of the
341 : * optimized versions isn't worth taking, so we inline a loop that consults
342 : * pg_number_of_ones in that case. If there are many bytes to process, we
343 : * accept the function call overhead because the optimized versions are likely
344 : * to be faster.
345 : */
346 : static inline uint64
347 8022 : pg_popcount(const char *buf, int bytes)
348 : {
349 : /*
350 : * We set the threshold to the point at which we'll first use special
351 : * instructions in the optimized version.
352 : */
353 8022 : if (bytes < 8)
354 : {
355 7997 : uint64 popcnt = 0;
356 :
357 13380 : while (bytes--)
358 5383 : popcnt += pg_number_of_ones[(unsigned char) *buf++];
359 7997 : return popcnt;
360 : }
361 :
362 25 : return pg_popcount_optimized(buf, bytes);
363 : }
364 :
365 : /*
366 : * Returns the number of 1-bits in buf after applying the mask to each byte.
367 : *
368 : * Similar to pg_popcount(), we only take on the function pointer overhead when
369 : * it's likely to be faster.
370 : */
371 : static inline uint64
372 109437 : pg_popcount_masked(const char *buf, int bytes, bits8 mask)
373 : {
374 : /*
375 : * We set the threshold to the point at which we'll first use special
376 : * instructions in the optimized version.
377 : */
378 109437 : if (bytes < 8)
379 : {
380 0 : uint64 popcnt = 0;
381 :
382 0 : while (bytes--)
383 0 : popcnt += pg_number_of_ones[(unsigned char) *buf++ & mask];
384 0 : return popcnt;
385 : }
386 :
387 109437 : return pg_popcount_masked_optimized(buf, bytes, mask);
388 : }
389 :
390 : /*
391 : * Rotate the bits of "word" to the right/left by n bits.
392 : */
393 : static inline uint32
394 7839647 : pg_rotate_right32(uint32 word, int n)
395 : {
396 7839647 : return (word >> n) | (word << (32 - n));
397 : }
398 :
399 : static inline uint32
400 3102439842 : pg_rotate_left32(uint32 word, int n)
401 : {
402 3102439842 : return (word << n) | (word >> (32 - n));
403 : }
404 :
405 : /* size_t variants of the above, as required */
406 :
407 : #if SIZEOF_SIZE_T == 4
408 : #define pg_leftmost_one_pos_size_t pg_leftmost_one_pos32
409 : #define pg_nextpower2_size_t pg_nextpower2_32
410 : #define pg_prevpower2_size_t pg_prevpower2_32
411 : #else
412 : #define pg_leftmost_one_pos_size_t pg_leftmost_one_pos64
413 : #define pg_nextpower2_size_t pg_nextpower2_64
414 : #define pg_prevpower2_size_t pg_prevpower2_64
415 : #endif
416 :
417 : #endif /* PG_BITUTILS_H */
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