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 1274555500 : pg_leftmost_one_pos32(uint32 word)
42 : {
43 : #ifdef HAVE__BUILTIN_CLZ
44 : Assert(word != 0);
45 :
46 1274555500 : 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 5051206 : pg_leftmost_one_pos64(uint64 word)
73 : {
74 : #ifdef HAVE__BUILTIN_CLZ
75 : Assert(word != 0);
76 :
77 : #if SIZEOF_LONG == 8
78 5051206 : 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 5652524 : pg_rightmost_one_pos32(uint32 word)
112 : {
113 : #ifdef HAVE__BUILTIN_CTZ
114 : Assert(word != 0);
115 :
116 5652524 : 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 21363872 : pg_rightmost_one_pos64(uint64 word)
146 : {
147 : #ifdef HAVE__BUILTIN_CTZ
148 : Assert(word != 0);
149 :
150 : #if SIZEOF_LONG == 8
151 21363872 : 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 129113134 : 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 129113134 : if ((num & (num - 1)) == 0)
199 122655416 : return num; /* already power 2 */
200 :
201 6457718 : 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 222308 : 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 222308 : if ((num & (num - 1)) == 0)
222 114876 : return num; /* already power 2 */
223 :
224 107432 : 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 36 : pg_prevpower2_32(uint32 num)
236 : {
237 36 : 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 939060 : pg_prevpower2_64(uint64 num)
249 : {
250 939060 : 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 770502 : pg_ceil_log2_32(uint32 num)
259 : {
260 770502 : if (num < 2)
261 86 : return 0;
262 : else
263 770416 : 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 1591740 : pg_ceil_log2_64(uint64 num)
272 : {
273 1591740 : if (num < 2)
274 702052 : return 0;
275 : else
276 889688 : return pg_leftmost_one_pos64(num - 1) + 1;
277 : }
278 :
279 : extern int pg_popcount32_portable(uint32 word);
280 : extern int pg_popcount64_portable(uint64 word);
281 : extern uint64 pg_popcount_portable(const char *buf, int bytes);
282 : extern uint64 pg_popcount_masked_portable(const char *buf, int bytes, bits8 mask);
283 :
284 : #ifdef HAVE_X86_64_POPCNTQ
285 : /*
286 : * Attempt to use SSE4.2 or AVX-512 instructions, but perform a runtime check
287 : * first.
288 : */
289 : extern PGDLLIMPORT int (*pg_popcount32) (uint32 word);
290 : extern PGDLLIMPORT int (*pg_popcount64) (uint64 word);
291 : extern PGDLLIMPORT uint64 (*pg_popcount_optimized) (const char *buf, int bytes);
292 : extern PGDLLIMPORT uint64 (*pg_popcount_masked_optimized) (const char *buf, int bytes, bits8 mask);
293 :
294 : #elif defined(USE_NEON)
295 : /* Use the Neon version of pg_popcount{32,64} without function pointer. */
296 : extern int pg_popcount32(uint32 word);
297 : extern int pg_popcount64(uint64 word);
298 :
299 : /*
300 : * We can try to use an SVE-optimized pg_popcount() on some systems For that,
301 : * we do use a function pointer.
302 : */
303 : #ifdef USE_SVE_POPCNT_WITH_RUNTIME_CHECK
304 : extern PGDLLIMPORT uint64 (*pg_popcount_optimized) (const char *buf, int bytes);
305 : extern PGDLLIMPORT uint64 (*pg_popcount_masked_optimized) (const char *buf, int bytes, bits8 mask);
306 : #else
307 : extern uint64 pg_popcount_optimized(const char *buf, int bytes);
308 : extern uint64 pg_popcount_masked_optimized(const char *buf, int bytes, bits8 mask);
309 : #endif
310 :
311 : #else
312 : /* Use a portable implementation -- no need for a function pointer. */
313 : extern int pg_popcount32(uint32 word);
314 : extern int pg_popcount64(uint64 word);
315 : extern uint64 pg_popcount_optimized(const char *buf, int bytes);
316 : extern uint64 pg_popcount_masked_optimized(const char *buf, int bytes, bits8 mask);
317 :
318 : #endif
319 :
320 : /*
321 : * Returns the number of 1-bits in buf.
322 : *
323 : * If there aren't many bytes to process, the function call overhead of the
324 : * optimized versions isn't worth taking, so we inline a loop that consults
325 : * pg_number_of_ones in that case. If there are many bytes to process, we
326 : * accept the function call overhead because the optimized versions are likely
327 : * to be faster.
328 : */
329 : static inline uint64
330 10682 : pg_popcount(const char *buf, int bytes)
331 : {
332 : /*
333 : * We set the threshold to the point at which we'll first use special
334 : * instructions in the optimized version.
335 : */
336 : #if SIZEOF_VOID_P >= 8
337 10682 : int threshold = 8;
338 : #else
339 : int threshold = 4;
340 : #endif
341 :
342 10682 : if (bytes < threshold)
343 : {
344 10644 : uint64 popcnt = 0;
345 :
346 21368 : while (bytes--)
347 10724 : popcnt += pg_number_of_ones[(unsigned char) *buf++];
348 10644 : return popcnt;
349 : }
350 :
351 38 : return pg_popcount_optimized(buf, bytes);
352 : }
353 :
354 : /*
355 : * Returns the number of 1-bits in buf after applying the mask to each byte.
356 : *
357 : * Similar to pg_popcount(), we only take on the function pointer overhead when
358 : * it's likely to be faster.
359 : */
360 : static inline uint64
361 147022 : pg_popcount_masked(const char *buf, int bytes, bits8 mask)
362 : {
363 : /*
364 : * We set the threshold to the point at which we'll first use special
365 : * instructions in the optimized version.
366 : */
367 : #if SIZEOF_VOID_P >= 8
368 147022 : int threshold = 8;
369 : #else
370 : int threshold = 4;
371 : #endif
372 :
373 147022 : if (bytes < threshold)
374 : {
375 0 : uint64 popcnt = 0;
376 :
377 0 : while (bytes--)
378 0 : popcnt += pg_number_of_ones[(unsigned char) *buf++ & mask];
379 0 : return popcnt;
380 : }
381 :
382 147022 : return pg_popcount_masked_optimized(buf, bytes, mask);
383 : }
384 :
385 : /*
386 : * Rotate the bits of "word" to the right/left by n bits.
387 : */
388 : static inline uint32
389 15361538 : pg_rotate_right32(uint32 word, int n)
390 : {
391 15361538 : return (word >> n) | (word << (32 - n));
392 : }
393 :
394 : static inline uint32
395 5638215108 : pg_rotate_left32(uint32 word, int n)
396 : {
397 5638215108 : return (word << n) | (word >> (32 - n));
398 : }
399 :
400 : /* size_t variants of the above, as required */
401 :
402 : #if SIZEOF_SIZE_T == 4
403 : #define pg_leftmost_one_pos_size_t pg_leftmost_one_pos32
404 : #define pg_nextpower2_size_t pg_nextpower2_32
405 : #define pg_prevpower2_size_t pg_prevpower2_32
406 : #else
407 : #define pg_leftmost_one_pos_size_t pg_leftmost_one_pos64
408 : #define pg_nextpower2_size_t pg_nextpower2_64
409 : #define pg_prevpower2_size_t pg_prevpower2_64
410 : #endif
411 :
412 : #endif /* PG_BITUTILS_H */
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