Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * pg_bitutils.h
4 : * Miscellaneous functions for bit-wise operations.
5 : *
6 : *
7 : * Copyright (c) 2019-2024, 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 1037922620 : pg_leftmost_one_pos32(uint32 word)
42 : {
43 : #ifdef HAVE__BUILTIN_CLZ
44 : Assert(word != 0);
45 :
46 1037922620 : 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 4283894 : pg_leftmost_one_pos64(uint64 word)
73 : {
74 : #ifdef HAVE__BUILTIN_CLZ
75 : Assert(word != 0);
76 :
77 : #if defined(HAVE_LONG_INT_64)
78 4283894 : return 63 - __builtin_clzl(word);
79 : #elif defined(HAVE_LONG_LONG_INT_64)
80 : return 63 - __builtin_clzll(word);
81 : #else
82 : #error must have a working 64-bit integer datatype
83 : #endif /* HAVE_LONG_INT_64 */
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 5558348 : pg_rightmost_one_pos32(uint32 word)
112 : {
113 : #ifdef HAVE__BUILTIN_CTZ
114 : Assert(word != 0);
115 :
116 5558348 : 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 15902354 : pg_rightmost_one_pos64(uint64 word)
146 : {
147 : #ifdef HAVE__BUILTIN_CTZ
148 : Assert(word != 0);
149 :
150 : #if defined(HAVE_LONG_INT_64)
151 15902354 : return __builtin_ctzl(word);
152 : #elif defined(HAVE_LONG_LONG_INT_64)
153 : return __builtin_ctzll(word);
154 : #else
155 : #error must have a working 64-bit integer datatype
156 : #endif /* HAVE_LONG_INT_64 */
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 110019572 : 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 110019572 : if ((num & (num - 1)) == 0)
199 105177884 : return num; /* already power 2 */
200 :
201 4841688 : 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 180974 : 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 180974 : if ((num & (num - 1)) == 0)
222 94284 : return num; /* already power 2 */
223 :
224 86690 : 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 570404 : pg_prevpower2_64(uint64 num)
249 : {
250 570404 : 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 724386 : pg_ceil_log2_32(uint32 num)
259 : {
260 724386 : if (num < 2)
261 0 : return 0;
262 : else
263 724386 : 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 1118264 : pg_ceil_log2_64(uint64 num)
272 : {
273 1118264 : if (num < 2)
274 462638 : return 0;
275 : else
276 655626 : return pg_leftmost_one_pos64(num - 1) + 1;
277 : }
278 :
279 : /*
280 : * With MSVC on x86_64 builds, try using native popcnt instructions via the
281 : * __popcnt and __popcnt64 intrinsics. These don't work the same as GCC's
282 : * __builtin_popcount* intrinsic functions as they always emit popcnt
283 : * instructions.
284 : */
285 : #if defined(_MSC_VER) && defined(_M_AMD64)
286 : #define HAVE_X86_64_POPCNTQ
287 : #endif
288 :
289 : /*
290 : * On x86_64, we can use the hardware popcount instruction, but only if
291 : * we can verify that the CPU supports it via the cpuid instruction.
292 : *
293 : * Otherwise, we fall back to a hand-rolled implementation.
294 : */
295 : #ifdef HAVE_X86_64_POPCNTQ
296 : #if defined(HAVE__GET_CPUID) || defined(HAVE__CPUID)
297 : #define TRY_POPCNT_FAST 1
298 : #endif
299 : #endif
300 :
301 : #ifdef TRY_POPCNT_FAST
302 : /* Attempt to use the POPCNT instruction, but perform a runtime check first */
303 : extern PGDLLIMPORT int (*pg_popcount32) (uint32 word);
304 : extern PGDLLIMPORT int (*pg_popcount64) (uint64 word);
305 : extern PGDLLIMPORT uint64 (*pg_popcount_optimized) (const char *buf, int bytes);
306 : extern PGDLLIMPORT uint64 (*pg_popcount_masked_optimized) (const char *buf, int bytes, bits8 mask);
307 :
308 : /*
309 : * We can also try to use the AVX-512 popcount instruction on some systems.
310 : * The implementation of that is located in its own file because it may
311 : * require special compiler flags that we don't want to apply to any other
312 : * files.
313 : */
314 : #ifdef USE_AVX512_POPCNT_WITH_RUNTIME_CHECK
315 : extern bool pg_popcount_avx512_available(void);
316 : extern uint64 pg_popcount_avx512(const char *buf, int bytes);
317 : extern uint64 pg_popcount_masked_avx512(const char *buf, int bytes, bits8 mask);
318 : #endif
319 :
320 : #else
321 : /* Use a portable implementation -- no need for a function pointer. */
322 : extern int pg_popcount32(uint32 word);
323 : extern int pg_popcount64(uint64 word);
324 : extern uint64 pg_popcount_optimized(const char *buf, int bytes);
325 : extern uint64 pg_popcount_masked_optimized(const char *buf, int bytes, bits8 mask);
326 :
327 : #endif /* TRY_POPCNT_FAST */
328 :
329 : /*
330 : * Returns the number of 1-bits in buf.
331 : *
332 : * If there aren't many bytes to process, the function call overhead of the
333 : * optimized versions isn't worth taking, so we inline a loop that consults
334 : * pg_number_of_ones in that case. If there are many bytes to process, we
335 : * accept the function call overhead because the optimized versions are likely
336 : * to be faster.
337 : */
338 : static inline uint64
339 10718 : pg_popcount(const char *buf, int bytes)
340 : {
341 : /*
342 : * We set the threshold to the point at which we'll first use special
343 : * instructions in the optimized version.
344 : */
345 : #if SIZEOF_VOID_P >= 8
346 10718 : int threshold = 8;
347 : #else
348 : int threshold = 4;
349 : #endif
350 :
351 10718 : if (bytes < threshold)
352 : {
353 10690 : uint64 popcnt = 0;
354 :
355 21452 : while (bytes--)
356 10762 : popcnt += pg_number_of_ones[(unsigned char) *buf++];
357 10690 : return popcnt;
358 : }
359 :
360 28 : return pg_popcount_optimized(buf, bytes);
361 : }
362 :
363 : /*
364 : * Returns the number of 1-bits in buf after applying the mask to each byte.
365 : *
366 : * Similar to pg_popcount(), we only take on the function pointer overhead when
367 : * it's likely to be faster.
368 : */
369 : static inline uint64
370 43790 : pg_popcount_masked(const char *buf, int bytes, bits8 mask)
371 : {
372 : /*
373 : * We set the threshold to the point at which we'll first use special
374 : * instructions in the optimized version.
375 : */
376 : #if SIZEOF_VOID_P >= 8
377 43790 : int threshold = 8;
378 : #else
379 : int threshold = 4;
380 : #endif
381 :
382 43790 : if (bytes < threshold)
383 : {
384 0 : uint64 popcnt = 0;
385 :
386 0 : while (bytes--)
387 0 : popcnt += pg_number_of_ones[(unsigned char) *buf++ & mask];
388 0 : return popcnt;
389 : }
390 :
391 43790 : return pg_popcount_masked_optimized(buf, bytes, mask);
392 : }
393 :
394 : /*
395 : * Rotate the bits of "word" to the right/left by n bits.
396 : */
397 : static inline uint32
398 13562602 : pg_rotate_right32(uint32 word, int n)
399 : {
400 13562602 : return (word >> n) | (word << (32 - n));
401 : }
402 :
403 : static inline uint32
404 4762260832 : pg_rotate_left32(uint32 word, int n)
405 : {
406 4762260832 : return (word << n) | (word >> (32 - n));
407 : }
408 :
409 : /* size_t variants of the above, as required */
410 :
411 : #if SIZEOF_SIZE_T == 4
412 : #define pg_leftmost_one_pos_size_t pg_leftmost_one_pos32
413 : #define pg_nextpower2_size_t pg_nextpower2_32
414 : #define pg_prevpower2_size_t pg_prevpower2_32
415 : #else
416 : #define pg_leftmost_one_pos_size_t pg_leftmost_one_pos64
417 : #define pg_nextpower2_size_t pg_nextpower2_64
418 : #define pg_prevpower2_size_t pg_prevpower2_64
419 : #endif
420 :
421 : #endif /* PG_BITUTILS_H */
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