src/util/bitscan.h

   1 /**************************************************************************
   2  *
   3  * Copyright 2008 VMware, Inc.
   4  * All Rights Reserved.
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a
   7  * copy of this software and associated documentation files (the
   8  * "Software"), to deal in the Software without restriction, including
   9  * without limitation the rights to use, copy, modify, merge, publish,
  10  * distribute, sub license, and/or sell copies of the Software, and to
  11  * permit persons to whom the Software is furnished to do so, subject to
  12  * the following conditions:
  13  *
  14  * The above copyright notice and this permission notice (including the
  15  * next paragraph) shall be included in all copies or substantial portions
  16  * of the Software.
  17  *
  18  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  19  * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  20  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.
  21  * IN NO EVENT SHALL VMWARE AND/OR ITS SUPPLIERS BE LIABLE FOR
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  23  * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
  24  * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  25  *
  26  **************************************************************************/
  27
  28
  29 #ifndef BITSCAN_H
  30 #define BITSCAN_H
  31
  32 #include <assert.h>
  33 #include <stdint.h>
  34 #include <stdbool.h>
  35 #include <string.h>
  36
  37 #if defined(_MSC_VER)
  38 #include <intrin.h>
  39 #endif
  40
  41 #if defined(__POPCNT__)
  42 #include <popcntintrin.h>
  43 #endif
  44
  45 #include "c99_compat.h"
  46
  47 #ifdef __cplusplus
  48 extern "C" {
  49 #endif
  50
  51
  52 /**
  53  * Find first bit set in word.  Least significant bit is 1.
  54  * Return 0 if no bits set.
  55  */
  56 #ifdef HAVE___BUILTIN_FFS
  57 #define ffs __builtin_ffs
  58 #elif defined(_MSC_VER) && (_M_IX86 || _M_ARM || _M_AMD64 || _M_IA64)
  59 static inline
  60 int ffs(int i)
  61 {
  62    unsigned long index;
  63    if (_BitScanForward(&index, i))
  64       return index + 1;
  65    else
  66       return 0;
  67 }
  68 #else
  69 extern
  70 int ffs(int i);
  71 #endif
  72
  73 #ifdef HAVE___BUILTIN_FFSLL
  74 #define ffsll __builtin_ffsll
  75 #elif defined(_MSC_VER) && (_M_AMD64 || _M_ARM64 || _M_IA64)
  76 static inline int
  77 ffsll(long long int i)
  78 {
  79    unsigned long index;
  80    if (_BitScanForward64(&index, i))
  81       return index + 1;
  82    else
  83       return 0;
  84 }
  85 #else
  86 extern int
  87 ffsll(long long int val);
  88 #endif
  89
  90
  91 /* Destructively loop over all of the bits in a mask as in:
  92  *
  93  * while (mymask) {
  94  *   int i = u_bit_scan(&mymask);
  95  *   ... process element i
  96  * }
  97  *
  98  */
  99 static inline int
 100 u_bit_scan(unsigned *mask)
 101 {
 102    const int i = ffs(*mask) - 1;
 103    *mask ^= (1u << i);
 104    return i;
 105 }
 106
 107 static inline int
 108 u_bit_scan64(uint64_t *mask)
 109 {
 110    const int i = ffsll(*mask) - 1;
 111    *mask ^= (((uint64_t)1) << i);
 112    return i;
 113 }
 114
 115 /* Determine if an unsigned value is a power of two.
 116  *
 117  * \note
 118  * Zero is treated as a power of two.
 119  */
 120 static inline bool
 121 util_is_power_of_two_or_zero(unsigned v)
 122 {
 123    return (v & (v - 1)) == 0;
 124 }
 125
 126 /* Determine if an uint64_t value is a power of two.
 127  *
 128  * \note
 129  * Zero is treated as a power of two.
 130  */
 131 static inline bool
 132 util_is_power_of_two_or_zero64(uint64_t v)
 133 {
 134    return (v & (v - 1)) == 0;
 135 }
 136
 137 /* Determine if an unsigned value is a power of two.
 138  *
 139  * \note
 140  * Zero is \b not treated as a power of two.
 141  */
 142 static inline bool
 143 util_is_power_of_two_nonzero(unsigned v)
 144 {
 145    /* __POPCNT__ is different from HAVE___BUILTIN_POPCOUNT.  The latter
 146     * indicates the existence of the __builtin_popcount function.  The former
 147     * indicates that _mm_popcnt_u32 exists and is a native instruction.
 148     *
 149     * The other alternative is to use SSE 4.2 compile-time flags.  This has
 150     * two drawbacks.  First, there is currently no build infrastructure for
 151     * SSE 4.2 (only 4.1), so that would have to be added.  Second, some AMD
 152     * CPUs support POPCNT but not SSE 4.2 (e.g., Barcelona).
 153     */
 154 #ifdef __POPCNT__
 155    return _mm_popcnt_u32(v) == 1;
 156 #else
 157    return v != 0 && (v & (v - 1)) == 0;
 158 #endif
 159 }
 160
 161 /* For looping over a bitmask when you want to loop over consecutive bits
 162  * manually, for example:
 163  *
 164  * while (mask) {
 165  *    int start, count, i;
 166  *
 167  *    u_bit_scan_consecutive_range(&mask, &start, &count);
 168  *
 169  *    for (i = 0; i < count; i++)
 170  *       ... process element (start+i)
 171  * }
 172  */
 173 static inline void
 174 u_bit_scan_consecutive_range(unsigned *mask, int *start, int *count)
 175 {
 176    if (*mask == 0xffffffff) {
 177       *start = 0;
 178       *count = 32;
 179       *mask = 0;
 180       return;
 181    }
 182    *start = ffs(*mask) - 1;
 183    *count = ffs(~(*mask >> *start)) - 1;
 184    *mask &= ~(((1u << *count) - 1) << *start);
 185 }
 186
 187 static inline void
 188 u_bit_scan_consecutive_range64(uint64_t *mask, int *start, int *count)
 189 {
 190    if (*mask == ~0ull) {
 191       *start = 0;
 192       *count = 64;
 193       *mask = 0;
 194       return;
 195    }
 196    *start = ffsll(*mask) - 1;
 197    *count = ffsll(~(*mask >> *start)) - 1;
 198    *mask &= ~(((((uint64_t)1) << *count) - 1) << *start);
 199 }
 200
 201
 202 /**
 203  * Find last bit set in a word.  The least significant bit is 1.
 204  * Return 0 if no bits are set.
 205  * Essentially ffs() in the reverse direction.
 206  */
 207 static inline unsigned
 208 util_last_bit(unsigned u)
 209 {
 210 #if defined(HAVE___BUILTIN_CLZ)
 211    return u == 0 ? 0 : 32 - __builtin_clz(u);
 212 #elif defined(_MSC_VER) && (_M_IX86 || _M_ARM || _M_AMD64 || _M_IA64)
 213    unsigned long index;
 214    if (_BitScanReverse(&index, u))
 215       return index + 1;
 216    else
 217       return 0;
 218 #else
 219    unsigned r = 0;
 220    while (u) {
 221       r++;
 222       u >>= 1;
 223    }
 224    return r;
 225 #endif
 226 }
 227
 228 /**
 229  * Find last bit set in a word.  The least significant bit is 1.
 230  * Return 0 if no bits are set.
 231  * Essentially ffsll() in the reverse direction.
 232  */
 233 static inline unsigned
 234 util_last_bit64(uint64_t u)
 235 {
 236 #if defined(HAVE___BUILTIN_CLZLL)
 237    return u == 0 ? 0 : 64 - __builtin_clzll(u);
 238 #elif defined(_MSC_VER) && (_M_AMD64 || _M_ARM64 || _M_IA64)
 239    unsigned long index;
 240    if (_BitScanReverse64(&index, u))
 241       return index + 1;
 242    else
 243       return 0;
 244 #else
 245    unsigned r = 0;
 246    while (u) {
 247       r++;
 248       u >>= 1;
 249    }
 250    return r;
 251 #endif
 252 }
 253
 254 /**
 255  * Find last bit in a word that does not match the sign bit. The least
 256  * significant bit is 1.
 257  * Return 0 if no bits are set.
 258  */
 259 static inline unsigned
 260 util_last_bit_signed(int i)
 261 {
 262    if (i >= 0)
 263       return util_last_bit(i);
 264    else
 265       return util_last_bit(~(unsigned)i);
 266 }
 267
 268 /* Returns a bitfield in which the first count bits starting at start are
 269  * set.
 270  */
 271 static inline unsigned
 272 u_bit_consecutive(unsigned start, unsigned count)
 273 {
 274    assert(start + count <= 32);
 275    if (count == 32)
 276       return ~0;
 277    return ((1u << count) - 1) << start;
 278 }
 279
 280 static inline uint64_t
 281 u_bit_consecutive64(unsigned start, unsigned count)
 282 {
 283    assert(start + count <= 64);
 284    if (count == 64)
 285       return ~(uint64_t)0;
 286    return (((uint64_t)1 << count) - 1) << start;
 287 }
 288
 289 /**
 290  * Return number of bits set in n.
 291  */
 292 static inline unsigned
 293 util_bitcount(unsigned n)
 294 {
 295 #if defined(HAVE___BUILTIN_POPCOUNT)
 296    return __builtin_popcount(n);
 297 #else
 298    /* K&R classic bitcount.
 299     *
 300     * For each iteration, clear the LSB from the bitfield.
 301     * Requires only one iteration per set bit, instead of
 302     * one iteration per bit less than highest set bit.
 303     */
 304    unsigned bits;
 305    for (bits = 0; n; bits++) {
 306       n &= n - 1;
 307    }
 308    return bits;
 309 #endif
 310 }
 311
 312 static inline unsigned
 313 util_bitcount64(uint64_t n)
 314 {
 315 #ifdef HAVE___BUILTIN_POPCOUNTLL
 316    return __builtin_popcountll(n);
 317 #else
 318    return util_bitcount(n) + util_bitcount(n >> 32);
 319 #endif
 320 }
 321
 322 #ifdef __cplusplus
 323 }
 324 #endif
 325
 326 #endif /* BITSCAN_H */