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
  22  * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
  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 <stdint.h>
  33
  34 #if defined(_MSC_VER)
  35 #include <intrin.h>
  36 #endif
  37
  38 #include "c99_compat.h"
  39
  40 #ifdef __cplusplus
  41 extern "C" {
  42 #endif
  43
  44
  45 /**
  46  * Find first bit set in word.  Least significant bit is 1.
  47  * Return 0 if no bits set.
  48  */
  49 #ifdef HAVE___BUILTIN_FFS
  50 #define ffs __builtin_ffs
  51 #elif defined(_MSC_VER) && (_M_IX86 || _M_ARM || _M_AMD64 || _M_IA64)
  52 static inline
  53 int ffs(unsigned i)
  54 {
  55    unsigned long index;
  56    if (_BitScanForward(&index, i))
  57       return index + 1;
  58    else
  59       return 0;
  60 }
  61 #else
  62 extern
  63 int ffs(unsigned i);
  64 #endif
  65
  66 #ifdef HAVE___BUILTIN_FFSLL
  67 #define ffsll __builtin_ffsll
  68 #elif defined(_MSC_VER) && (_M_AMD64 || _M_ARM || _M_IA64)
  69 static inline int
  70 ffsll(uint64_t i)
  71 {
  72    unsigned long index;
  73    if (_BitScanForward64(&index, i))
  74       return index + 1;
  75    else
  76       return 0;
  77 }
  78 #else
  79 extern int
  80 ffsll(uint64_t val);
  81 #endif
  82
  83
  84 /* Destructively loop over all of the bits in a mask as in:
  85  *
  86  * while (mymask) {
  87  *   int i = u_bit_scan(&mymask);
  88  *   ... process element i
  89  * }
  90  *
  91  */
  92 static inline int
  93 u_bit_scan(unsigned *mask)
  94 {
  95    const int i = ffs(*mask) - 1;
  96    *mask ^= (1u << i);
  97    return i;
  98 }
  99
 100 static inline int
 101 u_bit_scan64(uint64_t *mask)
 102 {
 103    const int i = ffsll(*mask) - 1;
 104    *mask ^= (((uint64_t)1) << i);
 105    return i;
 106 }
 107
 108 /* For looping over a bitmask when you want to loop over consecutive bits
 109  * manually, for example:
 110  *
 111  * while (mask) {
 112  *    int start, count, i;
 113  *
 114  *    u_bit_scan_consecutive_range(&mask, &start, &count);
 115  *
 116  *    for (i = 0; i < count; i++)
 117  *       ... process element (start+i)
 118  * }
 119  */
 120 static inline void
 121 u_bit_scan_consecutive_range(unsigned *mask, int *start, int *count)
 122 {
 123    if (*mask == 0xffffffff) {
 124       *start = 0;
 125       *count = 32;
 126       *mask = 0;
 127       return;
 128    }
 129    *start = ffs(*mask) - 1;
 130    *count = ffs(~(*mask >> *start)) - 1;
 131    *mask &= ~(((1u << *count) - 1) << *start);
 132 }
 133
 134 static inline void
 135 u_bit_scan_consecutive_range64(uint64_t *mask, int *start, int *count)
 136 {
 137    if (*mask == ~0llu) {
 138       *start = 0;
 139       *count = 64;
 140       *mask = 0;
 141       return;
 142    }
 143    *start = ffsll(*mask) - 1;
 144    *count = ffsll(~(*mask >> *start)) - 1;
 145    *mask &= ~(((((uint64_t)1) << *count) - 1) << *start);
 146 }
 147
 148
 149 #ifdef __cplusplus
 150 }
 151 #endif
 152
 153 #endif /* BITSCAN_H */