Home | History | Annotate | Download | only in cutils 
      1 /*
      2  * Copyright (C) 2011 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #ifndef __CUTILS_BITOPS_H
     18 #define __CUTILS_BITOPS_H
     19 
     20 #include <stdbool.h>
     21 #include <string.h>
     22 #include <strings.h>
     23 #include <sys/cdefs.h>
     24 
     25 __BEGIN_DECLS
     26 
     27 /*
     28  * Bitmask Operations
     29  *
     30  * Note this doesn't provide any locking/exclusion, and isn't atomic.
     31  * Additionally no bounds checking is done on the bitmask array.
     32  *
     33  * Example:
     34  *
     35  * int num_resources;
     36  * unsigned int resource_bits[BITS_TO_WORDS(num_resources)];
     37  * bitmask_init(resource_bits, num_resources);
     38  * ...
     39  * int bit = bitmask_ffz(resource_bits, num_resources);
     40  * bitmask_set(resource_bits, bit);
     41  * ...
     42  * if (bitmask_test(resource_bits, bit)) { ... }
     43  * ...
     44  * bitmask_clear(resource_bits, bit);
     45  *
     46  */
     47 
     48 #define BITS_PER_WORD    (sizeof(unsigned int) * 8)
     49 #define BITS_TO_WORDS(x) (((x) + BITS_PER_WORD - 1) / BITS_PER_WORD)
     50 #define BIT_IN_WORD(x)   ((x) % BITS_PER_WORD)
     51 #define BIT_WORD(x)      ((x) / BITS_PER_WORD)
     52 #define BIT_MASK(x)      (1 << BIT_IN_WORD(x))
     53 
     54 static inline void bitmask_init(unsigned int *bitmask, int num_bits)
     55 {
     56     memset(bitmask, 0, BITS_TO_WORDS(num_bits)*sizeof(unsigned int));
     57 }
     58 
     59 static inline int bitmask_ffz(unsigned int *bitmask, int num_bits)
     60 {
     61     int bit, result;
     62     size_t i;
     63 
     64     for (i = 0; i < BITS_TO_WORDS(num_bits); i++) {
     65         bit = ffs(~bitmask[i]);
     66         if (bit) {
     67             // ffs is 1-indexed, return 0-indexed result
     68             bit--;
     69             result = BITS_PER_WORD * i + bit;
     70             if (result >= num_bits)
     71                 return -1;
     72             return result;
     73         }
     74     }
     75     return -1;
     76 }
     77 
     78 static inline int bitmask_weight(unsigned int *bitmask, int num_bits)
     79 {
     80     size_t i;
     81     int weight = 0;
     82 
     83     for (i = 0; i < BITS_TO_WORDS(num_bits); i++)
     84         weight += __builtin_popcount(bitmask[i]);
     85     return weight;
     86 }
     87 
     88 static inline void bitmask_set(unsigned int *bitmask, int bit)
     89 {
     90     bitmask[BIT_WORD(bit)] |= BIT_MASK(bit);
     91 }
     92 
     93 static inline void bitmask_clear(unsigned int *bitmask, int bit)
     94 {
     95     bitmask[BIT_WORD(bit)] &= ~BIT_MASK(bit);
     96 }
     97 
     98 static inline bool bitmask_test(unsigned int *bitmask, int bit)
     99 {
    100     return bitmask[BIT_WORD(bit)] & BIT_MASK(bit);
    101 }
    102 
    103 static inline int popcount(unsigned int x)
    104 {
    105     return __builtin_popcount(x);
    106 }
    107 
    108 static inline int popcountl(unsigned long x)
    109 {
    110     return __builtin_popcountl(x);
    111 }
    112 
    113 static inline int popcountll(unsigned long long x)
    114 {
    115     return __builtin_popcountll(x);
    116 }
    117 
    118 __END_DECLS
    119 
    120 #endif /* __CUTILS_BITOPS_H */
    121