intset 实现了一个数字元素的集合。

使用数组和元素的有序存放实现存取，查找过程使用二分查找法，所有插入删除的的效率为O(log2N)。 与其他数据结构类似，作者使用变编码方式实现对内存的高效利用。 初始化的intset中的数字定义为int16_t，即每个元素占用2个字节，而随着数据的插入，逐渐调整编码方式到int32_t或int64_t

 

上代码

intset.h

1 #ifndef __INTSET_H 2 #define __INTSET_H 3 #include 
     
       4  5 typedef struct intset { 6     uint32_t encoding; 7     uint32_t length; 8     int8_t contents[]; 9 } intset;10 11 intset *intsetNew(void);12 intset *intsetAdd(intset *is, int64_t value, uint8_t *success);13 intset *intsetRemove(intset *is, int64_t value, int *success);14 uint8_t intsetFind(intset *is, int64_t value);15 int64_t intsetRandom(intset *is);16 uint8_t intsetGet(intset *is, uint32_t pos, int64_t *value);17 uint32_t intsetLen(intset *is);18 19 #endif // __INTSET_H
     

intset.c

1 #include 
     
        2 #include 
      
         3 #include 
       
          4 #include "intset.h"  5 #include "zmalloc.h"  6   7 /* Note that these encodings are ordered, so:  8  * INTSET_ENC_INT16 < INTSET_ENC_INT32 < INTSET_ENC_INT64. */  9 #define INTSET_ENC_INT16 (sizeof(int16_t))  10 #define INTSET_ENC_INT32 (sizeof(int32_t)) 11 #define INTSET_ENC_INT64 (sizeof(int64_t)) 12  13 /* Return the required encoding for the provided value. */ 14 //根据v的值判断使用哪儿种int以节省内存 15 static uint8_t _intsetValueEncoding(int64_t v) { 16     if (v < INT32_MIN || v > INT32_MAX) 17         return INTSET_ENC_INT64; 18     else if (v < INT16_MIN || v > INT16_MAX) 19         return INTSET_ENC_INT32; 20     return INTSET_ENC_INT16; 21 } 22  23 //得到enc编码方式下的第pos个位置的值 24 /* Return the value at pos, given an encoding. */ 25 static int64_t _intsetGetEncoded(intset *is, int pos, uint8_t enc) { 26     if (enc == INTSET_ENC_INT64) 27         return ((int64_t*)is->contents)[pos]; 28     else if (enc == INTSET_ENC_INT32) 29         return ((int32_t*)is->contents)[pos]; 30     return ((int16_t*)is->contents)[pos]; 31 } 32  33 //得到is中第pos个位置的value 34 /* Return the value at pos, using the configured encoding. */ 35 static int64_t _intsetGet(intset *is, int pos) { 36     return _intsetGetEncoded(is,pos,is->encoding); 37 } 38  39 //在第n个pos个位置存放value 40 /* Set the value at pos, using the configured encoding. */ 41 static void _intsetSet(intset *is, int pos, int64_t value) { 42     if (is->encoding == INTSET_ENC_INT64) 43         ((int64_t*)is->contents)[pos] = value; 44     else if (is->encoding == INTSET_ENC_INT32) 45         ((int32_t*)is->contents)[pos] = value; 46     else 47         ((int16_t*)is->contents)[pos] = value; 48 } 49  50 //得到一个新的intset，编码采用INTSET_ENC_INT16 51 /* Create an empty intset. */ 52 intset *intsetNew(void) { 53     intset *is = zmalloc(sizeof(intset)); 54     is->encoding = INTSET_ENC_INT16; 55     is->length = 0; 56     return is; 57 } 58  59 /* Resize the intset */ 60 //重新为intset分配内存 61 static intset *intsetResize(intset *is, uint32_t len) { 62     uint32_t size = len*is->encoding; 63     is = zrealloc(is,sizeof(intset)+size); 64     return is; 65 } 66  67  68 //在排好序的iniset中查找value 69 //如果找到，返回1，*pos为其所在位置 70 //如果找不到，返回0，*pos为其能插入的位置 71 //二分查找法 72 /* Search for the position of "value". Return 1 when the value was found and 73  * sets "pos" to the position of the value within the intset. Return 0 when 74  * the value is not present in the intset and sets "pos" to the position 75  * where "value" can be inserted. */ 76 static uint8_t intsetSearch(intset *is, int64_t value, uint32_t *pos) { 77     int min = 0, max = is->length-1, mid = -1; 78     int64_t cur = -1; 79  80     /* The value can never be found when the set is empty */ 81     if (is->length == 0) { 82         if (pos) *pos = 0; 83         return 0; 84     } else { 85         /* Check for the case where we know we cannot find the value, 86          * but do know the insert position. */ 87         //如果插入值大于最后一个元素，或者小于第一个元素，则可以认定无法找到该元素 88         if (value > _intsetGet(is,is->length-1)) { 89             if (pos) *pos = is->length; 90             return 0; 91         } else if (value < _intsetGet(is,0)) { 92             if (pos) *pos = 0; 93             return 0; 94         } 95     } 96  97     while(max >= min) { 98         mid = (min+max)/2; 99         cur = _intsetGet(is,mid);100         if (value > cur) {101             min = mid+1;102         } else if (value < cur) {103             max = mid-1;104         } else {105             break;106         }107     }108 109     if (value == cur) {110         if (pos) *pos = mid;111         return 1;112     } else {113         if (pos) *pos = min;114         return 0;115     }116 }117 118 //升级intset的编码，并且出入一个新数字，因为新数字的绝对值一定大于119 //当前intset中所有的数字的绝对值，如果是负数，则最小，放在最前边，否则放在最后边120 /* Upgrades the intset to a larger encoding and inserts the given integer. */121 static intset *intsetUpgradeAndAdd(intset *is, int64_t value) {122     uint8_t curenc = is->encoding;123     uint8_t newenc = _intsetValueEncoding(value);124     int length = is->length;125     int prepend = value < 0 ? 1 : 0;126 127     /* First set new encoding and resize */128     is->encoding = newenc;129     is = intsetResize(is,is->length+1);130 131     /* Upgrade back-to-front so we don't overwrite values.132      * Note that the "prepend" variable is used to make sure we have an empty133      * space at either the beginning or the end of the intset. */134     while(length--)135         _intsetSet(is,length+prepend,_intsetGetEncoded(is,length,curenc));136 137     /* Set the value at the beginning or the end. */138     if (prepend)139         _intsetSet(is,0,value);140     else141         _intsetSet(is,is->length,value);142     is->length++;143     return is;144 }145 146 //把from开始直到最后intset最后的内容move到to开始的地方，在这之前，应该要resize一下147 static void intsetMoveTail(intset *is, uint32_t from, uint32_t to) {148     void *src, *dst;149     uint32_t bytes = is->length-from;150     if (is->encoding == INTSET_ENC_INT64) {151         src = (int64_t*)is->contents+from;152         dst = (int64_t*)is->contents+to;153         bytes *= sizeof(int64_t);154     } else if (is->encoding == INTSET_ENC_INT32) {155         src = (int32_t*)is->contents+from;156         dst = (int32_t*)is->contents+to;157         bytes *= sizeof(int32_t);158     } else {159         src = (int16_t*)is->contents+from;160         dst = (int16_t*)is->contents+to;161         bytes *= sizeof(int16_t);162     }163     memmove(dst,src,bytes);164 }165 166 //在intset中插入一个元素，如果返回0，表示已经存在，否则返回1167 /* Insert an integer in the intset */168 intset *intsetAdd(intset *is, int64_t value, uint8_t *success) {169     uint8_t valenc = _intsetValueEncoding(value);170     uint32_t pos;171     if (success) *success = 1;172 173     /* Upgrade encoding if necessary. If we need to upgrade, we know that174      * this value should be either appended (if > 0) or prepended (if < 0),175      * because it lies outside the range of existing values. */176     if (valenc > is->encoding) {177         /* This always succeeds, so we don't need to curry *success. */178         return intsetUpgradeAndAdd(is,value);179     } else {180         /* Abort if the value is already present in the set.181          * This call will populate "pos" with the right position to insert182          * the value when it cannot be found. */183         if (intsetSearch(is,value,&pos)) {184             if (success) *success = 0;185             return is;186         }187 188         is = intsetResize(is,is->length+1);189         if (pos < is->length) intsetMoveTail(is,pos,pos+1);190     }191 192     _intsetSet(is,pos,value);193     is->length++;194     return is;195 }196 197 //在intset中删除一个元素value198 /* Delete integer from intset */199 intset *intsetRemove(intset *is, int64_t value, int *success) {200     uint8_t valenc = _intsetValueEncoding(value);201     uint32_t pos;202     if (success) *success = 0;203 204     if (valenc <= is->encoding && intsetSearch(is,value,&pos)) {205         /* We know we can delete */206         if (success) *success = 1;207 208         /* Overwrite value with tail and update length */209         if (pos < (is->length-1)) intsetMoveTail(is,pos+1,pos);210         is = intsetResize(is,is->length-1);211         is->length--;212     }213     return is;214 }215 216 //判断value是否在is中217 /* Determine whether a value belongs to this set */218 uint8_t intsetFind(intset *is, int64_t value) {219     uint8_t valenc = _intsetValueEncoding(value);220     return valenc <= is->encoding && intsetSearch(is,value,NULL);221 }222 223 //随机取一个intset中的元素224 /* Return random member */225 int64_t intsetRandom(intset *is) {226     return _intsetGet(is,rand()%is->length);227 }228 229 //把pos位置上的元素取出，如果超出位置，返回0，找到了则返回1，*value为其值230 /* Sets the value to the value at the given position. When this position is231  * out of range the function returns 0, when in range it returns 1. */232 uint8_t intsetGet(intset *is, uint32_t pos, int64_t *value) {233     if (pos < is->length) {234         *value = _intsetGet(is,pos);235         return 1;236     }237     return 0;238 }239 240 //得到intset的元素数量241 /* Return intset length */242 uint32_t intsetLen(intset *is) {243     return is->length;244 }245 246 #ifdef INTSET_TEST_MAIN247 #include 
        
         248 249 void intsetRepr(intset *is) {250     int i;251     for (i = 0; i < is->length; i++) {252         printf("%lld\n", (uint64_t)_intsetGet(is,i));253     }254     printf("\n");255 }256 257 void error(char *err) {258     printf("%s\n", err);259     exit(1);260 }261 262 void ok(void) {263     printf("OK\n");264 }265 266 long long usec(void) {267     struct timeval tv;268     gettimeofday(&tv,NULL);269     return (((long long)tv.tv_sec)*1000000)+tv.tv_usec;270 }271 272 #define assert(_e) ((_e)?(void)0:(_assert(#_e,__FILE__,__LINE__),exit(1)))273 void _assert(char *estr, char *file, int line) {274     printf("\n\n=== ASSERTION FAILED ===\n");275     printf("==> %s:%d '%s' is not true\n",file,line,estr);276 }277 278 intset *createSet(int bits, int size) {279     uint64_t mask = (1<
         
           32) {285             value = (rand()*rand()) & mask;286         } else {287             value = rand() & mask;288         }289         is = intsetAdd(is,value,NULL);290     }291     return is;292 }293 294 void checkConsistency(intset *is) {295     int i;296 297     for (i = 0; i < (is->length-1); i++) {298         if (is->encoding == INTSET_ENC_INT16) {299             int16_t *i16 = (int16_t*)is->contents;300             assert(i16[i] < i16[i+1]);301         } else if (is->encoding == INTSET_ENC_INT32) {302             int32_t *i32 = (int32_t*)is->contents;303             assert(i32[i] < i32[i+1]);304         } else {305             int64_t *i64 = (int64_t*)is->contents;306             assert(i64[i] < i64[i+1]);307         }308     }309 }310 311 int main(int argc, char **argv) {312     uint8_t success;313     int i;314     intset *is;315     sranddev();316 317     printf("Value encodings: "); {318         assert(_intsetValueEncoding(-32768) == INTSET_ENC_INT16);319         assert(_intsetValueEncoding(+32767) == INTSET_ENC_INT16);320         assert(_intsetValueEncoding(-32769) == INTSET_ENC_INT32);321         assert(_intsetValueEncoding(+32768) == INTSET_ENC_INT32);322         assert(_intsetValueEncoding(-2147483648) == INTSET_ENC_INT32);323         assert(_intsetValueEncoding(+2147483647) == INTSET_ENC_INT32);324         assert(_intsetValueEncoding(-2147483649) == INTSET_ENC_INT64);325         assert(_intsetValueEncoding(+2147483648) == INTSET_ENC_INT64);326         assert(_intsetValueEncoding(-9223372036854775808ull) == INTSET_ENC_INT64);327         assert(_intsetValueEncoding(+9223372036854775807ull) == INTSET_ENC_INT64);328         ok();329     }330 331     printf("Basic adding: "); {332         is = intsetNew();333         is = intsetAdd(is,5,&success); assert(success);334         is = intsetAdd(is,6,&success); assert(success);335         is = intsetAdd(is,4,&success); assert(success);336         is = intsetAdd(is,4,&success); assert(!success);337         ok();338     }339 340     printf("Large number of random adds: "); {341         int inserts = 0;342         is = intsetNew();343         for (i = 0; i < 1024; i++) {344             is = intsetAdd(is,rand()%0x800,&success);345             if (success) inserts++;346         }347         assert(is->length == inserts);348         checkConsistency(is);349         ok();350     }351 352     printf("Upgrade from int16 to int32: "); {353         is = intsetNew();354         is = intsetAdd(is,32,NULL);355         assert(is->encoding == INTSET_ENC_INT16);356         is = intsetAdd(is,65535,NULL);357         assert(is->encoding == INTSET_ENC_INT32);358         assert(intsetFind(is,32));359         assert(intsetFind(is,65535));360         checkConsistency(is);361 362         is = intsetNew();363         is = intsetAdd(is,32,NULL);364         assert(is->encoding == INTSET_ENC_INT16);365         is = intsetAdd(is,-65535,NULL);366         assert(is->encoding == INTSET_ENC_INT32);367         assert(intsetFind(is,32));368         assert(intsetFind(is,-65535));369         checkConsistency(is);370         ok();371     }372 373     printf("Upgrade from int16 to int64: "); {374         is = intsetNew();375         is = intsetAdd(is,32,NULL);376         assert(is->encoding == INTSET_ENC_INT16);377         is = intsetAdd(is,4294967295,NULL);378         assert(is->encoding == INTSET_ENC_INT64);379         assert(intsetFind(is,32));380         assert(intsetFind(is,4294967295));381         checkConsistency(is);382 383         is = intsetNew();384         is = intsetAdd(is,32,NULL);385         assert(is->encoding == INTSET_ENC_INT16);386         is = intsetAdd(is,-4294967295,NULL);387         assert(is->encoding == INTSET_ENC_INT64);388         assert(intsetFind(is,32));389         assert(intsetFind(is,-4294967295));390         checkConsistency(is);391         ok();392     }393 394     printf("Upgrade from int32 to int64: "); {395         is = intsetNew();396         is = intsetAdd(is,65535,NULL);397         assert(is->encoding == INTSET_ENC_INT32);398         is = intsetAdd(is,4294967295,NULL);399         assert(is->encoding == INTSET_ENC_INT64);400         assert(intsetFind(is,65535));401         assert(intsetFind(is,4294967295));402         checkConsistency(is);403 404         is = intsetNew();405         is = intsetAdd(is,65535,NULL);406         assert(is->encoding == INTSET_ENC_INT32);407         is = intsetAdd(is,-4294967295,NULL);408         assert(is->encoding == INTSET_ENC_INT64);409         assert(intsetFind(is,65535));410         assert(intsetFind(is,-4294967295));411         checkConsistency(is);412         ok();413     }414 415     printf("Stress lookups: "); {416         long num = 100000, size = 10000;417         int i, bits = 20;418         long long start;419         is = createSet(bits,size);420         checkConsistency(is);421 422         start = usec();423         for (i = 0; i < num; i++) intsetSearch(is,rand() % ((1<