redis中整数集合intset相关的文件为：intset.h与intset.c
intset的所有操作与操作一个排序整形数组 int a[N]类似，只是根据类型做了内存上的优化。
一、数据结构
1 typedef struct intset {2 uint32_t encoding;3 uint32_t length;4 int8_t contents[];5 } intset;intset的数据结构比较简单，使用了一个变长结构体，成员length记录当前成员数量，成员encoding记录当前的int类型，共有以下三种：
1 #define INTSET_ENC_INT16 (sizeof(int16_t))2 #define INTSET_ENC_INT32 (sizeof(int32_t))3 #define INTSET_ENC_INT64 (sizeof(int64_t))
并使用以下方法进行判断类型：
1 static uint8_t _intsetValueEncoding(int64_t v) {2 if (v < INT32_MIN || v > INT32_MAX)3 return INTSET_ENC_INT64;4 else if (v < INT16_MIN || v > INT16_MAX)5 return INTSET_ENC_INT32;6 else7 return INTSET_ENC_INT16;8 }intset是已排序好的整数集合，其大致结构如下：
1 /*2 +--------+--------+--------...--------------+3 |encoding|length |contents(encoding*length)|4 +--------+--------+--------...--------------+5 */
intset严格按照小端字节序进行存储，不论机器的字节序类型。如果是大端机器，需要进行转换，才进行存储。endianconv.h中有如下定义：
1 #if (BYTE_ORDER == LITTLE_ENDIAN) 2 #define memrev16ifbe(p) ((void)(0)) 3 #define memrev32ifbe(p) ((void)(0)) 4 #define memrev64ifbe(p) ((void)(0)) 5 #define intrev16ifbe(v) (v) 6 #define intrev32ifbe(v) (v) 7 #define intrev64ifbe(v) (v) 8 #else 9 #define memrev16ifbe(p) memrev16(p)10 #define memrev32ifbe(p) memrev32(p)11 #define memrev64ifbe(p) memrev64(p)12 #define intrev16ifbe(v) intrev16(v)13 #define intrev32ifbe(v) intrev32(v)14 #define intrev64ifbe(v) intrev64(v)15 #endif
具体实现在endianconv.c中，此处略过。
二、创建
1 intset *intsetNew(void) {2 intset *is = zmalloc(sizeof(intset));3 is->encoding = intrev32ifbe(INTSET_ENC_INT16);4 is->length = 0;5 return is;6 }刚创建好的intset是空的，默认使用最小的类型。其结构为：
1 /*此处用一根“-”表示一字节，后同2 +----+----+3 | 16| 0|4 +----+----+5 */
三、 操作
若有以下intset：
1 /*2 +----+----+--+--+--+--+--+--+--+3 | 16| 7| 1| 2| 3| 4| 5| 7| 8|4 +----+----+--+--+--+--+--+--+--+5 |contents6 7 */
现在插入一个数字6，需要调用以下方法：
1 /* Insert an integer in the intset */ 2 intset *intsetAdd(intset *is, int64_t value, uint8_t *success) { 3 uint8_t valenc = _intsetValueEncoding(value); 4 uint32_t pos; 5 if (success) *success = 1; 6 7 /* Upgrade encoding if necessary. If we need to upgrade, we know that 8 * this value should be either appended (if > 0) or prepended (if < 0), 9 * because it lies outside the range of existing values. */10 if (valenc > intrev32ifbe(is->encoding)) {11 /* This always succeeds, so we don't need to curry *success. */12 return intsetUpgradeAndAdd(is,value);13 } else {14 /* Abort if the value is already present in the set.15 * This call will populate "pos" with the right position to insert16 * the value when it cannot be found. */17 if (intsetSearch(is,value,&pos)) {18 if (success) *success = 0;19 return is;20 }21 22 is = intsetResize(is,intrev32ifbe(is->length)+1);23 if (pos < intrev32ifbe(is->length)) intsetMoveTail(is,pos,pos+1);24 }25 26 _intsetSet(is,pos,value);27 is->length = intrev32ifbe(intrev32ifbe(is->length)+1);28 return is;29 }因int16_t足以存储数字“6”，所以新插入数字的int类型与intset一致，然后需要查找插入的pos：
1 static uint8_t intsetSearch(intset *is, int64_t value, uint32_t *pos) { 2 int min = 0, max = intrev32ifbe(is->length)-1, mid = -1; 3 int64_t cur = -1; 4 5 /* The value can never be found when the set is empty */ 6 if (intrev32ifbe(is->length) == 0) { 7 if (pos) *pos = 0; 8 return 0; 9 } else {10 /* Check for the case where we know we cannot find the value,11 * but do know the insert position. */12 if (value > _intsetGet(is,max)) {13 if (pos) *pos = intrev32ifbe(is->length);14 return 0;15 } else if (value < _intsetGet(is,0)) {16 if (pos) *pos = 0;17 return 0;18 }19 }20 21 while(max >= min) {22 mid = ((unsigned int)min + (unsigned int)max) >> 1;23 cur = _intsetGet(is,mid);24 if (value > cur) {25 min = mid+1;26 } else if (value < cur) {27 max = mid-1;28 } else {29 break;30 }31 }32 33 if (value == cur) {34 if (pos) *pos = mid;35 return 1;36 } else {37 if (pos) *pos = min;38 return 0;39 }40 }因intset是已排序好的，所以使用了二分查找。过程如下
1 /* 2 find 6 3 +----+----+--+--+--+--+--+--+--+ 4 | 16| 7| 1| 2| 3| 4| 5| 7| 8| 5 +----+----+--+--+--+--+--+--+--+ 6 pos | 0| 1| 2| 3| 4| 5| 6| 7 step1 |min=0 8 |max=6 9 |mid=(0+6)>>1=310 |mid_val=411 12 pos | 0| 1| 2| 3| 4| 5| 6|13 step2 |min=414 |max=615 |mid=(4+6)>>1=516 |mid_val=717 18 pos | 0| 1| 2| 3| 4| 5| 6|19 step3 |min=420 |max=421 |mid=(4+4)>>1=522 |mid_val=523 24 pos | 0| 1| 2| 3| 4| 5| 6|25 step4 |min=526 |max=427 min>max break28 */
6在intset中不存在，查找到需要插入到pos=5的位置，此时首先要扩展intset的content：
1 static intset *intsetResize(intset *is, uint32_t len) {2 uint32_t size = len*intrev32ifbe(is->encoding);3 is = zrealloc(is,sizeof(intset)+size);4 return is;5 }扩展后：
1 /* 2 +----+----+--+--+--+--+--+--+--+--+3 | 16| 7| 1| 2| 3| 4| 5| 7| 8| |4 +----+----+--+--+--+--+--+--+--+--+5 pos | 0| 1| 2| 3| 4| 5| 6| 7|6 */
然后把原来在pos=5及之后的所有的元素向后移一格：
1 static void intsetMoveTail(intset *is, uint32_t from, uint32_t to) { 2 void *src, *dst; 3 uint32_t bytes = intrev32ifbe(is->length)-from; 4 uint32_t encoding = intrev32ifbe(is->encoding); 5 6 if (encoding == INTSET_ENC_INT64) { 7 src = (int64_t*)is->contents+from; 8 dst = (int64_t*)is->contents+to; 9 bytes *= sizeof(int64_t);10 } else if (encoding == INTSET_ENC_INT32) {11 src = (int32_t*)is->contents+from;12 dst = (int32_t*)is->contents+to;13 bytes *= sizeof(int32_t);14 } else {15 src = (int16_t*)is->contents+from;16 dst = (int16_t*)is->contents+to;17 bytes *= sizeof(int16_t);18 }19 memmove(dst,src,bytes);20 }移动后：
1 /* 2 +----+----+--+--+--+--+--+--+--+--+3 | 16| 7| 1| 2| 3| 4| 5| 7| 7| 8|4 +----+----+--+--+--+--+--+--+--+--+5 pos | 0| 1| 2| 3| 4| 5| 6| 7|6 */
其使用memmove，并不全修改未覆盖到的内存，所以此时pos=5的值 还是7
最后修改pos=5的值：
1 static void _intsetSet(intset *is, int pos, int64_t value) { 2 uint32_t encoding = intrev32ifbe(is->encoding); 3 4 if (encoding == INTSET_ENC_INT64) { 5 ((int64_t*)is->contents)[pos] = value; 6 memrev64ifbe(((int64_t*)is->contents)+pos); 7 } else if (encoding == INTSET_ENC_INT32) { 8 ((int32_t*)is->contents)[pos] = value; 9 memrev32ifbe(((int32_t*)is->contents)+pos);10 } else {11 ((int16_t*)is->contents)[pos] = value;12 memrev16ifbe(((int16_t*)is->contents)+pos);13 }14 }修改后并增加了length：
1 /* 2 +----+----+--+--+--+--+--+--+--+--+3 | 16| 8| 1| 2| 3| 4| 5| 6| 7| 8|4 +----+----+--+--+--+--+--+--+--+--+5 pos | 0| 1| 2| 3| 4| 5| 6| 7|6 */
如果此时要插入的数字是65536，超出了int16_t所能表示的范围，要先进行扩展int类型操作：
1 static intset *intsetUpgradeAndAdd(intset *is, int64_t value) { 2 uint8_t curenc = intrev32ifbe(is->encoding); 3 uint8_t newenc = _intsetValueEncoding(value); 4 int length = intrev32ifbe(is->length); 5 int prepend = value < 0 ? 1 : 0; 6 7 /* First set new encoding and resize */ 8 is->encoding = intrev32ifbe(newenc); 9 is = intsetResize(is,intrev32ifbe(is->length)+1);10 11 /* Upgrade back-to-front so we don't overwrite values.12 * Note that the "prepend" variable is used to make sure we have an empty13 * space at either the beginning or the end of the intset. */14 while(length--)15 _intsetSet(is,length+prepend,_intsetGetEncoded(is,length,curenc));16 17 /* Set the value at the beginning or the end. */18 if (prepend)19 _intsetSet(is,0,value);20 else21 _intsetSet(is,intrev32ifbe(is->length),value);22 is->length = intrev32ifbe(intrev32ifbe(is->length)+1);23 return is;24 }因其超出原来的int类型所能表示的范围，若为正数，一定是最大的，则应该插入在intset最后，否则应该在最前面。扩展完之后，从后往前将原来的数字，以新的int类型，放置在新的位置上，保证不会有未处理的数字被覆盖，处理完整。
删除操作：
1 intset *intsetRemove(intset *is, int64_t value, int *success) { 2 uint8_t valenc = _intsetValueEncoding(value); 3 uint32_t pos; 4 if (success) *success = 0; 5 6 if (valenc <= intrev32ifbe(is->encoding) && intsetSearch(is,value,&pos)) { 7 uint32_t len = intrev32ifbe(is->length); 8 9 /* We know we can delete */10 if (success) *success = 1;11 12 /* Overwrite value with tail and update length */13 if (pos < (len-1)) intsetMoveTail(is,pos+1,pos);14 is = intsetResize(is,len-1);15 is->length = intrev32ifbe(len-1);16 }17 return is;18 }找到指定元素之后，直接把后面的内存移至前面，然后resize。
redis 5.0.7 下载链接
http://download.redis.io/releases/redis-5.0.7.tar.gz
源码阅读顺序参考：
https://github.com/huangz1990/blog/blob/master/diary/2014/how-to-read-redis-source-code.rst
本文章为转载内容，我们尊重原作者对文章享有的著作权。如有内容错误或侵权问题，欢迎原作者联系我们进行内容更正或删除文章。
