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
typedef struct intset {
uint32_t encoding;
uint32_t length;
int8_t contents[];
} 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：
#define INTSET_ENC_INT16 (sizeof(int16_t))
#define INTSET_ENC_INT32 (sizeof(int32_t))
#define INTSET_ENC_INT64 (sizeof(int64_t))
并使用以下方法进行判断类型：
static uint8_t _intsetValueEncoding(int64_t v) {
if (v < INT32_MIN || v > INT32_MAX)
return INTSET_ENC_INT64;
else if (v < INT16_MIN || v > INT16_MAX)
return INTSET_ENC_INT32;
else
return INTSET_ENC_INT16;
}
intset是已排序好的整数集合，其大致结构如下：
/*
+--------+--------+--------...--------------+
|encoding|length |contents(encoding*length)|
+--------+--------+--------...--------------+
*/
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：
#if (BYTE_ORDER == LITTLE_ENDIAN)
#define memrev16ifbe(p) ((void)(0))
#define memrev32ifbe(p) ((void)(0))
#define memrev64ifbe(p) ((void)(0))
#define intrev16ifbe(v) (v)
#define intrev32ifbe(v) (v)
#define intrev64ifbe(v) (v)
#else
#define memrev16ifbe(p) memrev16(p)
#define memrev32ifbe(p) memrev32(p)
#define memrev64ifbe(p) memrev64(p)
#define intrev16ifbe(v) intrev16(v)
#define intrev32ifbe(v) intrev32(v)
#define intrev64ifbe(v) intrev64(v)
#endif
具体实现在endianconv.c中，此处略过。
二、创建
intset *intsetNew(void) {
intset *is = zmalloc(sizeof(intset));
is->encoding = intrev32ifbe(INTSET_ENC_INT16);
is->length = ;
return is;
}
刚创建好的intset是空的，默认使用最小的类型。其结构为：
/*此处用一根“-”表示一字节，后同
+----+----+
| 16| 0|
+----+----+
*/
三、 操作
若有以下intset：
/*
+----+----+--+--+--+--+--+--+--+
| 16| 7| 1| 2| 3| 4| 5| 7| 8|
+----+----+--+--+--+--+--+--+--+
|contents */
现在插入一个数字6，需要调用以下方法：
/* Insert an integer in the intset */
intset *intsetAdd(intset *is, int64_t value, uint8_t *success) {
uint8_t valenc = _intsetValueEncoding(value);
uint32_t pos;
if (success) *success = ; /* Upgrade encoding if necessary. If we need to upgrade, we know that
* this value should be either appended (if > 0) or prepended (if < 0),
* because it lies outside the range of existing values. */
if (valenc > intrev32ifbe(is->encoding)) {
/* This always succeeds, so we don't need to curry *success. */
return intsetUpgradeAndAdd(is,value);
} else {
/* Abort if the value is already present in the set.
* This call will populate "pos" with the right position to insert
* the value when it cannot be found. */
if (intsetSearch(is,value,&pos)) {
if (success) *success = ;
return is;
} is = intsetResize(is,intrev32ifbe(is->length)+);
if (pos < intrev32ifbe(is->length)) intsetMoveTail(is,pos,pos+);
} _intsetSet(is,pos,value);
is->length = intrev32ifbe(intrev32ifbe(is->length)+);
return is;
}
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：
static uint8_t intsetSearch(intset *is, int64_t value, uint32_t *pos) {
int min = , max = intrev32ifbe(is->length)-, mid = -;
int64_t cur = -;
/* The value can never be found when the set is empty */
if (intrev32ifbe(is->length) == ) {
if (pos) *pos = ;
return ;
} else {
/* Check for the case where we know we cannot find the value,
* but do know the insert position. */
if (value > _intsetGet(is,max)) {
if (pos) *pos = intrev32ifbe(is->length);
return ;
} else if (value < _intsetGet(is,)) {
if (pos) *pos = ;
return ;
}
}
while(max >= min) {
mid = ((unsigned int)min + (unsigned int)max) >> ;
cur = _intsetGet(is,mid);
if (value > cur) {
min = mid+;
} else if (value < cur) {
max = mid-;
} else {
break;
}
}
if (value == cur) {
if (pos) *pos = mid;
return ;
} else {
if (pos) *pos = min;
return ;
}
}
因intset是已排序好的，所以使用了二分查找。过程如下
/*
find 6
+----+----+--+--+--+--+--+--+--+
| 16| 7| 1| 2| 3| 4| 5| 7| 8|
+----+----+--+--+--+--+--+--+--+
pos | 0| 1| 2| 3| 4| 5| 6|
step1 |min=0
|max=6
|mid=(0+6)>>1=3
|mid_val=4 pos | 0| 1| 2| 3| 4| 5| 6|
step2 |min=4
|max=6
|mid=(4+6)>>1=5
|mid_val=7 pos | 0| 1| 2| 3| 4| 5| 6|
step3 |min=4
|max=4
|mid=(4+4)>>1=5
|mid_val=5 pos | 0| 1| 2| 3| 4| 5| 6|
step4 |min=5
|max=4
min>max break
*/
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：
static intset *intsetResize(intset *is, uint32_t len) {
uint32_t size = len*intrev32ifbe(is->encoding);
is = zrealloc(is,sizeof(intset)+size);
return is;
}
扩展后：
/*
+----+----+--+--+--+--+--+--+--+--+
| 16| 7| 1| 2| 3| 4| 5| 7| 8| |
+----+----+--+--+--+--+--+--+--+--+
pos | 0| 1| 2| 3| 4| 5| 6| 7|
*/
然后把原来在pos=5及之后的所有的元素向后移一格：
static void intsetMoveTail(intset *is, uint32_t from, uint32_t to) {
void *src, *dst;
uint32_t bytes = intrev32ifbe(is->length)-from;
uint32_t encoding = intrev32ifbe(is->encoding);
if (encoding == INTSET_ENC_INT64) {
src = (int64_t*)is->contents+from;
dst = (int64_t*)is->contents+to;
bytes *= sizeof(int64_t);
} else if (encoding == INTSET_ENC_INT32) {
src = (int32_t*)is->contents+from;
dst = (int32_t*)is->contents+to;
bytes *= sizeof(int32_t);
} else {
src = (int16_t*)is->contents+from;
dst = (int16_t*)is->contents+to;
bytes *= sizeof(int16_t);
}
memmove(dst,src,bytes);
}
移动后：
/*
+----+----+--+--+--+--+--+--+--+--+
| 16| 7| 1| 2| 3| 4| 5| 7| 7| 8|
+----+----+--+--+--+--+--+--+--+--+
pos | 0| 1| 2| 3| 4| 5| 6| 7|
*/
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：
static void _intsetSet(intset *is, int pos, int64_t value) {
uint32_t encoding = intrev32ifbe(is->encoding);
if (encoding == INTSET_ENC_INT64) {
((int64_t*)is->contents)[pos] = value;
memrev64ifbe(((int64_t*)is->contents)+pos);
} else if (encoding == INTSET_ENC_INT32) {
((int32_t*)is->contents)[pos] = value;
memrev32ifbe(((int32_t*)is->contents)+pos);
} else {
((int16_t*)is->contents)[pos] = value;
memrev16ifbe(((int16_t*)is->contents)+pos);
}
}
修改后并增加了length：
/*
+----+----+--+--+--+--+--+--+--+--+
| 16| 8| 1| 2| 3| 4| 5| 6| 7| 8|
+----+----+--+--+--+--+--+--+--+--+
pos | 0| 1| 2| 3| 4| 5| 6| 7|
*/
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：
static intset *intsetUpgradeAndAdd(intset *is, int64_t value) {
uint8_t curenc = intrev32ifbe(is->encoding);
uint8_t newenc = _intsetValueEncoding(value);
int length = intrev32ifbe(is->length);
int prepend = value < ? : ;
/* First set new encoding and resize */
is->encoding = intrev32ifbe(newenc);
is = intsetResize(is,intrev32ifbe(is->length)+);
/* Upgrade back-to-front so we don't overwrite values.
* Note that the "prepend" variable is used to make sure we have an empty
* space at either the beginning or the end of the intset. */
while(length--)
_intsetSet(is,length+prepend,_intsetGetEncoded(is,length,curenc));
/* Set the value at the beginning or the end. */
if (prepend)
_intsetSet(is,,value);
else
_intsetSet(is,intrev32ifbe(is->length),value);
is->length = intrev32ifbe(intrev32ifbe(is->length)+);
return is;
}
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：
intset *intsetRemove(intset *is, int64_t value, int *success) {
uint8_t valenc = _intsetValueEncoding(value);
uint32_t pos;
if (success) *success = ;
if (valenc <= intrev32ifbe(is->encoding) && intsetSearch(is,value,&pos)) {
uint32_t len = intrev32ifbe(is->length);
/* We know we can delete */
if (success) *success = ;
/* Overwrite value with tail and update length */
if (pos < (len-)) intsetMoveTail(is,pos+,pos);
is = intsetResize(is,len-);
is->length = intrev32ifbe(len-);
}
return is;
}
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