结合redis设计与实现的redis源码学习-6-intset（整数集合）

整数集合是集合键的底层实现之一，当一个集合只包含整数值元素，并且这个结合的元素数量不多时，redis就会使用整数集合作为集合建的底层实现。它可以保存类型为int16_t,int32_t,int64_t的整数值，并且保证集合中不会出现重复元素。

整数集合具有以下特性：

1、整数集合的底层实现是数组，这个数组以有序，无重复的方式保存集合元素，在需要时，会根据新添加元素的类型来改变这个数组的类型；

2、升级操作为整数集合带来了操作上的灵活性，尽可能的节约了内存，但是不可降级；

上代码：

#ifndef __INTSET_H
#define __INTSET_H
#include <stdint.h>

typedef struct intset{
//编码方式
uint32_t encoding;
//整数集合包含的元素数量
uint32_t length;
//保存元素的数组，集合的每个元素都是contents的一个数组项，按值得大小从小到大有序排列且不重复
int8_t contents[];
}intset;

intset *intsetNew(void);
intset *intsetAdd(intset *is, int64_t value, uint8_t *success);
intset *intsetRemove(intset *is, int64_t value, int *success);
uint8_t intsetFind(intset *is, int64_t value);
int64_t intsetRandom(intset *is);
uint8_t intsetGet(intset *is, uint32_t pos, int64_t *value);
uint32_t intsetLen(intset *is);
size_t intsetBlobLen(intset *is);

#ifdef REDIS_TEST
int intsetTest(int argc, char *argv[]); //测试函数，这里我没有贴上
#endif

#endif // __INTSET_H

.c文件

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "intset.h"
#include "zmalloc.h"
#include "endianconv.h"//大小端转换的头文件

/* Note that these encodings are ordered, so:宏定义计算各类型长度
* INTSET_ENC_INT16 < INTSET_ENC_INT32 < INTSET_ENC_INT64. */
#define INTSET_ENC_INT16 (sizeof(int16_t))
#define INTSET_ENC_INT32 (sizeof(int32_t))
#define INTSET_ENC_INT64 (sizeof(int64_t))

/* 判断存储的数据大小Return the required encoding for the provided value. */
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;
}
/* Return the value at pos, given an encoding. 根据编码和位置返回数值*/
static int64_t _intsetGetEncoded(intset *is, int pos, uint8_t enc) {
int64_t v64;
int32_t v32;
int16_t v16;

if (enc == INTSET_ENC_INT64) {
memcpy(&v64,((int64_t*)is->contents)+pos,sizeof(v64));
memrev64ifbe(&v64);//这些是转换大小端的
return v64;
} else if (enc == INTSET_ENC_INT32) {
memcpy(&v32,((int32_t*)is->contents)+pos,sizeof(v32));
memrev32ifbe(&v32);
return v32;
} else {
memcpy(&v16,((int16_t*)is->contents)+pos,sizeof(v16));
memrev16ifbe(&v16);
return v16;
}
}
/* Return the value at pos, using the configured encoding. 返回排第几的数*/
static int64_t _intsetGet(intset *is, int pos) {
return _intsetGetEncoded(is,pos,intrev32ifbe(is->encoding));
}
/* Set the value at pos, using the configured encoding. 在某一位置设置值*/
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);
}
}
/* Create an empty intset. 创建一个空整数集合*/
intset *intsetNew(void) {
intset *is = zmalloc(sizeof(intset));
is->encoding = intrev32ifbe(INTSET_ENC_INT16);
is->length = 0;
return is;
}

/* Resize the intset ，重置整数集合大小*/
static intset *intsetResize(intset *is, uint32_t len) {
uint32_t size = len*intrev32ifbe(is->encoding);
is = zrealloc(is,sizeof(intset)+size);
return is;
}
/* Search for the position of "value". Return 1 when the value was found and
* sets "pos" to the position of the value within the intset. Return 0 when
* the value is not present in the intset and sets "pos" to the position
* where "value" can be inserted.寻找插入点的位置 */
static uint8_t intsetSearch(intset *is, int64_t value, uint32_t *pos) {
int min = 0, max = intrev32ifbe(is->length)-1, mid = -1;
int64_t cur = -1;

/* The value can never be found when the set is empty */
if (intrev32ifbe(is->length) == 0) {
if (pos) *pos = 0;//空集合直接返回0位
return 0;
} else {
/* Check for the case where we know we cannot find the value,
* but do know the insert position. */
if (value > _intsetGet(is,intrev32ifbe(is->length)-1)) {
if (pos) *pos = intrev32ifbe(is->length);
return 0;
} else if (value < _intsetGet(is,0)) {
if (pos) *pos = 0;
return 0;
}
}

while(max >= min) {
mid = ((unsigned int)min + (unsigned int)max) >> 1;
cur = _intsetGet(is,mid);
if (value > cur) {
min = mid+1;
} else if (value < cur) {
max = mid-1;
} else {
break;
}
}

if (value == cur) {
if (pos) *pos = mid;
return 1;
} else {
if (pos) *pos = min;
return 0;
}
}
//升级整数集合的编码大小
/* Upgrades the intset to a larger encoding and inserts the given integer. */
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 < 0 ? 1 : 0;

/* First set new encoding and resize */
is->encoding = intrev32ifbe(newenc);
is = intsetResize(is,intrev32ifbe(is->length)+1);

/* 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,0,value);
else
_intsetSet(is,intrev32ifbe(is->length),value);
is->length = intrev32ifbe(intrev32ifbe(is->length)+1);
return is;
}
//移动整数集合的数值位置
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);
//根据编码方式拷贝大小
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);
}

/* Insert an integer in the intset 将给定元素插入到整数集合中*/
intset *intsetAdd(intset *is, int64_t value, uint8_t *success) {
uint8_t valenc = _intsetValueEncoding(value);
uint32_t pos;
if (success) *success = 1;

/* 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. 升级整数集合*/
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 = 0;
return is;//如果这个元素已经存在了，那么直接返回现有集合
}

is = intsetResize(is,intrev32ifbe(is->length)+1);//增加一个元素位置
if (pos < intrev32ifbe(is->length)) intsetMoveTail(is,pos,pos+1);//移动元素
}

_intsetSet(is,pos,value);//插入位置
is->length = intrev32ifbe(intrev32ifbe(is->length)+1);
return is;
}

/* Delete integer from intset 从整数集合中移除给定元素*/
intset *intsetRemove(intset *is, int64_t value, int *success) {
uint8_t valenc = _intsetValueEncoding(value);
uint32_t pos;
if (success) *success = 0;

if (valenc <= intrev32ifbe(is->encoding) && intsetSearch(is,value,&pos)) {
uint32_t len = intrev32ifbe(is->length);

/* We know we can delete */
if (success) *success = 1;

/* Overwrite value with tail and update length */
if (pos < (len-1)) intsetMoveTail(is,pos+1,pos);//移动元素
is = intsetResize(is,len-1);
is->length = intrev32ifbe(len-1);
}
return is;
}
/* Determine whether a value belongs to this set 检查给定值是否存在于集合中 */
uint8_t intsetFind(intset *is, int64_t value) {
uint8_t valenc = _intsetValueEncoding(value);
return valenc <= intrev32ifbe(is->encoding) && intsetSearch(is,value,NULL);
}

/* Return random member 随机返回集合中的一个值*/
int64_t intsetRandom(intset *is) {
return _intsetGet(is,rand()%intrev32ifbe(is->length));
}

/* Sets the value to the value at the given position. When this position is
* out of range the function returns 0, when in range it returns 1.
* 取出底层数组在给定索引上的元素*/
uint8_t intsetGet(intset *is, uint32_t pos, int64_t *value) {
if (pos < intrev32ifbe(is->length)) {
*value = _intsetGet(is,pos);
return 1;
}
return 0;
}

/* Return intset length 返回整数集合包含的元素个数 */
uint32_t intsetLen(intset *is) {
return intrev32ifbe(is->length);
}

/* Return intset blob size in bytes. 返回整数集合所占用的内存字节数 */
size_t intsetBlobLen(intset *is) {
return sizeof(intset)+intrev32ifbe(is->length)*intrev32ifbe(is->encoding);
}
//还有一些测试函数，在此不表