redis之intset

今天来学习一下redis里面的整数集合。

typedef struct intset {  //结构体大小为8uint32_t encoding;  //编码方式uint32_t length;  //数组长度int8_t contents[];  //数组下表从0开始
} intset;

encoding是contents数组元素的编码方式，contents里面存储整数。

/** Copyright (c) 2009-2012, Pieter Noordhuis <pcnoordhuis at gmail dot com>* Copyright (c) 2009-2012, Salvatore Sanfilippo <antirez at gmail dot com>* All rights reserved.** Redistribution and use in source and binary forms, with or without* modification, are permitted provided that the following conditions are met:**   * Redistributions of source code must retain the above copyright notice,*     this list of conditions and the following disclaimer.*   * Redistributions in binary form must reproduce the above copyright*     notice, this list of conditions and the following disclaimer in the*     documentation and/or other materials provided with the distribution.*   * Neither the name of Redis nor the names of its contributors may be used*     to endorse or promote products derived from this software without*     specific prior written permission.** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE* POSSIBILITY OF SUCH DAMAGE.*/#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "intset.h"
#include "zmalloc.h"
#include "endianconv.h"/* Note that these encodings are ordered, so:* INTSET_ENC_INT16 < INTSET_ENC_INT32 < INTSET_ENC_INT64. */
#define INTSET_ENC_INT16 (sizeof(int16_t))  //2
#define INTSET_ENC_INT32 (sizeof(int32_t))  //4
#define INTSET_ENC_INT64 (sizeof(int64_t))  //8/* Return the required encoding for the provided value. */
static uint8_t _intsetValueEncoding(int64_t v) {//返回适用于传入值v的编码方式if (v < INT32_MIN || v > INT32_MAX)return INTSET_ENC_INT64;else if (v < INT16_MIN || v > INT16_MAX)return INTSET_ENC_INT32;elsereturn INTSET_ENC_INT16;
}/* Return the value at pos, given an encoding. */
//根据给定的编码方式enc,返回集合的底层数组在pos索引上的元素
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);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. */
static int64_t _intsetGet(intset *is, int pos) {//根据集合的编码方式，返回底层数组在 pos 索引上的值return _intsetGetEncoded(is,pos,intrev32ifbe(is->encoding));
}/* Set the value at pos, using the configured encoding. */
static void _intsetSet(intset *is, int pos, int64_t value) {//根据集合的编码方式，将底层数组在 pos 位置上的值设为 valueuint32_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. */
intset *intsetNew(void) {//创建并返回一个新的空整数集合intset *is = zmalloc(sizeof(intset));is->encoding = intrev32ifbe(INTSET_ENC_INT16); //存储字节序转换is->length = 0;return is;
}/* Resize the intset */
static intset *intsetResize(intset *is, uint32_t len) {//调整整数集合的内存空间大小uint32_t size = len*intrev32ifbe(is->encoding);is = zrealloc(is,sizeof(intset)+size);//sizeof(intset)是头需要存储的长度,size是数据的长度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. *///在集合is的底层数组中查找值value所在的索引;成功找到value时，函数返回1，并将*pos的值设为value所在的索引//当在数组中没找到 value 时，返回 0 。并将 *pos 的值设为 value 可以插入到数组中的位置。
static uint8_t intsetSearch(intset *is, int64_t value, uint32_t *pos) {//printf("---intsetSearch---%d,%d\n",value,*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) { //为空的情况if (pos) *pos = 0;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,max)) {  //和最后一个元素对比if (pos) *pos = intrev32ifbe(is->length);return 0;} else if (value < _intsetGet(is,0)) { //和第一个元素对比if (pos) *pos = 0;return 0;}}//二分查找while(max >= min) {mid = ((unsigned int)min + (unsigned int)max) >> 1;cur = _intsetGet(is,mid);  //获取值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;}
}/* Upgrades the intset to a larger encoding and inserts the given integer. */
//根据值 value 所使用的编码方式，对整数集合的编码进行升级，并将值 value 添加到升级后的整数集合中
static intset *intsetUpgradeAndAdd(intset *is, int64_t value) {uint8_t curenc = intrev32ifbe(is->encoding);//字节序转换uint8_t newenc = _intsetValueEncoding(value); //新value需要的编码int length = intrev32ifbe(is->length);int prepend = value < 0 ? 1 : 0;   //添加前端或末尾/* First set new encoding and resize */is->encoding = intrev32ifbe(newenc);  //改变编码方式is = intsetResize(is,intrev32ifbe(is->length)+1); //调整大小  /* 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));//复制旧值/* 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;
}static void intsetMoveTail(intset *is, uint32_t from, uint32_t to) {//向前或先后移动指定索引范围内的数组元素void *src, *dst;uint32_t bytes = intrev32ifbe(is->length)-from; //要移动元素的个数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);//memmove能够保证源串在被覆盖之前将重叠区域的字节拷贝到目标区域中
}/* Insert an integer in the intset */
intset *intsetAdd(intset *is, int64_t value, uint8_t *success) {//尝试将元素 value 添加到整数集合中uint8_t valenc = _intsetValueEncoding(value);uint32_t pos;if (success) *success = 1; //success指示添加是否成功/* 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. */printf("encoding =%d\n",intrev32ifbe(is->encoding)); if (valenc > intrev32ifbe(is->encoding)) {  //判断编码方式/* 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)) {  //成功找到value返回1，没找到返回0。并这只一个合适的pos值保证有序if (success) *success = 0;return is;}is = intsetResize(is,intrev32ifbe(is->length)+1);if (pos < intrev32ifbe(is->length)) intsetMoveTail(is,pos,pos+1);}_intsetSet(is,pos,value);is->length = intrev32ifbe(intrev32ifbe(is->length)+1);return is;
}/* Delete integer from intset */
intset *intsetRemove(intset *is, int64_t value, int *success) {//从整数集合中删除值valueuint8_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);is = intsetResize(is,len-1);is->length = intrev32ifbe(len-1);}return is;
}/* Determine whether a value belongs to this set */
uint8_t intsetFind(intset *is, int64_t value) {//检查给定值 value 是否集合中的元素uint8_t valenc = _intsetValueEncoding(value);return valenc <= intrev32ifbe(is->encoding) && intsetSearch(is,value,NULL);
}/* Return random member */
int64_t intsetRandom(intset *is) {//从整数集合中随机返回一个元素return _intsetGet(is,rand()%intrev32ifbe(is->length));
}/* Get the value at the given position. When this position is* out of range the function returns 0, when in range it returns 1. */
uint8_t intsetGet(intset *is, uint32_t pos, int64_t *value) {//取出集合底层数组指定位置中的值，并将它保存到value指针中if (pos < intrev32ifbe(is->length)) {*value = _intsetGet(is,pos);return 1;}return 0;
}/* Return intset length */
uint32_t intsetLen(const intset *is) {//返回整数集合现有的元素个数return intrev32ifbe(is->length);
}/* Return intset blob size in bytes. */
size_t intsetBlobLen(intset *is) {//返回整数集合现在占用的字节总数量return sizeof(intset)+intrev32ifbe(is->length)*intrev32ifbe(is->encoding);
}

整数集合会根据整数大小选择合适的编码方式，很节约内存。

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