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Redis源码-整数集合intset

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源码位置：intset.c/intset.h

intset用来实现redis的set对象的数据结构之一（当元素较少且为数字类型时）。
为了节省内存的使用，创建intset的时候，使用最小的int类型（int16_t），当插入的整数大于int16_t时，将会进行对应的字节提升（int32_t或者int64_t），这种提升是不可逆的。

特点：

  1. 元素类型只有数字。
  2. 元素有三种类型，int16_t, int32_t, int64_t
  3. 元素有序且不可重复
  4. 内存连续，类似数组。

结构体与宏定义

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typedef struct intset {
    uint32_t encoding; // 编码类型 int16_t、int32_t、int64_t
    uint32_t length; // 长度 最大长度:2^32
    int8_t contents[]; // 柔性数组
} intset;

/* Note that these encodings are ordered, so:
 * 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))

函数功能总览

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intset *intsetNew(void); // 创建空的整数集合
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(const intset *is);
size_t intsetBlobLen(intset *is);

主要函数实现

私有函数：

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// 判断数值类型
/* 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;
}

// 获取intset指定位置的值
/* Return the value at pos, given an encoding. */
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) {
    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) {
    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);
    }
}

创建：

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/* Create an empty intset. */
intset *intsetNew(void) {
    intset *is = zmalloc(sizeof(intset)); // 分配空间
    is->encoding = intrev32ifbe(INTSET_ENC_INT16); // 默认元素大小为2字节 intrev32ifbe:如果cpu是大端模式，则转为小端模式
    is->length = 0;
    return is;
}
// 内存重新分配(删除、新增时)
/* Resize the intset */
static intset *intsetResize(intset *is, uint32_t len) {
    uint32_t size = len*intrev32ifbe(is->encoding);
    is = zrealloc(is,sizeof(intset)+size);
    return is;
}

增加：

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/* Insert an integer in the intset */
intset *intsetAdd(intset *is, int64_t value, uint8_t *success) {
    // 根据value的长度获取其编码
    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. */
    // 如果value的编码大于目前的encoding，需要整体提高encoding的大小
    if (valenc > intrev32ifbe(is->encoding)) {
        /* This always succeeds, so we don't need to curry *success. */
        // 执行扩大已经插入操作
        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. */
        // 查找元素的位置，如果该元素存在，则插入失败
        if (intsetSearch(is,value,&pos)) {
            if (success) *success = 0;
            return is;
        }
        // 如果元素不存在，则给intset扩容一个元素大小的空间
        is = intsetResize(is,intrev32ifbe(is->length)+1);
        if (pos < intrev32ifbe(is->length)) intsetMoveTail(is,pos,pos+1);
    }
    //插入元素到intset中
    _intsetSet(is,pos,value);
    // 更新intset的length
    is->length = intrev32ifbe(intrev32ifbe(is->length)+1);
    return is;
}
// 提高intset的encoding大小，并插入元素
/* 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); // 当前的编码
    uint8_t newenc = _intsetValueEncoding(value); // 新的编码
    int length = intrev32ifbe(is->length);
    // prepend用来确定新value的插入位置：第一个还是最后一个，因为它的encoding比is->encoding要大，所以它要么比目前所有元素都大，要么比所有元素都小，即插入位置要么第一个，要么最后一个。
    int prepend = value < 0 ? 1 : 0;

    /* First set new encoding and resize */
    is->encoding = intrev32ifbe(newenc);
    is = intsetResize(is,intrev32ifbe(is->length)+1); // 扩充一个元素大小的空间

    /* 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. */
    // 整体提高encoding大小
    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;
}
// 在指定位置插入value
/* Set the value at pos, using the configured encoding. */
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);
    }
}

// 当插入，或者删除时，需要进行元素挪动，比如，在pos位置插入一个元素时，pos后的所有元素都需要往后移（整体移动）
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);
}

查找：

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// 根据位置查找元素
/* 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) {
    if (pos < intrev32ifbe(is->length)) {
        *value = _intsetGet(is,pos);
        return 1;
    }
    return 0;
}

// 判断intset中是否有此元素
/* Determine whether a value belongs to this set */
uint8_t intsetFind(intset *is, int64_t value) {
    uint8_t valenc = _intsetValueEncoding(value);
    return valenc <= intrev32ifbe(is->encoding) && intsetSearch(is,value,NULL);
}

/* 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. */
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 */
    // 如果intset为空，未查找到value，则pos=0
    if (intrev32ifbe(is->length) == 0) {
        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. */
        // 如果intset末尾的元素小于value，则pos=length，如果value小于intset首位的元素，则pos=0
        if (value > _intsetGet(is,max)) {
            if (pos) *pos = intrev32ifbe(is->length);
            return 0;
        } else if (value < _intsetGet(is,0)) {
            if (pos) *pos = 0;
            return 0;
        }
    }
    // 二分法查找元素
    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;
        }
    }
    // 如果查找到，返回元素的位置，没找到，就返回具体位置
    if (value == cur) {
        if (pos) *pos = mid;
        return 1;
    } else {
        if (pos) *pos = min;
        return 0;
    }
}

删除：

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/* Delete integer from intset */
intset *intsetRemove(intset *is, int64_t value, int *success) {
    uint8_t valenc = _intsetValueEncoding(value);
    uint32_t pos;
    if (success) *success = 0;
    // 查找到元素的位置pos
    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 */
        // 查到元素后，删除该元素，并将pos后的所有元素向前移动
        if (pos < (len-1)) intsetMoveTail(is,pos+1,pos);
        is = intsetResize(is,len-1); // 重新分配intset内存
        is->length = intrev32ifbe(len-1);
    }
    return is;
}