/* ========================= HyperLogLog algorithm ========================= */
/* Our hash function is MurmurHash2, 64 bit version.
* It was modified for Redis in order to provide the same result in
* big and little endian archs (endian neutral). */
我们的hash函数用的是64位版本的MurmurHash2。
Redis使用时为了在大端和小端的结构中提供更好的结果修改了该算法
uint64_t MurmurHash64A (const void * key, int len, unsigned int seed) {
const uint64_t m = 0xc6a4a7935bd1e995; 初始化的值
const int r = 47; 常用轮数
uint64_t h = seed ^ (len * m); 种子 异或 ( 长度 乘以 初始化值 )
const uint8_t *data = (const uint8_t *)key; 获取数据初始位置
const uint8_t *end = data + (len-(len&7)); 获取模8结束位置
while(data != end) { 不到结尾
uint64_t k;
#if (BYTE_ORDER == LITTLE_ENDIAN) 小段情况
#ifdef USE_ALIGNED_ACCESS 字节对齐
memcpy(&k,data,sizeof(uint64_t));
#else
k = *((uint64_t*)data);
#endif
#else 大端情况
k = (uint64_t) data[0];
k |= (uint64_t) data[1] << 8;
k |= (uint64_t) data[2] << 16;
k |= (uint64_t) data[3] << 24;
k |= (uint64_t) data[4] << 32;
k |= (uint64_t) data[5] << 40;
k |= (uint64_t) data[6] << 48;
k |= (uint64_t) data[7] << 56;
#endif
k *= m; k 乘以 m
k ^= k >> r; k向右移动r位
k *= m; k 乘以 m
h ^= k; h 异或 k
h *= m; h 乘以 m
data += 8; 下一个8字节数据
}
switch(len & 7) { 剩下的不对齐8字节的数据处理
case 7: h ^= (uint64_t)data[6] << 48; /* fall-thru */
case 6: h ^= (uint64_t)data[5] << 40; /* fall-thru */
case 5: h ^= (uint64_t)data[4] << 32; /* fall-thru */
case 4: h ^= (uint64_t)data[3] << 24; /* fall-thru */
case 3: h ^= (uint64_t)data[2] << 16; /* fall-thru */
case 2: h ^= (uint64_t)data[1] << 8; /* fall-thru */
case 1: h ^= (uint64_t)data[0];
h *= m; /* fall-thru */
};
h ^= h >> r; h 异或 h向右移动r位
h *= m; h 乘以 m
h ^= h >> r; h 异或 h向右移动r位
return h; 返回最终h值
}
******************************************************************************************
/* Given a string element to add to the HyperLogLog, returns the length
* of the pattern 000..1 of the element hash. As a side effect 'regp' is
* set to the register index this element hashes to. */
给定一个字符串元素，添加到HyperLogLog，返回元素hash值的 按照模式000..1的长度。
作为一个副作用，变量regp被设置为这个元素所在寄存器的hash索引，即用regp标记寄存器
int hllPatLen(unsigned char *ele, size_t elesize, long *regp) {
uint64_t hash, bit, index;
int count;
/* Count the number of zeroes starting from bit HLL_REGISTERS
* (that is a power of two corresponding to the first bit we don't use
* as index). The max run can be 64-P+1 = Q+1 bits.
对HLL_REGISTERS的开始位置的0进行计数(这是一个2的指数，对应第一个我们不作为索引使用的比特位)
* Note that the final "1" ending the sequence of zeroes must be
* included in the count, so if we find "001" the count is 3, and
* the smallest count possible is no zeroes at all, just a 1 bit
* at the first position, that is a count of 1.
*注意到最后的1，结束序列0必须包含在计数中，所以我们找到001的计数是3，
最小的计数是可能一个前导零也没有，第一个比特位就是1，那么计数就是1
* This may sound like inefficient, but actually in the average case
* there are high probabilities to find a 1 after a few iterations. */
这个听起来不是那么有效，实际上在平均情况下，有很高的概率只需要少量迭代就可以发现一个为1的比特位
hash = MurmurHash64A(ele,elesize,0xadc83b19ULL);
index = hash & HLL_P_MASK; /* Register index. */ 寄存器的索引 HLL_P_MASK=2^14-1
hash >>= HLL_P; /* Remove bits used to address the register. */ 移出14个用于标记寄存器的比特位
hash |= ((uint64_t)1<<HLL_Q); /* Make sure the loop terminates and count will be <= Q+1. */
确保循环终止，并且计数小于等于Q+1
bit = 1;
count = 1; /* Initialized to 1 since we count the "00000...1" pattern. */ 初始化为1，因为我们计数为"00000...1"的模式
while((hash & bit) == 0) { 这里需要注意hash是小端表示，所以低地址放的是高位的数据，所以得到的模式是000...1的模式
count++;
bit <<= 1;
}
*regp = (int) index;
return count;
}
******************************************************************************************
/* ================== Dense representation implementation ================== */ 密集表示的实现
/* Low level function to set the dense HLL register at 'index' to the
* specified value if the current value is smaller than 'count'.
低层级的函数，如果当前值比计数值小的情况下，用来设置在索引位置的密集HLL寄存器为特定的值。
* 'registers' is expected to have room for HLL_REGISTERS plus an
* additional byte on the right. This requirement is met by sds strings
* automatically since they are implicitly null terminated.
寄存器期望在右边有一个字节的额外空间，这个需求sds字符串可以自动满足，因为隐式的含有一个null结尾字节
* The function always succeed, however if as a result of the operation
* the approximated cardinality changed, 1 is returned. Otherwise 0
* is returned. */
这个函数总是成功的，除了 操作导致基数值改变了就返回1，其它情况返回0
int hllDenseSet(uint8_t *registers, long index, uint8_t count) {
uint8_t oldcount;
HLL_DENSE_GET_REGISTER(oldcount,registers,index); 获取index所在寄存器的值
if (count > oldcount) {
HLL_DENSE_SET_REGISTER(registers,index,count); 设置index所在寄存器的值
return 1;
} else {
return 0;
}
}
******************************************************************************************
/* "Add" the element in the dense hyperloglog data structure.
* Actually nothing is added, but the max 0 pattern counter of the subset
* the element belongs to is incremented if needed.
在密集表示的HLL数据结构中添加元素。实际上没有添加任何内容，不过是最大的子集中模式0的基树可能增加
* This is just a wrapper to hllDenseSet(), performing the hashing of the
* element in order to retrieve the index and zero-run count. */
这个函数是函数hllDenseSet的封装，执行元素的hash为了获取索引和零行程的计数
int hllDenseAdd(uint8_t *registers, unsigned char *ele, size_t elesize) {
long index;
uint8_t count = hllPatLen(ele,elesize,&index);
/* Update the register if this element produced a longer run of zeroes. */ 更新寄存器 如果元素产生了一个更长的零行程
return hllDenseSet(registers,index,count);
}
******************************************************************************************
/* Compute the register histogram in the dense representation. */
计算密集表示中寄存器的直方图
void hllDenseRegHisto(uint8_t *registers, int* reghisto) {
int j;
/* Redis default is to use 16384 registers 6 bits each. The code works
* with other values by modifying the defines, but for our target value
* we take a faster path with unrolled loops. */
redis默认使用16384个6比特的寄存器。通过修改定义这个代码可以工作在其它的值下，
但是对我们目标值来说，采用了更快的展开循环的方式进行(获取更快的速度)
if (HLL_REGISTERS == 16384 && HLL_BITS == 6) {
uint8_t *r = registers;
unsigned long r0, r1, r2, r3, r4, r5, r6, r7, r8, r9,
r10, r11, r12, r13, r14, r15;
for (j = 0; j < 1024; j++) {
/* Handle 16 registers per iteration. */
r0 = r[0] & 63;
r1 = (r[0] >> 6 | r[1] << 2) & 63;
r2 = (r[1] >> 4 | r[2] << 4) & 63;
r3 = (r[2] >> 2) & 63;
r4 = r[3] & 63;
r5 = (r[3] >> 6 | r[4] << 2) & 63;
r6 = (r[4] >> 4 | r[5] << 4) & 63;
r7 = (r[5] >> 2) & 63;
r8 = r[6] & 63;
r9 = (r[6] >> 6 | r[7] << 2) & 63;
r10 = (r[7] >> 4 | r[8] << 4) & 63;
r11 = (r[8] >> 2) & 63;
r12 = r[9] & 63;
r13 = (r[9] >> 6 | r[10] << 2) & 63;
r14 = (r[10] >> 4 | r[11] << 4) & 63;
r15 = (r[11] >> 2) & 63;
reghisto[r0]++;
reghisto[r1]++;
reghisto[r2]++;
reghisto[r3]++;
reghisto[r4]++;
reghisto[r5]++;
reghisto[r6]++;
reghisto[r7]++;
reghisto[r8]++;
reghisto[r9]++;
reghisto[r10]++;
reghisto[r11]++;
reghisto[r12]++;
reghisto[r13]++;
reghisto[r14]++;
reghisto[r15]++;
r += 12; 12 * 8 = 16 * 6 一个字节是8比特，所以12个字节对应 16个6比特的寄存器
}
} else { //其它值的模式下，采用定义
for(j = 0; j < HLL_REGISTERS; j++) {
unsigned long reg;
HLL_DENSE_GET_REGISTER(reg,registers,j);
reghisto[reg]++;
}
}
}
******************************************************************************************
/* ================== Sparse representation implementation ================= */ 稀疏表示实现
/* Convert the HLL with sparse representation given as input in its dense
* representation. Both representations are represented by SDS strings, and
* the input representation is freed as a side effect.
对于输入为稀疏表示的HLL转化为密集表示。两种表示都使用SDS字符串，作为一种副作用，输入表示被释放(即函数调用之后，输入的表示不存了)
* The function returns C_OK if the sparse representation was valid,
* otherwise C_ERR is returned if the representation was corrupted. */
这个函数返回C_OK，如果稀疏表示是有效的，否则返回C_ERR，如果稀疏表示奔溃了
typedef struct redisObject {
unsigned type:4;
unsigned encoding:4;
unsigned lru:LRU_BITS; /* LRU time (relative to global lru_clock) or
* LFU data (least significant 8 bits frequency
* and most significant 16 bits access time). */
int refcount;
void *ptr;
} robj;
int hllSparseToDense(robj *o) {
sds sparse = o->ptr, dense;
struct hllhdr *hdr, *oldhdr = (struct hllhdr*)sparse; 旧HLL结构
int idx = 0, runlen, regval;
uint8_t *p = (uint8_t*)sparse, *end = p+sdslen(sparse); 获取结尾
/* If the representation is already the right one return ASAP. */
如果表示是我们需要的那个，立即返回
hdr = (struct hllhdr*) sparse;
if (hdr->encoding == HLL_DENSE) return C_OK;
/* Create a string of the right size filled with zero bytes.
* Note that the cached cardinality is set to 0 as a side effect
* that is exactly the cardinality of an empty HLL. */
创建一个用零填充的大小合适的字符串
注意这个缓存的基数被设置为0是一个副作用，正好是空HLL的基数
dense = sdsnewlen(NULL,HLL_DENSE_SIZE); 根据长度创建一个新字符串
hdr = (struct hllhdr*) dense;
*hdr = *oldhdr; /* This will copy the magic and cached cardinality. */ 将旧值赋值给新创建的字符串
hdr->encoding = HLL_DENSE; 编码类型设置为密集
/* Now read the sparse representation and set non-zero registers accordingly. */
现在读取稀疏表示并且设置对应非0寄存器
p += HLL_HDR_SIZE; 跳过结构体头部，指向数据部分
while(p < end) { 没有到结尾
if (HLL_SPARSE_IS_ZERO(p)) { 是零操作符
runlen = HLL_SPARSE_ZERO_LEN(p); 获取长度
idx += runlen;
p++;
} else if (HLL_SPARSE_IS_XZERO(p)) { X零操作符
runlen = HLL_SPARSE_XZERO_LEN(p);
idx += runlen;
p += 2;
} else {
runlen = HLL_SPARSE_VAL_LEN(p);
regval = HLL_SPARSE_VAL_VALUE(p);
if ((runlen + idx) > HLL_REGISTERS) break; /* Overflow. */
while(runlen--) {
HLL_DENSE_SET_REGISTER(hdr->registers,idx,regval);设置寄存器的值
idx++;
}
p++;
}
}
/* If the sparse representation was valid, we expect to find idx
* set to HLL_REGISTERS. */
如果稀疏表示是有效的，我们期望找到idx设置为HLL_REGISTERS
if (idx != HLL_REGISTERS) { 不是有效表示
sdsfree(dense);
return C_ERR;
}
/* Free the old representation and set the new one. */ 释放旧的表示 设置新值
sdsfree(o->ptr);
o->ptr = dense;
return C_OK;
}
******************************************************************************************
/* Low level function to set the sparse HLL register at 'index' to the
* specified value if the current value is smaller than 'count'.
底层的函数 用来设置索引位置的HLL稀疏寄存器的值，如果当前值小于计数值
* The object 'o' is the String object holding the HLL. The function requires
* a reference to the object in order to be able to enlarge the string if
* needed.
对象o是保存hll的字符串。这个函数需要一个对象的引用，为了能够在需要的时候扩大字符串
* On success, the function returns 1 if the cardinality changed, or 0
* if the register for this element was not updated.
* On error (if the representation is invalid) -1 is returned.
成功的情况下，如果基数改变了函数返回1，否则返回0如果这个元素的寄存器没有更新。
错误的情况下(如果这个表达式是无效的)，返回-1
* As a side effect the function may promote the HLL representation from
* sparse to dense: this happens when a register requires to be set to a value
* not representable with the sparse representation, or when the resulting
* size would be greater than server.hll_sparse_max_bytes. */
作为一个副作用，这个函数可能促进HLL的表示从稀疏转向密集：
这种情况发生在一个寄存器需要设置一个非稀疏表示的值，
或者这个结果的大小将大于定义的server.hll_sparse_max_bytes的值
int hllSparseSet(robj *o, long index, uint8_t count) {
struct hllhdr *hdr;
uint8_t oldcount, *sparse, *end, *p, *prev, *next;
long first, span;
long is_zero = 0, is_xzero = 0, is_val = 0, runlen = 0;
/* If the count is too big to be representable by the sparse representation
* switch to dense representation. */
如果计数太大了导致不能稀疏表示，转向密集表示
if (count > HLL_SPARSE_VAL_MAX_VALUE) goto promote;
如果超过了稀疏表示能表示的最大值，转向密集表示
/* When updating a sparse representation, sometimes we may need to
* enlarge the buffer for up to 3 bytes in the worst case (XZERO split
* into XZERO-VAL-XZERO). Make sure there is enough space right now
* so that the pointers we take during the execution of the function
* will be valid all the time. */
当更新稀疏表示时候，有时候在最差的情况下，我们需要扩大缓存增加3个字节(XZERO分裂为XZERO-VAL-XZERO).
请确保现在有足够的空间，以便我们在函数执行期间使用的指针始终有效。
o->ptr = sdsMakeRoomFor(o->ptr,3); 扩大了3个字节，确保指针有效
/* Step 1: we need to locate the opcode we need to modify to check
* if a value update is actually needed. */
步骤1，我们需要定位需要修改的操作符，检查是否需要更新值
sparse = p = ((uint8_t*)o->ptr) + HLL_HDR_SIZE; 开始位置
end = p + sdslen(o->ptr) - HLL_HDR_SIZE; 结束位置
first = 0;
prev = NULL; /* Points to previous opcode at the end of the loop. */ 在循环结束的时候，指向前一个操作码
next = NULL; /* Points to the next opcode at the end of the loop. */ 在循环结束的时候，指向下一个操作码
span = 0;
while(p < end) { 还没有结束
long oplen;
/* Set span to the number of registers covered by this opcode.
将span变量设置为这个操作码覆盖的寄存器
* This is the most performance critical loop of the sparse
* representation. Sorting the conditionals from the most to the
* least frequent opcode in many-bytes sparse HLLs is faster. */
这是稀疏表示中性能最关键的循环。将条件从多字节稀疏HLL中的最频繁操作码排序到最不频繁操作码达到最快的速度。
oplen = 1;
if (HLL_SPARSE_IS_ZERO(p)) { 短途的零操作最多
span = HLL_SPARSE_ZERO_LEN(p);
} else if (HLL_SPARSE_IS_VAL(p)) { 然后蚕食值操作
span = HLL_SPARSE_VAL_LEN(p);
} else { /* XZERO. */
span = HLL_SPARSE_XZERO_LEN(p); 最不频繁的就是长途的零
oplen = 2;
}
/* Break if this opcode covers the register as 'index'. */
如果当前操作码包含了寄存器index所在的位置,那么就不用往下找了
if (index <= first+span-1) break;
prev = p; 保存前一个操作码
p += oplen; 指向下一个操作码
first += span; 变更初始值
}
if (span == 0 || p >= end) return -1; /* Invalid format. */ 无效格式 跨度为0或者超过结尾，格式错误
next = HLL_SPARSE_IS_XZERO(p) ? p+2 : p+1; 指向下一个操作码
if (next >= end) next = NULL; 如果下一个操作码超过结尾，赋值为空
/* Cache current opcode type to avoid using the macro again and
* again for something that will not change.
* Also cache the run-length of the opcode. */
缓存当前操作码类型，以避免对不会更改的内容反复使用宏。同时缓存操作码的行程长度。
if (HLL_SPARSE_IS_ZERO(p)) {
is_zero = 1;
runlen = HLL_SPARSE_ZERO_LEN(p);
} else if (HLL_SPARSE_IS_XZERO(p)) {
is_xzero = 1;
runlen = HLL_SPARSE_XZERO_LEN(p);
} else {
is_val = 1;
runlen = HLL_SPARSE_VAL_LEN(p);
}
/* Step 2: After the loop:
*
* 'first' stores to the index of the first register covered
* by the current opcode, which is pointed by 'p'.
first保存p指向的 当前寄存器中保存的操作码
* 'next' ad 'prev' store respectively the next and previous opcode,
* or NULL if the opcode at 'p' is respectively the last or first.
*next和prev分辨保存下一个和前一个的操作码或者空，如果操作在p分别是最后一个或者第一个
* 'span' is set to the number of registers covered by the current
* opcode.
*span被设置为本当前操作码覆盖的寄存器数目(就是当前)
* There are different cases in order to update the data structure
* in place without generating it from scratch:
有多种不同的情况， 可以更新对应位置的数据结构而不用破坏原来的结构
* A) If it is a VAL opcode already set to a value >= our 'count'
* no update is needed, regardless of the VAL run-length field.
* In this case PFADD returns 0 since no changes are performed.
情况A,如果对应位置是一个值，并且大于我们需要更新的值count,不需要更新，
无论值的行程有多长。在这种情况下，PFADD返回0，因为没有任何更新需要执行
* B) If it is a VAL opcode with len = 1 (representing only our
* register) and the value is less than 'count', we just update it
* since this is a trivial case. */
情况B,如果恰好是一个值操作码，而且长度为1(只表示了我们当前所在的寄存器，就是p指向的寄存器)
并且值比我们的count小，我们只需要更新它即可，因为这也是一种平凡的情况，不需要改变原来的数据结构.
if (is_val) {
oldcount = HLL_SPARSE_VAL_VALUE(p);
/* Case A. */ 情况A,无需改变
if (oldcount >= count) return 0;
/* Case B. */ 情况B，值操作码长度为1，只需要更新值即可
if (runlen == 1) {
HLL_SPARSE_VAL_SET(p,count,1);
goto updated;
}
}
/* C) Another trivial to handle case is a ZERO opcode with a len of 1.
* We can just replace it with a VAL opcode with our value and len of 1. */
情况C，另外一个平凡的情况是 需要更新的值是一个长度为1的零操作码，我们只需要用长度为1的值操作码替代即可
if (is_zero && runlen == 1) { 需要更新的是长度为1的零操作码，直接用长度为1的值操作码更新即可
HLL_SPARSE_VAL_SET(p,count,1);
goto updated;
}
/* D) General case.
*一般情况,就是需要改变数据结构的情况
* The other cases are more complex: our register requires to be updated
* and is either currently represented by a VAL opcode with len > 1,
* by a ZERO opcode with len > 1, or by an XZERO opcode.
其它情况比较复杂：我们的寄存器需要更新，并且当前表达式是一个长度大于1的值操作码，
或者长度大于1的零操作码，或者XZERO操作码。
* In those cases the original opcode must be split into multiple
* opcodes. The worst case is an XZERO split in the middle resuling into
* XZERO - VAL - XZERO, so the resulting sequence max length is 5 bytes.
*在这些情况中，原始的操作码需要分裂成多个操作码。最坏的情况是一个XZERO在中间分裂成XZERO-VAL-XZERO，
这样导致序列最大长度为5个字节。
* We perform the split writing the new sequence into the 'new' buffer
* with 'newlen' as length. Later the new sequence is inserted in place
* of the old one, possibly moving what is on the right a few bytes
* if the new sequence is longer than the older one. */
我们执行分裂操作，将新序列写入到名为new实际长度为newlen的缓存.后续再将新序列插入到旧值原来的地方，
如果新值的长度超过旧值，那么可能需要向右移动几个字节。
uint8_t seq[5], *n = seq;
int last = first+span-1; /* Last register covered by the sequence. */ 最后一个被序列覆盖的寄存器
int len;
if (is_zero || is_xzero) { 原本是0序列， 短的零序列 和长的零序列
/* Handle splitting of ZERO / XZERO. */ 分裂 ZERO 或者 XZERO序列.
if (index != first) { 不是头部
len = index-first; 偏离头部长度
if (len > HLL_SPARSE_ZERO_MAX_LEN) { 超过了ZERO的最大长度，那么就是XZERO
HLL_SPARSE_XZERO_SET(n,len);
n += 2;
} else {
HLL_SPARSE_ZERO_SET(n,len);
n++;
}
}
HLL_SPARSE_VAL_SET(n,count,1);
n++;
if (index != last) { 如果不是尾部
len = last-index;偏离尾部的距离
if (len > HLL_SPARSE_ZERO_MAX_LEN) { 超过了ZERO的最大长度，那么就是XZERO
HLL_SPARSE_XZERO_SET(n,len);
n += 2;
} else {
HLL_SPARSE_ZERO_SET(n,len);
n++;
}
}
} else { 原本是个值
/* Handle splitting of VAL. */ 处理值的分裂情况，多个连续相同的原值
int curval = HLL_SPARSE_VAL_VALUE(p); 获取原值
if (index != first) { 不是头部
len = index-first;
HLL_SPARSE_VAL_SET(n,curval,len);
n++;
}
HLL_SPARSE_VAL_SET(n,count,1); 新值
n++;
if (index != last) {
len = last-index;
HLL_SPARSE_VAL_SET(n,curval,len);原值
n++;
}
}
/* Step 3: substitute the new sequence with the old one.
步骤3，用新的序列代替老的序列
* Note that we already allocated space on the sds string
* calling sdsMakeRoomFor(). */
注意到我们已经在sds字符串调用函数sdsMakeRoomFor()中分配空间
int seqlen = n-seq; 新值的长度
int oldlen = is_xzero ? 2 : 1; 旧值的长度
int deltalen = seqlen-oldlen; 两者差值
if (deltalen > 0 &&
sdslen(o->ptr)+deltalen > server.hll_sparse_max_bytes) goto promote; 如果超出了最大稀疏表示，就改用密集表示
if (deltalen && next) memmove(next+deltalen,next,end-next);
如果有新旧值长度有差值并且原值有后续操作码，那么向右移动后续的操作码，腾出新值所需的空间
sdsIncrLen(o->ptr,deltalen); 需改字符串的空间大小
memcpy(p,seq,seqlen); 将新值拷贝到上面腾出的空间中
end += deltalen; 尾部位置需要将新增加的空间计算上
updated:
/* Step 4: Merge adjacent values if possible.
*步骤4 如果可能就合并相邻的值
* The representation was updated, however the resulting representation
* may not be optimal: adjacent VAL opcodes can sometimes be merged into
* a single one. */
表达式被更新了，然而这个结果表达式可能不是最优的：相邻的值操作码能被合并到一个新的值操作码
p = prev ? prev : sparse; 指向前一个操作码，如果没有就从头开始
int scanlen = 5; /* Scan up to 5 upcodes starting from prev. */从前一个值开始扫描5个更新操作码字节，因为最长也就是5个
while (p < end && scanlen--) {
if (HLL_SPARSE_IS_XZERO(p)) {
p += 2;
continue;
} else if (HLL_SPARSE_IS_ZERO(p)) {
p++;
continue;
}
/* We need two adjacent VAL opcodes to try a merge, having
* the same value, and a len that fits the VAL opcode max len. */
我们需要合并相邻的值操作码，拥有相同的值，并且长度符合值操作码的最大长度
if (p+1 < end && HLL_SPARSE_IS_VAL(p+1)) {
int v1 = HLL_SPARSE_VAL_VALUE(p);
int v2 = HLL_SPARSE_VAL_VALUE(p+1);
if (v1 == v2) {
int len = HLL_SPARSE_VAL_LEN(p)+HLL_SPARSE_VAL_LEN(p+1); 将两个同样值的长度相加
if (len <= HLL_SPARSE_VAL_MAX_LEN) { 小于最大长度
HLL_SPARSE_VAL_SET(p+1,v1,len); 设置到p+1的位置
memmove(p,p+1,end-p); 向前移动一个位置
sdsIncrLen(o->ptr,-1); 字符串长度减去一个位置
end--;
/* After a merge we reiterate without incrementing 'p'
* in order to try to merge the just merged value with
* a value on its right. */
经过合并，我们在不增加p的情况下，重复尝试合并刚合并的值和它右边的值
continue;
}
}
}
p++; 前后两个都是值，不用合并的情况下，向后移动一位，继续尝试合并
}
/* Invalidate the cached cardinality. */ 使得存储的基数无效
hdr = o->ptr;
HLL_INVALIDATE_CACHE(hdr);
return 1;
promote: /* Promote to dense representation. */ 变化为密集表示
if (hllSparseToDense(o) == C_ERR) return -1; /* Corrupted HLL. */ 变成密集表示失败
hdr = o->ptr;
/* We need to call hllDenseAdd() to perform the operation after the
* conversion. However the result must be 1, since if we need to
* convert from sparse to dense a register requires to be updated.
*在转化为密集表示后，我们需要调用hllDenseAdd去执行操作修改旧值，
这个结果必须为1，因为我们从稀疏转向密集，必定有寄存器需要修改，否则不需要转密集
* Note that this in turn means that PFADD will make sure the command
* is propagated to slaves / AOF, so if there is a sparse -> dense
* conversion, it will be performed in all the slaves as well. */
注意，这反过来意味着PFADD将确保命令被传播到slaves/AOF，
因此如果存在稀疏->密集转换，它也将在所有slave中执行
int dense_retval = hllDenseSet(hdr->registers,index,count);
serverAssert(dense_retval == 1); 确保为1
return dense_retval;
}
******************************************************************************************
/* "Add" the element in the sparse hyperloglog data structure.
* Actually nothing is added, but the max 0 pattern counter of the subset
* the element belongs to is incremented if needed.
在稀疏表示的HLL数据结构中添加元素。实际上什么也没有添加。但是如果所属子集的最大0模式的计数增加，将会做出变动。
* This function is actually a wrapper for hllSparseSet(), it only performs
* the hashshing of the elmenet to obtain the index and zeros run length. */
这个函数实际上是对hllSparseSet的封装。它只是执行元素hash函数来获取位置和零行程的长度
int hllSparseAdd(robj *o, unsigned char *ele, size_t elesize) {
long index;
uint8_t count = hllPatLen(ele,elesize,&index); 获取统计的零行程长度
/* Update the register if this element produced a longer run of zeroes. */ 更新寄存器如果元素馋了一个更长的零行程
return hllSparseSet(o,index,count);
}
******************************************************************************************
/* Compute the register histogram in the sparse representation. */
计算稀疏表示中寄存器的直方图
void hllSparseRegHisto(uint8_t *sparse, int sparselen, int *invalid, int* reghisto) {
int idx = 0, runlen, regval;
uint8_t *end = sparse+sparselen, *p = sparse;
while(p < end) { 序列没有结束
if (HLL_SPARSE_IS_ZERO(p)) { 是0行程
runlen = HLL_SPARSE_ZERO_LEN(p);
idx += runlen;
reghisto[0] += runlen; 零个数的统计
p++;
} else if (HLL_SPARSE_IS_XZERO(p)) {
runlen = HLL_SPARSE_XZERO_LEN(p);
idx += runlen;
reghisto[0] += runlen; 零个数的统计
p += 2;
} else {
runlen = HLL_SPARSE_VAL_LEN(p);
regval = HLL_SPARSE_VAL_VALUE(p);
idx += runlen;
reghisto[regval] += runlen; 值个数的统计
p++;
}
}
if (idx != HLL_REGISTERS && invalid) *invalid = 1; 寄存器个数正确并且传入的invalid非空，赋值invalid为1
}
******************************************************************************************
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