Function pfmergeCommand

app/redis-6.2.6/src/hyperloglog.c:1310–1381

PFMERGE dest src1 src2 src3 ... srcN => OK */

/* PFMERGE dest src1 src2 src3 ... srcN => OK */
void pfmergeCommand(client *c) {
    uint8_t max[HLL_REGISTERS];
    struct hllhdr *hdr;
    int j;
    int use_dense = 0; /* Use dense representation as target? */

    /* Compute an HLL with M[i] = MAX(M[i]_j).
     * We store the maximum into the max array of registers. We'll write
     * it to the target variable later. */
    memset(max,0,sizeof(max));
    for (j = 1; j < c->argc; j++) {
        /* Check type and size. */
        robj *o = lookupKeyRead(c->db,c->argv[j]);
        if (o == NULL) continue; /* Assume empty HLL for non existing var. */
        if (isHLLObjectOrReply(c,o) != C_OK) return;

        /* If at least one involved HLL is dense, use the dense representation
         * as target ASAP to save time and avoid the conversion step. */
        hdr = o->ptr;
        if (hdr->encoding == HLL_DENSE) use_dense = 1;

        /* Merge with this HLL with our 'max' HLL by setting max[i]
         * to MAX(max[i],hll[i]). */
        if (hllMerge(max,o) == C_ERR) {
            addReplyError(c,invalid_hll_err);
            return;
        }
    }

    /* Create / unshare the destination key's value if needed. */
    robj *o = lookupKeyWrite(c->db,c->argv[1]);
    if (o == NULL) {
        /* Create the key with a string value of the exact length to
         * hold our HLL data structure. sdsnewlen() when NULL is passed
         * is guaranteed to return bytes initialized to zero. */
        o = createHLLObject();
        dbAdd(c->db,c->argv[1],o);
    } else {
        /* If key exists we are sure it's of the right type/size
         * since we checked when merging the different HLLs, so we
         * don't check again. */
        o = dbUnshareStringValue(c->db,c->argv[1],o);
    }

    /* Convert the destination object to dense representation if at least
     * one of the inputs was dense. */
    if (use_dense && hllSparseToDense(o) == C_ERR) {
        addReplyError(c,invalid_hll_err);
        return;
    }

    /* Write the resulting HLL to the destination HLL registers and
     * invalidate the cached value. */
    for (j = 0; j < HLL_REGISTERS; j++) {
        if (max[j] == 0) continue;
        hdr = o->ptr;
        switch(hdr->encoding) {
        case HLL_DENSE: hllDenseSet(hdr->registers,j,max[j]); break;