对intset的更新和扩容，不是关键核心的代码：

/* 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;
}

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);
}

/* Insert an integer in the intset */
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. */
        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;
        }

        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) {
    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);
        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) {
    uint8_t valenc = _intsetValueEncoding(value);
    return valenc <= intrev32ifbe(is->encoding) && intsetSearch(is,value,NULL);
}

/* Return random member */
int64_t intsetRandom(intset *is) {
    uint32_t len = intrev32ifbe(is->length);
    assert(len); /* avoid division by zero on corrupt intset payload. */
    return _intsetGet(is,rand()%len);
}

/* 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;
}

/* Return intset length */
uint32_t intsetLen(const intset *is) {
    return intrev32ifbe(is->length);
}

/* Return intset blob size in bytes. */
size_t intsetBlobLen(intset *is) {
    return sizeof(intset)+(size_t)intrev32ifbe(is->length)*intrev32ifbe(is->encoding);
}

/* Validate the integrity of the data structure.
 * when `deep` is 0, only the integrity of the header is validated.
 * when `deep` is 1, we make sure there are no duplicate or out of order records. */
int intsetValidateIntegrity(const unsigned char *p, size_t size, int deep) {
    intset *is = (intset *)p;
    /* check that we can actually read the header. */
    if (size < sizeof(*is))
        return 0;

    uint32_t encoding = intrev32ifbe(is->encoding);

    size_t record_size;
    if (encoding == INTSET_ENC_INT64) {
        record_size = INTSET_ENC_INT64;
    } else if (encoding == INTSET_ENC_INT32) {
        record_size = INTSET_ENC_INT32;
    } else if (encoding == INTSET_ENC_INT16){
        record_size = INTSET_ENC_INT16;
    } else {
        return 0;
    }

    /* check that the size matchies (all records are inside the buffer). */
    uint32_t count = intrev32ifbe(is->length);
    if (sizeof(*is) + count*record_size != size)
        return 0;

    /* check that the set is not empty. */
    if (count==0)
        return 0;

    if (!deep)
        return 1;

    /* check that there are no dup or out of order records. */
    int64_t prev = _intsetGet(is,0);
    for (uint32_t i=1; i<count; i++) {
        int64_t cur = _intsetGet(is,i);
        if (cur <= prev)
            return 0;
        prev = cur;
    }

    return 1;
}

#ifdef REDIS_TEST
#include <sys/time.h>
#include <time.h>

#if 0
static void intsetRepr(intset *is) {
    for (uint32_t i = 0; i < intrev32ifbe(is->length); i++) {
        printf("%lld\n", (uint64_t)_intsetGet(is,i));
    }
    printf("\n");
}

static void error(char *err) {
    printf("%s\n", err);
    exit(1);
}
#endif

static void ok(void) {
    printf("OK\n");
}

static long long usec(void) {
    struct timeval tv;
    gettimeofday(&tv,NULL);
    return (((long long)tv.tv_sec)*1000000)+tv.tv_usec;
}

static intset *createSet(int bits, int size) {
    uint64_t mask = (1<<bits)-1;
    uint64_t value;
    intset *is = intsetNew();

    for (int i = 0; i < size; i++) {
        if (bits > 32) {
            value = (rand()*rand()) & mask;
        } else {
            value = rand() & mask;
        }
        is = intsetAdd(is,value,NULL);
    }
    return is;
}

static void checkConsistency(intset *is) {
    for (uint32_t i = 0; i < (intrev32ifbe(is->length)-1); i++) {
        uint32_t encoding = intrev32ifbe(is->encoding);

        if (encoding == INTSET_ENC_INT16) {
            int16_t *i16 = (int16_t*)is->contents;
            assert(i16[i] < i16[i+1]);
        } else if (encoding == INTSET_ENC_INT32) {
            int32_t *i32 = (int32_t*)is->contents;
            assert(i32[i] < i32[i+1]);
        } else {
            int64_t *i64 = (int64_t*)is->contents;
            assert(i64[i] < i64[i+1]);
        }
    }
}

#define UNUSED(x) (void)(x)
int intsetTest(int argc, char **argv, int accurate) {
    uint8_t success;
    int i;
    intset *is;
    srand(time(NULL));

    UNUSED(argc);
    UNUSED(argv);
    UNUSED(accurate);

    printf("Value encodings: "); {
        assert(_intsetValueEncoding(-32768) == INTSET_ENC_INT16);
        assert(_intsetValueEncoding(+32767) == INTSET_ENC_INT16);
        assert(_intsetValueEncoding(-32769) == INTSET_ENC_INT32);
        assert(_intsetValueEncoding(+32768) == INTSET_ENC_INT32);
        assert(_intsetValueEncoding(-2147483648) == INTSET_ENC_INT32);
        assert(_intsetValueEncoding(+2147483647) == INTSET_ENC_INT32);
        assert(_intsetValueEncoding(-2147483649) == INTSET_ENC_INT64);
        assert(_intsetValueEncoding(+2147483648) == INTSET_ENC_INT64);
        assert(_intsetValueEncoding(-9223372036854775808ull) ==
                    INTSET_ENC_INT64);
        assert(_intsetValueEncoding(+9223372036854775807ull) ==
                    INTSET_ENC_INT64);
        ok();
    }

    printf("Basic adding: "); {
        is = intsetNew();
        is = intsetAdd(is,5,&success); assert(success);
        is = intsetAdd(is,6,&success); assert(success);
        is = intsetAdd(is,4,&success); assert(success);
        is = intsetAdd(is,4,&success); assert(!success);
        ok();
        zfree(is);
    }

    printf("Large number of random adds: "); {
        uint32_t inserts = 0;
        is = intsetNew();
        for (i = 0; i < 1024; i++) {
            is = intsetAdd(is,rand()%0x800,&success);
            if (success) inserts++;
        }
        assert(intrev32ifbe(is->length) == inserts);
        checkConsistency(is);
        ok();
        zfree(is);
    }

    printf("Upgrade from int16 to int32: "); {
        is = intsetNew();
        is = intsetAdd(is,32,NULL);
        assert(intrev32ifbe(is->encoding) == INTSET_ENC_INT16);
        is = intsetAdd(is,65535,NULL);
        assert(intrev32ifbe(is->encoding) == INTSET_ENC_INT32);
        assert(intsetFind(is,32));
        assert(intsetFind(is,65535));
        checkConsistency(is);
        zfree(is);

        is = intsetNew();
        is = intsetAdd(is,32,NULL);
        assert(intrev32ifbe(is->encoding) == INTSET_ENC_INT16);
        is = intsetAdd(is,-65535,NULL);
        assert(intrev32ifbe(is->encoding) == INTSET_ENC_INT32);
        assert(intsetFind(is,32));
        assert(intsetFind(is,-65535));
        checkConsistency(is);
        ok();
        zfree(is);
    }

    printf("Upgrade from int16 to int64: "); {
        is = intsetNew();
        is = intsetAdd(is,32,NULL);
        assert(intrev32ifbe(is->encoding) == INTSET_ENC_INT16);
        is = intsetAdd(is,4294967295,NULL);
        assert(intrev32ifbe(is->encoding) == INTSET_ENC_INT64);
        assert(intsetFind(is,32));
        assert(intsetFind(is,4294967295));
        checkConsistency(is);
        zfree(is);

        is = intsetNew();
        is = intsetAdd(is,32,NULL);
        assert(intrev32ifbe(is->encoding) == INTSET_ENC_INT16);
        is = intsetAdd(is,-4294967295,NULL);
        assert(intrev32ifbe(is->encoding) == INTSET_ENC_INT64);
        assert(intsetFind(is,32));
        assert(intsetFind(is,-4294967295));
        checkConsistency(is);
        ok();
        zfree(is);
    }

    printf("Upgrade from int32 to int64: "); {
        is = intsetNew();
        is = intsetAdd(is,65535,NULL);
        assert(intrev32ifbe(is->encoding) == INTSET_ENC_INT32);
        is = intsetAdd(is,4294967295,NULL);
        assert(intrev32ifbe(is->encoding) == INTSET_ENC_INT64);
        assert(intsetFind(is,65535));
        assert(intsetFind(is,4294967295));
        checkConsistency(is);
        zfree(is);

        is = intsetNew();
        is = intsetAdd(is,65535,NULL);
        assert(intrev32ifbe(is->encoding) == INTSET_ENC_INT32);
        is = intsetAdd(is,-4294967295,NULL);
        assert(intrev32ifbe(is->encoding) == INTSET_ENC_INT64);
        assert(intsetFind(is,65535));
        assert(intsetFind(is,-4294967295));
        checkConsistency(is);
        ok();
        zfree(is);
    }

    printf("Stress lookups: "); {
        long num = 100000, size = 10000;
        int i, bits = 20;
        long long start;
        is = createSet(bits,size);
        checkConsistency(is);

        start = usec();
        for (i = 0; i < num; i++) intsetSearch(is,rand() % ((1<<bits)-1),NULL);
        printf("%ld lookups, %ld element set, %lldusec\n",
               num,size,usec()-start);
        zfree(is);
    }

    printf("Stress add+delete: "); {
        int i, v1, v2;
        is = intsetNew();
        for (i = 0; i < 0xffff; i++) {
            v1 = rand() % 0xfff;
            is = intsetAdd(is,v1,NULL);
            assert(intsetFind(is,v1));

            v2 = rand() % 0xfff;
            is = intsetRemove(is,v2,NULL);
            assert(!intsetFind(is,v2));
        }
        checkConsistency(is);
        ok();
        zfree(is);
    }

    return 0;
}
#endif