漫话Redis源码之三

看了一下宏的实现，这是zle结构的高效的原因之一：

} zlentry;

#define ZIPLIST_ENTRY_ZERO(zle) { \
    (zle)->prevrawlensize = (zle)->prevrawlen = 0; \
    (zle)->lensize = (zle)->len = (zle)->headersize = 0; \
    (zle)->encoding = 0; \
    (zle)->p = NULL; \
}

/* Extract the encoding from the byte pointed by 'ptr' and set it into
 * 'encoding' field of the zlentry structure. */
#define ZIP_ENTRY_ENCODING(ptr, encoding) do {  \
    (encoding) = ((ptr)[0]); \
    if ((encoding) < ZIP_STR_MASK) (encoding) &= ZIP_STR_MASK; \
} while(0)

#define ZIP_ENCODING_SIZE_INVALID 0xff
/* Return the number of bytes required to encode the entry type + length.
 * On error, return ZIP_ENCODING_SIZE_INVALID */
static inline unsigned int zipEncodingLenSize(unsigned char encoding) {
    if (encoding == ZIP_INT_16B || encoding == ZIP_INT_32B ||
        encoding == ZIP_INT_24B || encoding == ZIP_INT_64B ||
        encoding == ZIP_INT_8B)
        return 1;
    if (encoding >= ZIP_INT_IMM_MIN && encoding <= ZIP_INT_IMM_MAX)
        return 1;
    if (encoding == ZIP_STR_06B)
        return 1;
    if (encoding == ZIP_STR_14B)
        return 2;
    if (encoding == ZIP_STR_32B)
        return 5;
    return ZIP_ENCODING_SIZE_INVALID;
}

#define ZIP_ASSERT_ENCODING(encoding) do {                                     \
    assert(zipEncodingLenSize(encoding) != ZIP_ENCODING_SIZE_INVALID);         \
} while (0)

/* Return bytes needed to store integer encoded by 'encoding' */
static inline unsigned int zipIntSize(unsigned char encoding) {
    switch(encoding) {
    case ZIP_INT_8B:  return 1;
    case ZIP_INT_16B: return 2;
    case ZIP_INT_24B: return 3;
    case ZIP_INT_32B: return 4;
    case ZIP_INT_64B: return 8;
    }
    if (encoding >= ZIP_INT_IMM_MIN && encoding <= ZIP_INT_IMM_MAX)
        return 0; /* 4 bit immediate */
    /* bad encoding, covered by a previous call to ZIP_ASSERT_ENCODING */
    redis_unreachable();
    return 0;
}