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Fix <prevlen> related doc in ziplist.c 

According to the definition of ZIP_BIG_PREVLEN and other related code,
the guard of single byte <prevlen> should be 254 instead of 255.
This commit is contained in:
spacewander 2017-09-12 15:06:42 +08:00
parent 202c2ebec4
commit 63d361ff08
1 changed files with 10 additions and 10 deletions
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20
src/ziplist.c
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@ -53,20 +53,20 @@
* <prevlen> <encoding> * <prevlen> <encoding>
* *
* The length of the previous entry, <prevlen>, is encoded in the following way: * The length of the previous entry, <prevlen>, is encoded in the following way:
* If this length is smaller than 255 bytes, it will only consume a single * If this length is smaller than 254 bytes, it will only consume a single
* byte representing the length as an unsinged 8 bit integer. When the length * byte representing the length as an unsinged 8 bit integer. When the length
* is greater than or equal to 255, it will consume 5 bytes. The first byte is * is greater than or equal to 254, it will consume 5 bytes. The first byte is
* set to 255 (FF) to indicate a larger value is following. The remaining 4 * set to 254 (FE) to indicate a larger value is following. The remaining 4
* bytes take the length of the previous entry as value. * bytes take the length of the previous entry as value.
* *
* So practically an entry is encoded in the following way: * So practically an entry is encoded in the following way:
* *
* <prevlen from 0 to 254> <encoding> <entry> * <prevlen from 0 to 253> <encoding> <entry>
* *
* Or alternatively if the previous entry length is greater than 254 bytes * Or alternatively if the previous entry length is greater than 253 bytes
* the following encoding is used: * the following encoding is used:
* *
* 0xFF <4 bytes unsigned little endian prevlen> <encoding> <entry> * 0xFE <4 bytes unsigned little endian prevlen> <encoding> <entry>
* *
* The encoding field of the entry depends on the content of the * The encoding field of the entry depends on the content of the
* entry. When the entry is a string, the first 2 bits of the encoding first * entry. When the entry is a string, the first 2 bits of the encoding first
@ -191,10 +191,10 @@
#include "redisassert.h" #include "redisassert.h"
#define ZIP_END 255 /* Special "end of ziplist" entry. */ #define ZIP_END 255 /* Special "end of ziplist" entry. */
#define ZIP_BIG_PREVLEN 254 /* Max number of bytes of the previous entry, for #define ZIP_BIG_PREVLEN 254 /* ZIP_BIG_PREVLEN - 1 is the max number of bytes of
the "prevlen" field prefixing each entry, to be the previous entry, for the "prevlen" field prefixing
represented with just a single byte. Otherwise each entry, to be represented with just a single byte.
it is represented as FF AA BB CC DD, where Otherwise it is represented as FE AA BB CC DD, where
AA BB CC DD are a 4 bytes unsigned integer AA BB CC DD are a 4 bytes unsigned integer
representing the previous entry len. */ representing the previous entry len. */