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ziplist.c explanation of format improved a bit.

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antirez 2016-12-16 09:04:57 +01:00
parent ac61f90625
commit d634c36253
1 changed files with 19 additions and 12 deletions
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31
src/ziplist.c
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@ -8,24 +8,31 @@
* *
* ---------------------------------------------------------------------------- * ----------------------------------------------------------------------------
* *
* ZIPLIST OVERALL LAYOUT: * ZIPLIST OVERALL LAYOUT
* The general layout of the ziplist is as follows:
* <zlbytes><zltail><zllen><entry><entry><zlend>
* *
* <zlbytes> is an unsigned integer to hold the number of bytes that the * The general layout of the ziplist is as follows:
* ziplist occupies. This value needs to be stored to be able to resize the *
* <zlbytes> <zltail> <zllen> <entry> <entry> ... <entry> <zlend>
*
* All fields are stored in little endian.
*
* <uint32_t zlbytes> is an unsigned integer to hold the number of bytes that
* the ziplist occupies. This value needs to be stored to be able to resize the
* entire structure without the need to traverse it first. * entire structure without the need to traverse it first.
* *
* <zltail> is the offset to the last entry in the list. This allows a pop * <uint32_t zltail> is the offset to the last entry in the list. This allows
* operation on the far side of the list without the need for full traversal. * a pop operation on the far side of the list without the need for full
* traversal.
* *
* <zllen> is the number of entries.When this value is larger than 2**16-2, * <uint16_t zllen> is the number of entries. When this value is larger
* we need to traverse the entire list to know how many items it holds. * than 2^16-2, we need to traverse the entire list to know how many items it
* holds.
* *
* <zlend> is a single byte special value, equal to 255, which indicates the * <uint8_t zlend> is a single byte special value, equal to 255, which
* end of the list. * indicates the end of the list.
*
* ZIPLIST ENTRIES
* *
* ZIPLIST ENTRIES:
* Every entry in the ziplist is prefixed by a header that contains two pieces * Every entry in the ziplist is prefixed by a header that contains two pieces
* of information. First, the length of the previous entry is stored to be * of information. First, the length of the previous entry is stored to be
* able to traverse the list from back to front. Second, the encoding with an * able to traverse the list from back to front. Second, the encoding with an