archive/php-src
1
0
Fork 0
mirror of https://github.com/php/php-src.git synced 2025-08-18 15:08:55 +02:00
Code Issues Projects Releases Packages Wiki Activity Actions 1

Update bundled library to version 2.8.2.

Browse source 
Make OnUpdateInt compatible with ZE2.
Fix the makefile fragment for non-gnu makes
This commit is contained in:
Wez Furlong 2003-06-04 22:40:00 +00:00
parent 82a1818fde
commit 80e7f7001d
42 changed files with 11143 additions and 7558 deletions
Download patch file Download diff file Expand all files Collapse all files

80
ext/sqlite/libsqlite/src/encode.c
View file

@ -19,6 +19,86 @@
*/
#include <string.h>
/*
** How This Encoder Works
**
** The output is allowed to contain any character except 0x27 (') and
** 0x00. This is accomplished by using an escape character to encode
** 0x27 and 0x00 as a two-byte sequence. The escape character is always
** 0x01. An 0x00 is encoded as the two byte sequence 0x01 0x01. The
** 0x27 character is encoded as the two byte sequence 0x01 0x03. Finally,
** the escape character itself is encoded as the two-character sequence
** 0x01 0x02.
**
** To summarize, the encoder works by using an escape sequences as follows:
**
** 0x00 -> 0x01 0x01
** 0x01 -> 0x01 0x02
** 0x27 -> 0x01 0x03
**
** If that were all the encoder did, it would work, but in certain cases
** it could double the size of the encoded string. For example, to
** encode a string of 100 0x27 character would require 100 instances of
** the 0x01 0x03 escape sequence resulting in a 200-character output.
** We would prefer to keep the size of the encoded string smaller than
** this.
**
** To minimize the encoding size, we first add a fixed offset value to each
** byte in the sequence. The addition is module 256. (That is to say, if
** the sum of the original character value and the offset exceeds 256, then
** the higher order bits are truncated.) The offset is chosen to minimize
** the number of characters in the string that need to be escaped. For
** example, in the case above where the string was composed of 100 0x27
** characters, the offset might be 0x01. Each of the 0x27 characters would
** then be converted into an 0x28 character which would not need to be
** escaped at all and so the 100 character input string would be converted
** into just 100 characters of output. Actually 101 characters of output -
** we have to record the offset used as the first byte in the sequence so
** that the string can be decoded. Since the offset value is stored as
** part of the output string and the output string is not allowed to contain
** characters 0x00 or 0x27, the offset cannot be 0x00 or 0x27.
**
** Here, then, are the encoding steps:
**
** (1) Choose an offset value and make it the first character of
** output.
**
** (2) Copy each input character into the output buffer, one by
** one, adding the offset value as you copy.
**
** (3) If the value of an input character plus offset is 0x00, replace
** that one character by the two-character sequence 0x01 0x01.
** If the sum is 0x01, replace it with 0x01 0x02. If the sum
** is 0x27, replace it with 0x01 0x03.
**
** (4) Put a 0x00 terminator at the end of the output.
**
** Decoding is obvious:
**
** (5) Copy encoded characters except the first into the decode
** buffer. Set the first encoded character aside for use as
** the offset in step 7 below.
**
** (6) Convert each 0x01 0x01 sequence into a single character 0x00.
** Convert 0x01 0x02 into 0x01. Convert 0x01 0x03 into 0x27.
**
** (7) Subtract the offset value that was the first character of
** the encoded buffer from all characters in the output buffer.
**
** The only tricky part is step (1) - how to compute an offset value to
** minimize the size of the output buffer. This is accomplished to testing
** all offset values and picking the one that results in the fewest number
** of escapes. To do that, we first scan the entire input and count the
** number of occurances of each character value in the input. Suppose
** the number of 0x00 characters is N(0), the number of occurances of 0x01
** is N(1), and so forth up to the number of occurances of 0xff is N(256).
** An offset of 0 is not allowed so we don't have to test it. The number
** of escapes required for an offset of 1 is N(1)+N(2)+N(40). The number
** of escapes required for an offset of 2 is N(2)+N(3)+N(41). And so forth.
** In this way we find the offset that gives the minimum number of escapes,
** and thus minimizes the length of the output string.
*/
/*
** Encode a binary buffer "in" of size n bytes so that it contains
** no instances of characters '\'' or '\000'. The output is