[development][PCRE] old PCRE

介紹， man手冊 

txt版 http://www.pcre.org/original/pcre.txt

html版 http://www.pcre.org/original/doc/html/pcre.html

 

In addition to the Perl-compatible matching function, PCRE contains an alternative function that matches the same compiled patterns in a different way. 
In certain circumstances, the alternative function has some advantages. For a discussion of the two matching algorithms, see the pcrematching page.

pcrematching:

http://www.pcre.org/original/doc/html/pcrematching.html

摘要：

　　0.  是批量處理的意思？ 一個pattern處理多個subject麼？

The set of strings that are matched by a regular expression can be represented as a tree structure.

 

　　1.  Jeffrey Friedl's book "Mastering Regular Expressions"

　　中文版：精通正則表達式：https://book.douban.com/subject/2154713/

　　英文版PDF：https://doc.lagout.org/Others/O%27Reilly%20-%20Mastering%20Regular%20Expressions.pdf

　　2， PCRE匹配分標準接口(pcre_exec(), pcre16_exec() and pcre32_exec() functions. )和非標準接口( pcre_dfa_exec(), pcre16_dfa_exec() and pcre32_dfa_exec() functions )兩種。

　　　　前者在同一個串中只能返回一個匹配結果，或者能夠同時返回一個串中的多個匹配結果。

　　　　標準接口返回的結果有多是最長串，最短串或任意長度的串，這取決於貪婪與非貪婪的設置。

　　　　標準接口就是NFA algorithm是深度優先查找樹，同時能夠有貪婪（greedy）與非貪婪（ungreedy）兩種控制種類。

　　　　非標準接口爲廣度優先查找樹，爲DFA算法（ In Friedl's terminology, this is a kind of "DFA algorithm", though it is not implemented as a traditional finite state machine (it keeps multiple states active simultaneously).）subject串的掃描會一直進行到串的尾部或者沒有其餘須要遍歷的路徑。全部的已終結路徑即表明了所有的匹配結果，返回的結果按照字符串長度遞減。有一個開關設置第一個命中即返回，也就是最短命中串。

　　3.  非標準方法的優勢：

　　　　a， 匹配多個結果，尤爲是找到最長匹配。

　　　　b， 能夠對超長的subject數據進行屢次分批次的匹配。

　　　  非標準方法的缺點：

　　　　a， 比標準方法慢。

　　　　b， 不支持子串提取。

　　　　c， Although atomic groups are supported, their use does not provide the performance advantage that it does for the standard algorithm.

 

pcrejit:

http://www.pcre.org/original/doc/html/pcrejit.html

摘要：

　　JIT提供特別深度的優化. 犧牲額外的處理步驟，從而提升匹配性能。適合一次pattern編譯屢次match操做的應用場景。

　　1. 只支持標準PCRE接口，不支持DFA匹配模式。

　　2. PCRE默認不打開JIT，須要在編譯的時候增長--enable-jit選項。

　　3.  有硬件平臺限制

  ARM v5, v7, and Thumb2
  Intel x86 32-bit and 64-bit
  MIPS 32-bit
  Power PC 32-bit and 64-bit
  SPARC 32-bit (experimental)

　　4.  the pcre_jit_exec() function was not available at all before 8.32

　　5.  The JIT compiler generates different optimized code for each of the three modes (normal, soft partial, hard partial). When pcre_exec() is called, the appropriate code is run if it is available. Otherwise, the pattern is matched using interpretive code.

　　6.  There are some pcre_exec() options that are not supported for JIT execution. There are also some pattern items that JIT cannot handle. Details are given below. In both cases, execution automatically falls back to the interpretive code.

　　7.  Once a pattern has been studied, with or without JIT, it can be used as many times as you like for matching different subject strings.

　　8.   The code that is generated by the JIT compiler is architecture-specific, and is also position dependent. For those reasons it cannot be saved (in a file or database) and restored later like the bytecode and other data of a compiled pattern. 

　　more info: http://www.pcre.org/original/doc/html/pcreprecompile.html

　　9.  有時候JIT機器碼沒有成功編譯，可是pcre_exec()仍然正常運行，只不過fallback回了解釋碼。咱們在高性能場景下不但願使用解釋碼的時候，使用API pcre_jit_exec().

Because the API described above falls back to interpreted execution when JIT is not available, it is convenient for programs that are written 
for general use in many environments. However, calling JIT via pcre_exec() does have a performance impact. Programs that are written for use 
where JIT is known to be available, and which need the best possible performance, can instead use a "fast path" API to call JIT execution directly 
instead of calling pcre_exec() (obviously only for patterns that have been successfully studied by JIT).

 　　10.  pcre_exec()會作參數合法性的檢測。pcre_jit_exec()爲了提升性能，不作合法性檢測，若是參數不合法，結果沒法預期。

 

API: 

http://www.pcre.org/original/doc/html/pcreapi.html

摘要：

　　1，

The functions pcre_compile(), pcre_compile2(), pcre_study(), and pcre_exec() are used for compiling and matching regular expressions in a Perl-compatible manner.

　　2， compile a pattern

　　　　http://www.pcre.org/original/doc/html/pcreapi.html#SEC11

　　3,    studying a pattern

Studying a pattern does two things: first, a lower bound for the length of subject string that is needed to match the pattern is computed. This does not mean 
that there are any strings of that length that match, but it does guarantee that no shorter strings match. The value is used to avoid wasting time by trying 
to match strings that are shorter than the lower bound. 
Studying a pattern is also useful for non-anchored patterns that do not have a single fixed starting character. A bitmap of possible starting bytes is created. 
This speeds up finding a position in the subject at which to start matching.

　　4,   matching a pattern

However, it is possible to save compiled patterns and study data, and then use them later in different processes, possibly even on different hosts. 
For a discussion about this, see the pcreprecompile documentation.

 

對比一下PCRE2：

[development][PCRE] PCRE

 

 

trie:

https://zh.wikipedia.org/zh-hans/Trie

 

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黑哥的blog：http://www.cnblogs.com/zzqcn/p/3525636.html

這個講的很好，對比PCRE、PCRE-JIT，hyperscan：https://mp.weixin.qq.com/s?__biz=MzI3NDA4ODY4MA==&mid=2653334341&idx=1&sn=bf10ca6d8ca1452723b84a62f7fc436d&chksm=f0cb5cc2c7bcd5d4f423af8d78aeb58dd6d9494c1562b1e775579321df3b9f59a951656100d0&scene=21#wechat_redirect