85 lines
4.2 KiB
Plaintext
85 lines
4.2 KiB
Plaintext
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This is a nearly-public-domain reimplementation of the V8 regexp(3) package.
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It gives C programs the ability to use egrep-style regular expressions, and
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does it in a much cleaner fashion than the analogous routines in SysV.
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Copyright (c) 1986 by University of Toronto.
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Written by Henry Spencer. Not derived from licensed software.
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Permission is granted to anyone to use this software for any
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purpose on any computer system, and to redistribute it freely,
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subject to the following restrictions:
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1. The author is not responsible for the consequences of use of
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this software, no matter how awful, even if they arise
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from defects in it.
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2. The origin of this software must not be misrepresented, either
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by explicit claim or by omission.
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3. Altered versions must be plainly marked as such, and must not
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be misrepresented as being the original software.
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Barring a couple of small items in the BUGS list, this implementation is
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believed 100% compatible with V8. It should even be binary-compatible,
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sort of, since the only fields in a "struct regexp" that other people have
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any business touching are declared in exactly the same way at the same
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location in the struct (the beginning).
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This implementation is *NOT* AT&T/Bell code, and is not derived from licensed
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software. Even though U of T is a V8 licensee. This software is based on
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a V8 manual page sent to me by Dennis Ritchie (the manual page enclosed
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here is a complete rewrite and hence is not covered by AT&T copyright).
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The software was nearly complete at the time of arrival of our V8 tape.
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I haven't even looked at V8 yet, although a friend elsewhere at U of T has
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been kind enough to run a few test programs using the V8 regexp(3) to resolve
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a few fine points. I admit to some familiarity with regular-expression
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implementations of the past, but the only one that this code traces any
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ancestry to is the one published in Kernighan & Plauger (from which this
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one draws ideas but not code).
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Simplistically: put this stuff into a source directory, copy regexp.h into
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/usr/include, inspect Makefile for compilation options that need changing
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to suit your local environment, and then do "make r". This compiles the
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regexp(3) functions, compiles a test program, and runs a large set of
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regression tests. If there are no complaints, then put regexp.o, regsub.o,
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and regerror.o into your C library, and regexp.3 into your manual-pages
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directory.
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Note that if you don't put regexp.h into /usr/include *before* compiling,
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you'll have to add "-I." to CFLAGS before compiling.
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The files are:
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Makefile instructions to make everything
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regexp.3 manual page
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regexp.h header file, for /usr/include
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regexp.c source for regcomp() and regexec()
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regsub.c source for regsub()
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regerror.c source for default regerror()
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regmagic.h internal header file
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try.c source for test program
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timer.c source for timing program
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tests test list for try and timer
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This implementation uses nondeterministic automata rather than the
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deterministic ones found in some other implementations, which makes it
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simpler, smaller, and faster at compiling regular expressions, but slower
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at executing them. In theory, anyway. This implementation does employ
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some special-case optimizations to make the simpler cases (which do make
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up the bulk of regular expressions actually used) run quickly. In general,
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if you want blazing speed you're in the wrong place. Replacing the insides
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of egrep with this stuff is probably a mistake; if you want your own egrep
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you're going to have to do a lot more work. But if you want to use regular
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expressions a little bit in something else, you're in luck. Note that many
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existing text editors use nondeterministic regular-expression implementations,
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so you're in good company.
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This stuff should be pretty portable, given appropriate option settings.
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If your chars have less than 8 bits, you're going to have to change the
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internal representation of the automaton, although knowledge of the details
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of this is fairly localized. There are no "reserved" char values except for
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NUL, and no special significance is attached to the top bit of chars.
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The string(3) functions are used a fair bit, on the grounds that they are
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probably faster than coding the operations in line. Some attempts at code
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tuning have been made, but this is invariably a bit machine-specific.
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