CSE320/hw2/doc/par.doc

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*********************
* par.doc *
* for Par 3.20 *
* Copyright 1993 by *
* Adam M. Costello *
*********************
Par 3.20 is a package containing:
+ This doc file.
+ A man page based on this doc file.
+ The ANSI C source for the filter "par".
Contents
Contents
File List
Rights and Responsibilities
Release Notes
Compilation
Synopsis
Description
Options
Environment
Details
Diagnostics
Examples
Limitations
Bugs
File List
The Par 3.20 package is always distributed with at least the following
files:
buffer.h
buffer.c
failf.h
failf.c
par.1
par.c
par.doc
protoMakefile
reformat.h
reformat.c
Each file is a text file which identifies itself on the second line, and
identifies the version of Par to which it belongs on the third line,
so you can always tell which file is which even if the files have been
renamed.
The file "par.1" is a man page for the filter par (not to be confused
with the package Par, which contains the source code for par). "par.1"
is based on this doc file, and conveys much (not all) of the same
information, but "par.doc" is the definitive documentation for both par
and Par.
Rights and Responsibilities
The files listed in the Files List section above are each Copyright 1993
by Adam M. Costello (henceforth "I").
I grant everyone permission to use these files in any way, subject to
the following two restrictions:
1) No one may distribute modifications of any of the files unless I am
the one who modified them.
2) No one may distribute any one of the files unless it is accompanied
by all of the other files.
I cannot disallow the distribution of patches, but I would prefer that
users send me suggestions for changes so that I can incorporate them
into future versions of Par. See the Bugs section for my addresses.
Though I have tried to make sure that Par is free of bugs, I make no
guarantees about its soundness. Therefore, I am not responsible for any
damage resulting from the use of these files.
Compilation
To compile par, you need an ANSI C compiler. Copy protoMakefile to
Makefile and edit it, following the instructions in the comments. Then
use make (or the equivalent on your system) to compile par.
If you have no make, compile each .c file into an object file and link
all the object files together by whatever method works on your system.
Then go look for a version of make that works on your system, since it
will come in handy in the future.
If your compiler warns you about a pointer to a constant being converted
to a pointer to a non-constant in line 289 of reformat.c, ignore it.
Your compiler (like mine) is in error. What it thinks is a pointer to
a constant is actually a pointer to a pointer to a constant, which is
something quite different. The conversion is legal, and a true ANSI C
compiler wouldn't complain.
If your compiler generates any other warnings that you think are
legitimate, please tell me about them (see the Bugs section).
Synopsis
par [w<width>] [p<prefix>] [s<suffix>] [h[<hang>]] [l[<last>]]
[m[<min>]] [version]
Things enclosed in [square brackets] are optional. Things enclosed in
<angle brackets> are variables.
Any option may be immediately preceeded by a minus sign (-).
Description
par is a filter which copies its input to its output, reformatting each
paragraph. Paragraphs are delimited by blank lines.
Each output paragraph is generated from the corresponding input lines as
follows:
1. An optional prefix and/or suffix is removed from each input line.
2. The remainder is divided into words (delimited by white space).
3. The words are joined into lines to make an eye-pleasing paragraph.
4. The prefixes and suffixes are reattached.
Options
All options except version are used to set values of variables. Values
set by command line options hold for all paragraphs in the input. Unset
variables are given default values which are recomputed separately for
each paragraph.
The approximate role of each variable is described here. See the
Details section for a much more complete and precise description.
w<width> Sets the value of <width>, the maximum width of the output
paragraph, in characters, not including the trailing newline
characters. Must be an unsigned decimal integer greater than
<prefix> (see below). Defaults to 72. If <width> is 9 or
more, the w is not needed.
p<prefix> Sets the value of <prefix>, the length of the prefix, in
characters. Must be an unsigned decimal integer. Defaults to
0 if there are no more than <hang> + 1 lines in the input
paragraph (see the h option). Otherwise defaults to the
length of the longest common prefix of all lines in the
input paragraph except the first <hang> of them. The first
<prefix> characters of each output line are copied from the
first <prefix> characters of the corresponding input line. If
<prefix> is 8 or less, the p is not needed.
s<suffix> Sets the value of <suffix>, the length of the suffix, in
characters. Must be an unsigned decimal integer. Defaults to
0 if there is no more than 1 line in the input paragraph.
Otherwise defaults to the length of the longest common suffix
of all lines in the input paragraph, after this common suffix
has been stripped of all initial white characters save the
last. The last <suffix> characters of each output line are
copied from the last <suffix> characters of the corresponding
input line.
h[<hang>] Sets the value of <hang>. Must be an unsigned decimal
integer. Defaults to 0. Mainly affects the default value of
<prefix> (see the p option). If the h option is given without
a number, the value 1 is assumed.
l[<last>] Sets the value of <last>. Must be 0 or 1. Defaults to 0. If
<last> is 1, par tries to make the last line of the output
paragraph about the same length as the others. If the l
option is given without a number, the value 1 is assumed.
m[<min>] Sets the value of <min>. Must be 0 or 1. Defaults to <last>.
If <min> is 1, par will try to make the paragraph narrower
without shortening the shortest line. If the m option is
given without a number, the value 1 is assumed.
version Causes all other options to be ignored. No input is read.
"par 3.20" is printed on the output. Of course, this will
change in future releases of Par.
If the value of any variable is set more than once, the last value is
used. For each paragraph, default values for any variables not set by
command line options are computed in the following order:
<width> <hang> <last> <min> <prefix> <suffix>
No integer appearing in an option may exceed 9999.
It is an error if <width> <= <prefix> + <suffix>.
Environment
If the environment variable PARINIT is set, par will read command line
options from it before it reads them from the command line.
Details
The white characters are the space, formfeed, newline, carriage return,
tab, and vertical tab.
Lines are terminated by newline characters, but the newlines are not
considered to be included in the lines. If the last character of the
input is a non-newline, then a newline will be inferred immediately
after it (but if the input is empty, no newline will be inferred; the
number of input lines will be 0). Thus, the input can always be viewed
as a sequence of lines.
A line is called blank if and only if it contains no non-white
characters. A subsequence of non-blank lines is called maximal if and
only if there is no non-blank line immediately before or after it.
The process described in the remainder of this section is applied
independently to each maximal subsequence of non-blank input lines.
(Each blank line of the input is transformed into an empty line on the
output).
After the values of the variables are determined (see the Options
section), the first <prefix> characters and the last <suffix> characters
of each input line are removed and remembered. It is an error for any
line to contain fewer than <prefix> + <suffix> characters.
The remaining text is treated as a sequence of characters, not lines.
The text is broken into words, which are delimited by white characters.
That is, a word is a maximal sub-sequence of non-white characters. If
there is at least one word, and the first word is preceeded only by
spaces (strictly spaces, not other white characters), then the first
word is expanded to include those spaces.
Let <L> = <width> - <prefix> - <suffix>.
Every word which contains more than <L> characters is broken, after each
<L>th character, into multiple words.
These words are reassembled, preserving their order, into lines.
Adjacent words within a line are separated by a single space.
If all the words fit on a single line of no more than <L> characters,
then no line breaks are inserted. Otherwise, line breaks are placed in
such a way that the resulting paragraph satisfies certain properties. If
<min> is 1, those properties are:
1. No line contains more than <L> characters.
2. The shortest line is as long as possible, subject to 1.
3. The longest line is as short as possible, subject to properties 1
and 2. Call its length <newL>.
4. The sum of the squares of the differences between <newL> and the
lengths of the lines is as small as possible, subject to properties
1, 2, and 3.
If <last> is 0, then the last line does not count as a line for the
purposes of properties 2 and 4 above.
If <min> is 0, then property 3 is disregarded, and <newL> is set equal
to <L>.
If the number of lines in the resultant paragraph is less than <hang>,
then empty lines are added at the end to bring the number of lines up to
<hang>.
If <suffix> is not 0, then each line is padded at the end with spaces to
bring its length up to <newL>.
To each line is prepended <prefix> characters. Let <n> be the number of
input lines. The characters which are prepended to the <i>th line are
chosen as follows:
1. If <i> <= <n>, then the characters are copied from the ones that
were removed from the beginning of the <n>th input line.
2. If <i> > <n> > <hang>, then the characters are copied from the ones
that were removed from the beginning of the last input line.
3. If <i> > <n> and <n> <= <hang>, then the characters are all spaces.
Then to each line is appended <suffix> characters. The characters which
are appended to the <i>th line are chosen as follows:
1. If <i> <= <n>, then the characters are copied from the ones that
were removed from the end of the nth input line.
2. If <i> > <n> > 0, then the characters are copied from the ones that
were removed from the end of the last input line.
3. If <n> = 0, then the characters are all spaces.
Finally, the lines are printed to the output.
Diagnostics
If there are no errors, par returns EXIT_SUCCESS (see <stdlib.h>).
If there is an error, then an error message will be printed to the
output, and par will return EXIT_FAILURE. If the error is local to a
single paragraph, then the preceeding paragraphs will have been output
before the error was detected. Line numbers in error messages are local
to the input paragraph in which the error occurred.
Of course, trying to print an error message would be futile if an error
resulted from an output function, so par doesn't bother doing any error
checking on output functions.
Examples
The superiority of par's dynamic programming algorithm over a greedy
algorithm (such as the one used by fmt) can be seen in the following
example:
Original paragraph:
We hold these truths to be self evident,
that all men are created equal,
that they are endowed by their creator
with certain unalienable rights,
that among these are
life, liberty, and the
pursuit of happiness.
After a greedy algorithm with width = 61:
We hold these truths to be self evident, that all men
are created equal, that they are endowed by their
creator with certain unalienable rights, that among
these are life, liberty, and the pursuit of
happiness.
After "par 61":
We hold these truths to be self evident, that all
men are created equal, that they are endowed by
their creator with certain unalienable rights, that
among these are life, liberty, and the pursuit of
happiness.
The line breaks chosen by par are clearly more pleasing.
I use par in conjunction with the !} command of the vi editor. Other
editors probably provide a similar feature for filtering text.
The rest of this section is a series of before-and-after pictures
showing some typical uses of par.
Before:
Four score and seven years ago, our fathers brought
forth on this continent
a new nation.
After "par 42":
Four score and seven years ago,
our fathers brought forth on this
continent a new nation.
Before:
/* Four score and seven years */
/* ago, our */
/* fathers brought forth on this continent */
/* a new nation. */
After "par 42":
/* Four score and seven years */
/* ago, our fathers brought */
/* forth on this continent a */
/* new nation. */
Or after "par l 42":
/* Four score and seven */
/* years ago, our fathers */
/* brought forth on this */
/* continent a new nation. */
Or after "par l 42 m0":
/* Four score and seven */
/* years ago, our fathers */
/* brought forth on this */
/* continent a new nation. */
Before:
Gettysburg Address: Four score
and seven years ago,
our fathers brought forth on
this continent
a new nation.
After "par h 56":
Gettysburg Address: Four score and seven years
ago, our fathers brought
forth on this continent a
new nation.
Before:
1 Four score and
2 seven years ago,
3 our fathers brought
4 forth on this continent
5 a new nation.
After "par p11 44":
1 Four score and seven years ago,
2 our fathers brought forth on this
3 continent a new nation.
Limitations
If you like two spaces between sentences, too bad. Differentiating
between periods that end sentences and periods used in abbreviations is
a complex problem beyond the scope of this simple filter. Consider the
following tough case:
I calc'd the approx.
Fermi level to 3 sig. digits.
Suppose that that should be reformatted to:
I calc'd the approx. Fermi
level to three sig. digits.
The program has to decide whether to put 1 or 2 spaces between "approx."
and "Fermi". There is no obvious hint from the original paragraph
because there was a line break between them, and "Fermi" begins with a
capital letter. The program would apparently have to understand English
grammar to determine that the sentence does not end there (and then it
would only work for English text).
If you use tabs, you probably won't like the way par handles (or doesn't
handle) them. It treats them just like spaces. I didn't bother trying
to make sense of tabs because they don't make sense to begin with. Not
everyone's terminal has the same tab settings, so text files containing
tabs are sometimes mangled. In fact, almost every text file containing
tabs gets mangled when something is inserted at the beginning of each
line (when quoting e-mail or commenting out a section of a shell script,
for example), making them a pain to edit. In my opinion, the world would
be a nicer place if everyone stopped using tabs (so I'm doing my part by
not supporting them in par.)
There is currently no way for the length of the output prefix to differ
from the length of the input prefix. Ditto for the suffix. I may
consider adding this capability in a future release, but right now I'm
not sure how I'd want it to work.
Bugs
If I knew of any bugs, I wouldn't have released the package. Of course,
there may be bugs that I haven't yet discovered.
If you find any bugs, or if you have any suggestions, please send e-mail
to:
amc@wuecl.wustl.edu
or send paper mail to:
Adam M. Costello
Campus Box 1045
Washington University
One Brookings Dr.
St. Louis, MO 63130
USA
Note that both addresses could change anytime after June 1994.
When reporting a bug, please include the exact input and command line
options used, and the version number of par, so that I can reproduce it.