Fixed the version number.

[finddup.git] / finddup.1

diff --git a/finddup.1 b/finddup.1
index faaef4d..62ab0b8 100644 (file)
--- a/finddup.1
+++ b/finddup.1
@@ -1,4 +1,4 @@
-.TH "FINDDUP" 1 "Mar 2010" "Francois Fleuret" "User Commands"
+.TH "FINDDUP" "1.0" "Mar 2010" "Francois Fleuret" "User Commands"
 
 \" This man page was written by Francois Fleuret <francois@fleuret.org>
 \" and is distributed under a Creative Commons Attribution-Share Alike
@@ -10,12 +10,13 @@ finddup \- Find files common to two directories (or not)
 
 .SH "SYNOPSIS"
 
-\fBfinddup\fP [OPTION]... DIR1 [[and:|not:]DIR2]
+\fBfinddup\fP [OPTION]... [DIR1 [[and:|not:]DIR2]]
 
 .SH "DESCRIPTION"
 
-With a single directory argument, \fBfinddup\fP prints the duplicated
-files found in it.
+With one directory as argument, \fBfinddup\fP prints the duplicated
+files found in it. If no directory is provided, it uses the current
+one as default.
 
 With two directories, it prints either the files common to both DIR1
 and DIR2 or, with the `not:' prefix, the ones present in DIR1 and not
@@ -61,38 +62,29 @@ show the real path of the files
 .TP
 \fB-i\fR, \fB--same-inodes-are-different\fR
 files with same inode are considered as different
-.TP
-\fB-m\fR, \fB--md5\fR
-use MD5 hashing (if compiled with the option)
 
 .SH "BUGS"
 
 None known, probably many. Valgrind does not complain though.
 
-The MD5 hashing is not satisfactory. It is computed for a file only if
-the said file has to be read fully for a comparison (i.e. two files
-match and we have to read them completely).
-
-Hence, in practice lot of partial MD5s are computed, which costs a lot
-of cpu and is useless. This often hurts more than it helps. The only
-case when it should really be useful is when you have plenty of
-different files of same size, and lot of similar ones, which does not
-happen often.
-
-Forcing the files to be read fully so that the MD5s are properly
-computed is not okay neither, since it would fully read certain files,
-even if we will never need their MD5s.
+The current algorithm is dumb, as it does not use any hashing of the
+file content.
 
-Anyway, it has to be compiled in with 'make WITH_MD5=yes', and even in
-that case it will be off by default
+Here are the things I tried, which did not help at all: (1) Computing
+md5s on the whole files, which is not satisfactory because files are
+often not read entirely, hence the md5s can not be properly computed,
+(2) computing XORs of the first 4, 16 and 256 bytes with rejection as
+soon as one does not match, (3) reading files in parts of increasing
+sizes so that rejection could be done with only a small fraction read
+when possible, (4) using mmap instead of open/read.
 
 .SH "WISH LIST"
 
 The format of the output should definitely be improved. Not clear how.
 
 Their could be some fancy option to link two instances of the command
-running on different machines to reduce network disk accesses. Again,
-this may not help much, for the reason given above.
+running on different machines to reduce network disk accesses. This
+may not help much though.
 
 .SH "EXAMPLES"