X-Git-Url: https://fleuret.org/cgi-bin/gitweb/gitweb.cgi?p=finddup.git;a=blobdiff_plain;f=finddup.1;h=2da4ee3dc12e5b24d40182090bd9cfca0d4e2943;hp=46a4326fb9f2e1244aef1bfe9a93588f43505880;hb=8c988a4aca00501c9a9d53f4ff228dcb0bce0acb;hpb=e4133d06373b48e8509afd0811bb0a726d74f8a8

diff --git a/finddup.1 b/finddup.1
index 46a4326..2da4ee3 100644
--- a/finddup.1
+++ b/finddup.1
@@ -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
@@ -61,35 +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
 
 .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, hence it
-is off by default. 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.
+The current algorithm is dumb, as it does not use any hashing of the
+file content.
 
-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.
+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 never read entirely hence the md5s can not be properly computed,
+(2) computing XOR of the first 4, 16 and 256 bytes with rejection as
+soon as one does not match, (3) reading parts of the files of
+increasing sizes so that rejection could be done with a small fraction
+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"