Package: num-utils
Version: 0.5-3
Severity: wishlist
File: /usr/bin/numgrep
For example, this is pretty slow, it takes a few minutes
on my 800mhz PIII:
% seq 1 1000001 | numgrep /f777777/
I notice it still checks even after the top factor is reached:
# ts: timestamp standard input (from 'moreutils' package)
% { seq 1 100000 | numgrep /f7/ ; echo end ; } | ts
14:43:41 1
14:43:41 7
14:43:56 end
...in a way, that's 15 seconds wasted.
Possible speedups...
Let 'F' = the factor. Sort a copy of list, and use in a dimensional array,
e.g.:
% echo "3
5
1
"
...our linked list array would look like:
N list(N) sort(N) flag(N)
1 3 1 true
2 5 3 true
3 1 5 true
...then set the flag, linked to both 'sort(N)' and 'list(N)' according
to various tests. Apologies for not describing more completely how the
linked list should work. This is only a sketch.
Get prime factors using 'factor F' (in 'coreutils) and use those to
reduce the set. Don't search for numbers higher than 'F'. Stuff like
that.
PS: 'numgrep' is a handy utility!
-- System Information:
Debian Release: testing/unstable
APT prefers unstable
APT policy: (500, 'unstable'), (1, 'experimental')
Architecture: i386 (i686)
Shell: /bin/sh linked to /bin/dash
Kernel: Linux 2.6.16-2-686
Locale: LANG=C, LC_CTYPE=C (charmap=ANSI_X3.4-1968) (ignored: LC_ALL set to C)
Versions of packages num-utils depends on:
ii perl 5.8.8-6 Larry Wall's Practical Extraction
num-utils recommends no packages.
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