1. compression problem...
i'm developing a new compression algorithm designed for plain text
documents(no ASCII values above 7 bits, or ASCII 127). here's how it
works: my program takes all the bits of every byte, replaces the last
bit with the first bit of the next byte. then that first bit of the next
byte is removed and a 0 inserted at the end. this process is repeated
until the last byte - 1. this should leave some ASCII 0 bytes after a
while, right? well for some odd reason, it doesn't...i dunno, maybe i'm
having an off day and made a mistake in my code. in either case, here it
is:
[comp1.ex]
include file.e
include get.e
include machine.e
function lof(integer fn)
integer pos,eof
pos=where(fn)
if seek(fn,-1) then end if
eof=where(fn)
if seek(fn,pos) then end if
return eof
end function
with trace
sequence stuff,cmd,inf,outf,stuff2,tmp,tmp2
integer fn,decompress
decompress=0
cmd=command_line()
if length(cmd) < 4 then
puts(1,"Experimental Plain Text Compression\n")
puts(1,"usage: ex eptc [-d] infile outfile\n")
puts(1,"\nDefault behavior is compression. -d causes it to
decompress\n")
abort(0)
end if
if equal(cmd[3],"-d") then
decompress=1
cmd=cmd[1..2]&cmd[4..length(cmd)]
end if
inf=cmd[3] outf=cmd[4]
if not decompress then
puts(1,"Compressing...\n")
fn=open(inf,"rb")
if fn=-1 then
printf(1,"Unable to open `%s'\n",inf)
abort(1)
end if
stuff=get_bytes(fn,lof(fn))
close(fn)
stuff2=""
for i = 1 to length(stuff)-1 do
tmp=int_to_bits(stuff[i],8)
if tmp[8] != 0 then
puts(1,"Error: this file is not all plain text. Convert it to plain
text(if it's a Word document or something) and remove all graphics
characters, then try again\n")
abort(3)
end if
tmp2=int_to_bits(stuff[i+1],7)
tmp=tmp[1..7]&tmp2[1]
stuff[i+1]=bits_to_int(tmp2[2..length(tmp2)]&0)
stuff2 &= bits_to_int(tmp)
end for
stuff2 &= stuff[length(stuff)]
stuff={}
for i = 1 to length(stuff2) do
stuff2[i]=int_to_bits(stuff2[i],8)
? stuff2[i]
if not equal(stuff2[i],repeat(0,8)) then
stuff &= bits_to_int(stuff2[i])
end if
end for
fn=open(outf,"wb")
if fn=-1 then
printf(1,"Unable to open `%s' for writing\n",outf)
abort(2)
end if
puts(fn,stuff)
close(fn)
else
puts(1,"Decompressing...")
fn=open(inf,"rb")
if fn=-1 then
printf(1,"Unable to open `%s'\n",inf)
abort(1)
end if
stuff=get_bytes(fn,lof(fn))
close(fn)
for i = 1 to length(stuff) do
stuff[i]=int_to_bits(stuff[i],8)
end for
for i = 1 to length(stuff)-1 do
stuff[i+1]=stuff[i][8]&stuff[i+1]
stuff[i]=stuff[i][1..length(stuff[i])-1]&0
end for
for i = 1 to length(stuff) do
stuff[i]=bits_to_int(stuff[i])
end for
fn=open(outf,"wb")
puts(fn,stuff)
close(fn)
end if
3. Re: compression problem...
On 25 Sep 2001, at 15:04, Sabal.Mike at notations.com wrote:
>
> Maybe I'm missing something here, but it looks like all you're trying to do is
> left-shift every word. I don't see where the compression would come in that.
> Also, if you're trying to bit-shift yourself into a number of null-bytes, this
> method would only work on byte=#80.
Ditto.
> It seems what you'd rather do for this simple algorithm is compress 8-bit
> bytes
> into 7-bit bytes by bit-shifting across the entire file, not just a single
> word.
> It would guarantee you a minimum 12.5% compression, and leave a greater
> chance
> of null or further compressable bytes. It might look something like this:
This would be useful only on those languages that use only the lower 7 bits,
too, how many languages would this leave out?
Kat
