This formula barely compresses , like .9% to 2% after 40 loops.
It gives you a little insight ... the "1100" combination , hardly ever happens, in real data..
How would you write an analyzer function , to see which combinations of bits are the mostly likely to occur???
given:
00
01
10
11
What combinations occur most and which ones the least??
Code: Select all
Declare Function compress_loop( chrs as string ) as string
Declare Function decompress_loop( chrs as string ) as string
'=============================================================================
'coderjeff's code.
'======================================================================================
const MAX_WORDS = 4
dim shared words( 0 to MAX_WORDS-1 ) as string
sub init_words()
words(0) = "00"
words(1) = "11"
words(2) = "0001"
words(3) = "1100"
end sub
function string_to_bits( byref s as const string ) as string
dim ret as string = ""
for i as integer = 0 to len(s)-1
ret &= bin( s[i], 8 )
next
function = ret
end function
function bits_to_string( byref s as const string ) as string
dim ret as string = ""
'' assume input length is multiple of 8
assert( (len(s) mod 8) = 0 )
for i as integer = 1 to len(s) step 8
ret &= chr( cubyte( "&b" & mid( s, i, 8 ) ) )
next
function = ret
end function
function encode( byref s as const string ) as string
dim bits as string = ""
'' loop through every byte in 's'
for i as ulongint = 0 to len(s) - 1
dim b as ubyte = s[i]
'' look at each pair of bits, most significant to least significant
for j as integer = 0 to 7 step 2
'' look up word from the dictionary
bits &= words( cint( "&b" & mid( bin( b, 8 ), j+1, 2 ) ) )
next
next
'' pad bits to multiple of 8
bits &= string( (8 - (len(bits) mod 8) mod 8), "0" )
function = bits_to_string( bits )
end function
function decode( byref s as const string, byval n as integer ) as string
dim bits as string = string_to_bits( s )
dim i as integer = 1, count as integer = 0
dim ret as string = ""
'' loop through entire bit string
while i <= len(bits) and (count < n*8 )
'' check for words
for j as integer = 0 to MAX_WORDS-1
if( mid( bits, i, len(words(j)) ) = words(j) ) then
ret &= bin( j, 2 )
i += len(words(j))
count += 2
continue while
end if
next
print "bad input for decode"
exit while
wend
function = bits_to_string( ret )
end function
init_words()
'=============================================================================
'=============================================================================
Namespace Zlibrary
#inclib "zlib"
Extern "C"
Declare Function compressBound(Byval sourceLen As Ulong) As Ulong
Declare Function uncompress(Byval dest As Ubyte Ptr, Byval destLen As Uinteger Ptr, Byval source As Ubyte Ptr, Byval sourceLen As Ulong) As Long
Declare Function compress(Byval dest As Ubyte Ptr, Byval destLen As Uinteger Ptr, Byval source As Ubyte Ptr, Byval sourceLen As Ulong) As Long
End Extern
Function getpassedinfo(text As String,Byref passed_length As Integer) As String
Dim As String var1,var2
Dim As Integer pst
#macro splice(stri,char,var1,var2)
pst=Instr(stri,char)
var1="":var2=""
If pst<>0 Then
var1=Mid(stri,1,pst-1)
var2=Mid(stri,pst+1)
Else
var1=stri
End If
#endmacro
splice(text,"|",var1,var2)
text=var2
passed_length=Valint(var1)
Return text
End Function
'================= UNPACK ===============
Function unpack(file As String) As String
Dim As Integer passed_length
Dim As String text=getpassedinfo(file,passed_length)
Dim As Integer stringlength,destinationlength
stringlength=Len(text)
destinationlength =passed_length
Dim As Ubyte Ptr source
Dim As Ubyte Ptr destination =Callocate(destinationlength,1)
source=@text[0]
Var mistake=uncompress(destination,@destinationlength, source, stringlength)
If mistake<>0 Then Print "There was an error":Sleep:End
Dim As String uncompressed
uncompressed=String(destinationlength,0)
For i As Integer = 0 To destinationlength- 1
uncompressed[i]=(destination[i])
Next
Deallocate destination
Return uncompressed
End Function
'=================== PACK ============
Function pack(file As String) As String
Dim As String text=file
Dim As Integer stringlength,destinationlength
stringlength=Len(text)
destinationlength = compressBound(stringlength)
Dim As Ubyte Ptr source
Dim As Ubyte Ptr destination =Callocate(destinationlength,1)
source=@text[0]
Var mistake=compress(destination, @destinationlength, source, stringlength)
If mistake <>0 Then Print "There was an error"
Dim As String compressed
compressed=String(destinationlength,0)
For n As Integer=0 To destinationlength-1
compressed[n]=destination[n]
Next n
compressed=stringlength &"|"+compressed
Deallocate destination
Return compressed
End Function
End Namespace
'==================================================================
'==================================================================
'test zipper
'==================================================================
'==================================================================
screen 19
Dim Shared As String s
Randomize
s=""
dim as string check=""
dim as string compare=""
dim as longint length = 0
dim as double compression = 0
dim as longint loops = 0
do
loops+=1
'one time run , create initial string
if loops = 1 then
For n As Long = 1 To 8000
s+=chr(Int(Rnd*256))'+48)
Next
compare = s
length = len(s)
else
'modify compression to make further compression possible
s = compress_loop(s)
end if
check = s
compression = (100 - ( 100 / ( length / len(check) ) ))
Print "original string"
Print Len(s)
Print
Dim As String compressed=Zlibrary.pack(s)
s = compressed
Print "packed string "
Print Len(compressed)
Print
Dim As String uncompressed=Zlibrary.unpack(compressed)
Print "Retrieve"
Print Len(uncompressed)
Print
'Print "compression ratio "; 100 - ( 100 / ( Len(s) / len(compressed) ) ) ; "%"
Print "compression ratio "; 100 - ( 100 / ( length / len(s) ) ) ; "%"
Print Iif(uncompressed=check,"OK","ERROR")
Print "-------------------------------"
'sleep 1000
'if loops > 2 and (100 - ( 100 / ( length / len(s) ) )) < compression then exit do
print "press a key for next compression."
print
print "press esc to exit."
sleep
if inkey = chr(27) then exit do
loop until loops = 40
print "Press a key to decompress."
sleep
s = str(loops) + "_" + s ' save as an output file...
'==================================================================
'decompress
'==================================================================
dim as longint dec = instr(1,s,"_")
dim as longint count = val(left(s,dec-1))
dim as string comp = mid(s,dec+1)
dim as string val1
dim as string outs
for a as longint = count to 2 step -1
s = Zlibrary.unpack(comp)
outs = decompress_loop(s)
comp = outs
next
comp = Zlibrary.unpack(comp)
print
print "input = "; length , "output = " ; len(comp) , "compression ratio "; 100 - ( 100 / ( length / len(s) ) ) ; "%"
print
if comp = compare then print "Decompression successful." else print "ERROR"
print
Print "!!~~Done~~!!"
Sleep
end
'===============================================================================
'===============================================================================
'begin functions
'===============================================================================
'===============================================================================
Function compress_loop( chrs as string ) as string
dim as string final_out = encode( chrs )
return final_out
end function
'===============================================================================
'============================================================================
Function decompress_loop( chrs as string ) as string
dim as string final_out = decode( chrs , len(chrs) )
return final_out
end function