Michael Cotherman wrote:
>>....... is the decoding code, it does what you
>>describe below. It is adding the zeros back in, that
>>is the dst.append('\0')
>>
>>Kent
>
> Really??? I am a noob, but it looks like it only puts
> a \0 at the end if code (the length) is less than 255,
> as the if statement is out of the for loop? this would
> be part of the coding algorithm, no?
It puts 0 at the end of each segment if the length of the segment is less than
FF. In the original C code, the for loop is copying the data of a segment. The
while loop in both codes is looping over segments.
Here is my understanding of the algorithm (with maybe a few fine details left
out):
To encode:
- look for the first 0 byte in the data
- if it is more than FE bytes from the start, write out and FF and the first FE
bytes. This is a segment that *doesn't* end with a 0.
- otherwise write out (1+the number of bytes before the 0), then all the bytes
before the zero. Skip the input pointer to the byte after the 0.
- repeat until no more data
To decode:
- get the next byte from the data. This is the count
- get the next (count-1) bytes from the data and append to the output
- if count < FF then this segment ends with a 0, so append a 0 to the output.
- repeat until no more data
Oh, I see you already wrote the same thing in your previous email!
Kent
>
> In that theme of writing, here is what I would do to
> make it decode:
>
>
> def UnStuffData(src,dst,len):
> if code == 0xFF:
> pass
> else:
> x = src(0)
> for code in src:
> for i in range(1,code):
> if i == x:
> dst.append('\0')
> x = src(i)
> else:
> dst.append(i)
>
> dst.pop(0) #remove first byte
> # if code < 0xff
> # dst.append('\0')
>
>
>
>
> -mike
>
>
>
> --- Kent Johnson <[EMAIL PROTECTED]> wrote:
>
>
>>Michael Cotherman wrote:
>>
>>>def UnStuffData(src,dst,len):
>>>
>>> for code in src:
>>> for i in range(1,code):
>>> dst.append(i)
>>>
>>> if code < 0xff
>>> dst.append('\0')
>>>
>>>the above is the below code uncommented...
>>> it(and the original code) just seem to find the
>>
>>end
>>
>>>and puts a zero there...
>>>
>>>I do not see the existing zeroes replaced.....
>>
>>this is
>>
>>>kinda why I wanted to start from the
>>
>>specification...
>>
>>The above is the decoding code, it does what you
>>describe below. It is adding the zeros back in, that
>>is the dst.append('\0')
>>
>>Kent
>>
>>
>>>decoding is:
>>>pop the first byte of the packet off and place
>>>subsequent bytes into the output until you get to
>>
>>the
>>
>>>byte pointed to by the popped byte. When you reach
>>>that byte, read its value as the new 'relative'
>>>pointer, and copy x00 to the output. Proceed as
>>
>>above,
>>
>>>placing bytes to the output until the relative
>>
>>pointer
>>
>>>is reached or the end of the packet occurrs.
>>>
>>>I guess I need to look if I wish for this part of
>>
>>the
>>
>>>program to handle the input as one big existing
>>>string, or work on it a byte at a time as it comes
>>
>>in.
>>
>>>
>>>
>>>-mike c
>>
>>_______________________________________________
>>Tutor maillist - Tutor@python.org
>>http://mail.python.org/mailman/listinfo/tutor
>>
>
>
>
>
>
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>
>
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