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--- notes:discrete:fall2022:projects:rle1 [2022/09/29 15:23] – [PROGRAM] abarbcal
+++ notes:discrete:fall2022:projects:rle1 [2022/10/06 15:38] (current) – Added info about compression ratio. bolsen1
@@ Line 22: / Line 22: @@
 *For anybody interested in editing the wiki page, here is the dokuwiki user guide: https://www.dokuwiki.org/wiki:syntax#basic_text_formatting -Ash
-====CUSTOMIZATION: variable stride====
-=====PROGRAM=====
+=====DATA HEADER SPECIFICATIONS=====
+(mostly the same as rle0)
+Header Format:
+byte 0: 0x72\\
+byte 1: 0x6c\\
+byte 2: 0x65\\
+byte 3: 0x58\\
+byte 4: 0x20\\
+byte 5: 0x52\\
+byte 6: 0x4c\\
+byte 7: 0x45\\
+byte 8: 0x00 (reserved)\\
+byte 9: 0x02 (version)\\
+byte 10: 0x(stride value) -- changes depending on input\\
+byte 11: 0xArgv The length of the source file name, not including NULL terminator\\
+(how many characters in Argv - 1)\\
+byte 12: The name of the source file, not including the NULL terminator\\
+====CUSTOMISATION: variable stride====
+The stride will determine the workings of the the encoding/decoding process. In rle0, the stride was always 1, thus we had ababcc-> 1a1b1a1b2c, where we compressed runs of a single byte. For rle1, the stride given will determine how many bytes are in each run, for example a stride of two will mean we check for runs of two, which conducts as ababcc-> 2ab1cc. Since the strides are chars, they will hold any value between 1-255, and so each of these values should be valid for run length.
 =====PROGRAM=====
@@ Line 35: / Line 56: @@
 ./encode sample0.txt 2
 </cli>
-Encoder will output a file with the name of the original file appending a ''.lre'' at the end.
-Decode program will take two arguments:
+For ENCODE, the second argument no longer indicates the destination file name, the destination file name is provided by byte 12 of the header ( the name of the original file), and appending ''.rle'' at the end.
+For ENCODE, the second argument is now a STRIDE indicator, with a min of 0 and max of 255.
+No default stride, if no stride is indicated, display error. Store stride on byte 10 of the header.
+DECODE program will take only one argument, the encoded ''.rle'' file:
 <cli>
-./decode INFILE OUTFILE
+./decode INFILE
- argv[0] argv[1] argv[2]
+ argv[0] argv[1]
-./decode sample0.txt.rle sample0.txt
+./decode sample0.txt.rle
 </cli>
-The decoder should be able to read the header and find out the filename if a second argument is not given. If a second argument is given it will use the second argument instead of taking the filename from the header.
+The decoder should be able to read the header and find out the original filename. Decode will output a file with the name of the original file, without the ''.rle''.
-Decode will output a file of similar name without the .rle extension after running your decoder.
+The decoder should be able to read the header and find out the version of the encoded file. Depending on the version it should decode the provided file accordingly, making it backward-compatible.
+The decoder should be able to read the header and find out the stride and should decode the provided file accordingly.
 =====OUTPUT SPECIFICATIONS=====
+Just like what we did in rle0, the rle1's encoder should output the original file's length, the encoded file length, followed by the compression ratio. The output is not strict, as long as you have the correct input file length, output file length, and compression ratio. The compression ratio can be calculated by the following equation: 'Output Length / Input Length'. Make sure in your code to set the type of the variable holding the compression ratio to 'double' or 'float'. You may also want to take a look at the C output format specifiers for a prettier output.
+Example:
+         Input File length: 100
+         Output File length: 40
+         Compression ratio: .40 or 40%
 =====VERIFICATION=====
+**NOTE** Verification using ./check may not work. If this is the case, then run manual checks. To do this, run the sample and use the stride that is in the header of the sample output you are comparing to (Byte 10). The stride used is also in the file name.
+To run the check file provided to you when you grabbed the project, run ./check (linux-based system, may vary on different OS).
+You can also manually verify by encoding/decoding a file, and checking if it has the same md5sum as the file with or without the .rle extension depending on if you encoded or decoded. To do this, run your encoder/decoder, and enter md5sum (output file), again, linux-based system, may vary on a different OS.

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