Suppose a text file contains ASCII characters ‘0’ and ‘1’ representing bits in human readable form. For example, test.txt may contain 111111110000000 which means its size is 16 bytes. A simple method for compressing the file by a factor of 8 is to represent a block of 8 ‘0’ or ‘1’ ASCII characters as a single byte. Thus test.txt which is 16 bytes long can be compressed into a file that is 2 bytes long where the first byte contains all 1’s and the second byte all 0’s. The resultant compressed file is a binary file since the first byte is not an ASCII character.
Code an app, bitpacker, that reads from stdin the input filename which follows the same specification as Problem 3. However, instead of using getchar(), use the library function fgets() whose the second argument allows specifying how many bytes, at most, should be read which helps prevent array overrun. Process the data in the input file 8 characters at a time by reading them into a 1-D array, char rawdat[8]. Compact the eight ‘0’ and ‘1’ characters in rawdat[] into a single byte using the bit processing techniques discussed in class. Write the resultant byte into an output file with suffix “.P”. For the above example, test.txt.P. We will allow the size of the input file not to be a multiple of 8. Since we are compacting 8 ASCII characters ‘0’ and ‘1’ into a single byte, we will use padding to handle files whose size is not a multiple of 8. For example, if text file test1.dat contains characters 1111111100000000111 (file size is 19 bytes), we will pad the last three characters 111 with 00000 so that the byte containing bit values 11100000 is written to test1.dat.P. To note that we padded the original data with five 0 bit values, we will change the suffix of the output file to test1.dat.P5. For test.txt where no padding was needed, the output filename will be test.txt.P0. Thus the last character of the filename specifies how much padding (0-7) was added.
Code bitpacker as a single main() function. Test and verify that it works correctly.
