Run-length encoding/C: Difference between revisions

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Also: In this implementation, '''string'''s are assumed to be null terminated. Hence cannot contain the ''null'' character as data.
Also: In this implementation, '''string'''s are assumed to be null terminated. Hence cannot contain the ''null'' character as data.
<lang c>#include <stdio.h>
<syntaxhighlight lang="c">#include <stdio.h>
#include <stdlib.h>
#include <stdlib.h>
#include <string.h>
#include <string.h>
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printf("\n");
printf("\n");
return 0;
return 0;
}</lang>
}</syntaxhighlight>
Output:
Output:
<pre>
<pre>
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Since repeat counter must fit a single byte in this implementation, it can't be greater than 255, so a byte repeated more than 255 times generates in the compressed stream more than 2 bytes (4 bytes if the length of the repeated byte sequence is less than 511 and so on)
Since repeat counter must fit a single byte in this implementation, it can't be greater than 255, so a byte repeated more than 255 times generates in the compressed stream more than 2 bytes (4 bytes if the length of the repeated byte sequence is less than 511 and so on)


<syntaxhighlight lang="c">
<lang c>int rle_encode(char *out, const char *in, int l)
int rle_encode(char *out, const char *in, int l)
{
{
int dl, i;
int dl, i;
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*out++ = i; *out++ = cp; dl += 2;
*out++ = i; *out++ = cp; dl += 2;
return dl;
return dl;
}
}</lang>
</syntaxhighlight>


'''Decoding function'''
'''Decoding function'''


<syntaxhighlight lang="c">
<lang c>int rle_decode(char *out, const char *in, int l)
int rle_decode(char *out, const char *in, int l)
{
{
int i, j, tb;
int i, j, tb;
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}
}
return tb;
return tb;
}
}</lang>
</syntaxhighlight>


'''Usage example'''
'''Usage example'''


<lang c>#include <stdio.h>
<syntaxhighlight lang="c">#include <stdio.h>
#include <stdlib.h>
#include <stdlib.h>
#include <string.h>
#include <string.h>
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free(d); free(oc);
free(d); free(oc);
return 0;
return 0;
}
}</lang>
</syntaxhighlight>


In the following codes, encoding and decoding are implemented as "filters" which compress/decompress standard input to standard output writing ASCII strings; they will work as long as the input has no ASCII digits in it, and the compressed/original ratio of a "single group" will be less than or equal to 1 as long as the ASCII decimal representation's length of the repeat counter will be shorter than the length of the "group". It should be so except in the case the group is a single isolated character, e.g. B gives 1B (one byte against two compressed bytes)
In the following codes, encoding and decoding are implemented as "filters" which compress/decompress standard input to standard output writing ASCII strings; they will work as long as the input has no ASCII digits in it, and the compressed/original ratio of a "single group" will be less than or equal to 1 as long as the ASCII decimal representation's length of the repeat counter will be shorter than the length of the "group". It should be so except in the case the group is a single isolated character, e.g. B gives 1B (one byte against two compressed bytes)
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'''Encoding filter'''
'''Encoding filter'''


<syntaxhighlight lang="c">
<lang c>#include <stdio.h>
#include <stdio.h>


int main()
int main()
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printf("%d%c", i, cp);
printf("%d%c", i, cp);
return 0;
return 0;
}
}</lang>
</syntaxhighlight>


'''Decoding filter'''
'''Decoding filter'''


<syntaxhighlight lang="c">
<lang c>#include <stdio.h>
#include <stdio.h>


int main()
int main()
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}
}
return 0;
return 0;
}
}</lang>
</syntaxhighlight>


'''Final note''': since the repeat counter value 0 has no meaning, it could be used as it would be 256, so extending by one the maximum number of repetitions representable with a single byte; or instead it could be used as a special marker to encode in a more efficient way (long) sequences of ''isolated characters'', e.g. "ABCDE" would be encoded as "1A1B1C1D1E"; it could be instead encoded as "05ABCDE".
'''Final note''': since the repeat counter value 0 has no meaning, it could be used as it would be 256, so extending by one the maximum number of repetitions representable with a single byte; or instead it could be used as a special marker to encode in a more efficient way (long) sequences of ''isolated characters'', e.g. "ABCDE" would be encoded as "1A1B1C1D1E"; it could be instead encoded as "05ABCDE".
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