Rosetta Code

Run-length encoding/C: Difference between revisions

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Run-length encoding/C (view source)

Revision as of 07:43, 13 August 2023

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Also: In this implementation, '''string'''s are assumed to be null terminated. Hence cannot contain the ''null'' character as data.
<langsyntaxhighlight lang="c">#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
const char *input = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";
const char *output = "12W1B12W3B24W1B14W";
 
typedef void (*YIELDCHAR)(); /* yields via yield_init */
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#define YIELDS(type) BOOL (*yield)(type) = yield_init
 
ITERATOR gen_char_seq (const char *s){
YIELDS(char);
fflush(stdout);
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}
 
const char *zero2nine = "0123456789";
 
ITERATOR gen_decode (GENCHAR gen_char){
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}
 
int main(){
/* iterate through input string */
printf("Encode input: ");
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OD;
printf("\n");
return 0;
}</lang>
}</syntaxhighlight>
Output:
<pre>
Line 122 ⟶ 123:
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 dl, i;
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*out++ = i; *out++ = cp; dl += 2;
return dl;
}
}</lang>
</syntaxhighlight>
 
'''Decoding function'''
 
<syntaxhighlight lang="c">
<lang c>int rle_decode(char *out, const char *in, int l)
{
int i, j, tb;
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}
return tb;
}
}</lang>
</syntaxhighlight>
 
'''Usage example'''
 
<langsyntaxhighlight lang="c">#include <stdio.h>
#include <stdlib.h>
#include <string.h>
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int main()
{
char *d = (char *)malloc(2*strlen(o));
char *oc = (char *)malloc(strlen(o));
int rl = rle_encode(d, o, strlen(o));
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free(d); free(oc);
return 0;
}
}</lang>
</syntaxhighlight>
 
In the following codes, encoding and decoding are implementendimplemented 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)
 
'''Encoding filter'''
 
<syntaxhighlight lang="c">
<lang c>#include <stdio.h>
 
int main()
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}
printf("%d%c", i, cp);
return 0;
}</lang>
}
</syntaxhighlight>
 
'''Decoding filter'''
 
<syntaxhighlight lang="c">
<lang c>#include <stdio.h>
 
int main()
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for(j=0; j < i; j++) printf("%c", c);
}
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".
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