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Induced by running this: printf '%s\n' Tye tye Ned bu nd > w codespell -w --summary --count -Iw $(git ls-files|grep -v gnulib) Summary: cvignore 1 declration 1 endianess 1 instad 1 intall 2 ouput 1 reenabled 1 repoducible 1 uncompressible1 * ChangeLog-2007: Fix typos. * NEWS: Likewise. * inflate.c: Likewise. * sample/sub.c: Likewise. * tests/reproducible: Likewise. Since the above changed NEWS, I must also do this: * cfg.mk (old_NEWS_hash): Update, to reflect recent NEWS correction. (exclude_file_name_regexp--sc_codespell): Ignore THANKS. (codespell_ignore_words_list): Exempt two false-positives.
90 lines
2.7 KiB
C
90 lines
2.7 KiB
C
/* sub.c not copyrighted (n) 1993 by Mark Adler */
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/* version 1.1 11 Jun 1993 */
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/* sub is a simple filter to preprocess a data file before compression.
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It can increase compression for data whose points tend to be close to
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the last point. The output is the difference of successive bytes of
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the input. The add filter is used to undo what sub does. This could
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be used on 8-bit sound or graphics data.
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sub can also take an argument to apply this to interleaved sets of
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bytes. For example, if the data are 16-bit sound samples, then you
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can use "sub 2" to take differences on the low-byte stream and the
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high-byte stream. (This gives nearly the same effect as subtracting
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the 16-bit values, but avoids the complexities of endianness of the
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data.) The concept extends to RGB image data (sub 3), 16-bit stereo
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data (sub 4), floating point data (sub 4 or sub 8), etc.
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add takes no options, since the number of interleaved byte streams
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is put in the first two bytes of the output stream for add to use
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(in little-endian format).
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Examples:
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sub < graph.vga | gzip -9 > graph.vga.sgz
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sub < phone.snd | gzip -9 > phone.snd.sgz
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sub 2 < audio.snd | gzip -9 > audio.snd.sgz
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sub 3 < picture.rgb | gzip -9 > picture.rgb.sgz
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sub 4 < stereo.snd | gzip -9 > stereo.snd.sgz
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sub 8 < double.data | gzip -9 > double.data.sgz
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To expand, use the reverse operation, as in:
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gunzip < double.data.sgz | add > double.data
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*/
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#include <config.h>
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#include <stdio.h>
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#include <stdlib.h>
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#define MAGIC1 'S' /* sub data */
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#define MAGIC2 26 /* ^Z */
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#define MAX_DIST 16384
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char a[MAX_DIST]; /* last byte buffer for up to MAX_DIST differences */
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int
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main (int argc, char **argv)
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{
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int n = 1; /* number of differences */
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int i; /* difference counter */
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int c; /* byte from input */
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int atoi(); /* (avoid including stdlib for portability) */
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/* process arguments */
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if (argc > 2)
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{
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fputs("sub: only one argument needed--# of differences\n", stderr);
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exit(EXIT_FAILURE);
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}
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if (argc > 1)
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n = atoi(argv[1]);
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if (n < 0) n = -n; /* tolerate "sub -2" */
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if (n == 0 || n > MAX_DIST) {
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fputs("sub: incorrect distance\n", stderr);
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exit(EXIT_FAILURE);
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}
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/* initialize last byte */
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i = n;
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do {
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a[--i] = 0;
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} while (i);
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/* write differenced data */
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putchar(MAGIC1); putchar(MAGIC2); /* magic word for add */
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putchar(n & 0xff); /* so add knows what to do */
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putchar((n>>8) & 0xff);
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while ((c = getchar()) != EOF)
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{
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putchar((c - a[i]) & 0xff); /* write difference */
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a[i++] = c; /* save last byte */
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if (i == n) /* cycle on n differences */
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i = 0;
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}
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exit(EXIT_SUCCESS);
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return 0; /* avoid warning */
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}
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