1 files changed, 59 insertions, 0 deletions
diff --git a/sample/add.c b/sample/add.c
new file mode 100644
index 0000000..cadbc3a
--- /dev/null
+++ b/sample/add.c
@@ -0,0 +1,59 @@
+/* add.c   not copyrighted (n) 1993 by Mark Adler */
+/* version 1.1   11 Jun 1993 */
+
+/* This filter reverses the effect of the sub filter.  It requires no
+   arguments, since sub puts the information necessary for extraction
+   in the stream.  See sub.c for what the filtering is and what it's
+   good for. */
+
+#include <config.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#define MAGIC1    'S' /* sub data */
+#define MAGIC2    26  /* ^Z */
+#define MAX_DIST  16384
+
+char a[MAX_DIST];	/* last byte buffer for up to MAX_DIST differences */
+
+int main()
+{
+  int n;		/* number of differences */
+  int i;		/* difference counter */
+  int c;		/* byte from input */
+
+  /* check magic word */
+  if (getchar() != MAGIC1 || getchar() != MAGIC2)
+  {
+    fputs("add: input stream not made by sub\n", stderr);
+    exit(EXIT_FAILURE);
+  }
+
+  /* get number of differences from data */
+  if ((n = getchar()) == EOF || (i = getchar()) == EOF) {
+    fputs("add: unexpected end of file\n", stderr);
+    exit(EXIT_FAILURE);
+  }
+  n += (i<<8);
+  if (n <= 0 || n > MAX_DIST) {
+    fprintf(stderr, "add: incorrect distance %d\n", n);
+    exit(EXIT_FAILURE);
+  }
+
+  /* initialize last byte */
+  i = n;
+  do {
+    a[--i] = 0;
+  } while (i);
+
+  /* read differenced data and restore original */
+  while ((c = getchar()) != EOF)
+  {
+    c = (a[i++] += c) & 0xff;	/* restore data, save last byte */
+    putchar(c);			/* write original */
+    if (i == n)			/* cycle on n differences */
+      i = 0;
+  }
+  exit(EXIT_SUCCESS);
+  return 0;			/* avoid warning */
+}