1 files changed, 111 insertions, 0 deletions

diff --git a/xdelta3/badcopy.c b/xdelta3/badcopy.c
new file mode 100755
index 0000000..c42e2b5
--- /dev/null
+++ b/xdelta3/badcopy.c
@@ -0,0 +1,111 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h>
+
+#define BUFSZ (1 << 22)
+
+typedef unsigned int usize_t;
+
+double error_prob   = 0.0001;
+usize_t mean_change  = 100;
+usize_t total_change = 0;
+usize_t total_size   = 0;
+usize_t max_change   = 0;
+usize_t num_change   = 0;
+
+int last_end = 0;
+
+static int
+edist (usize_t mean, usize_t max)
+{
+  double mean_d = mean;
+  double erand  = log (1.0 / drand48 ());
+  usize_t x = (usize_t) (mean_d * erand + 0.5);
+
+  return (x < max) ? (x > 0 ? x : 1) : max;
+}
+
+void modify (char *buf, usize_t size)
+{
+  usize_t bufpos = 0, j;
+
+  last_end = 0;
+
+  for (;; /* bufpos and j are incremented in the inner loop */)
+    {
+      /* The size of the next modification. */
+      usize_t next_size = edist (mean_change, 1 << 31);
+      /* The expected interval of such a change. */
+      double expect_interval = ((double) next_size * (1.0 - error_prob)) / error_prob;
+      /* The number of bytes until the next modification. */
+      usize_t next_mod  = edist (expect_interval, 1 << 31);
+
+      if (next_size + next_mod + bufpos > size) { break; }
+
+      if (max_change < next_size) { max_change = next_size; }
+
+      bufpos += next_mod;
+
+      fprintf (stderr, "COPY: %u-%u (%u)\n", total_size + last_end, total_size + bufpos, bufpos - last_end);
+
+      fprintf (stderr, "ADD:  %u-%u (%u) is change %u\n", total_size + bufpos , total_size + bufpos + next_size, next_size, num_change);
+
+      total_change += next_size;
+      num_change   += 1;
+
+      for (j = 0; j < next_size; j += 1, bufpos += 1)
+        {
+          buf[bufpos] = lrand48 () >> 3;
+        }
+
+      last_end = bufpos;
+    }
+
+  fprintf (stderr, "COPY: %u-%u (%u)\n", total_size + last_end, total_size + size, size - last_end);
+
+  total_size += size;
+}
+
+int main(int argc, char **argv)
+{
+  char buf[BUFSZ];
+  int c, ret;
+
+  if (argc > 3)
+    {
+      fprintf (stderr, "usage: badcopy [byte_error_prob [mean_error_size]]\n");
+      return 1;
+    }
+
+  if (argc > 2) { mean_change = atoi (argv[2]); }
+  if (argc > 1) { error_prob  = atof (argv[1]); }
+
+  if (error_prob < 0.0 || error_prob > 1.0)
+    {
+      fprintf (stderr, "warning: error probability out of range\n");
+      return 1;
+    }
+
+  do
+    {
+      c = fread (buf, 1, BUFSZ, stdin);
+
+      if (c == 0) { break; }
+
+      modify (buf, c);
+
+      ret = fwrite (buf, 1, c, stdout);
+    }
+  while (c == BUFSZ);
+
+  if ((ret = fclose (stdout)))
+    {
+      perror ("fclose");
+      return 1;
+    }
+
+  fprintf (stderr, "add_prob %f; %u adds; total_change %u of %u bytes; add percentage %f; max add size %u\n",
+           error_prob, num_change, total_change, total_size, (double) total_change / (double) total_size, max_change);
+
+  return 0;
+}