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#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;
}
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