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taxidsim.c
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taxidsim.c
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/* Generate 10-digit random numbers and count whether generated number
makes a German tax id or not.
Elmar Klausmeier, 07-Jan-2013
*/
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
int myrand (void) {
static int m=0, r=0;
r = (m == 0) ? (int)random() : r/10;
m = (m + 1) % 8;
return (r % 10);
}
int main (int argc, char *argv[]) {
FILE *fp;
int prtflag = 0, taxflag = 0;
int c, i=0, t=0, l=10, x[10], g[10], r[10], rs[10];
long n0, n=5;
g[0] = 0;
g[1] = 0;
g[2] = 0;
g[3] = 0;
g[4] = 0;
g[5] = 0;
g[6] = 0;
g[7] = 0;
g[8] = 0;
g[9] = 0;
r[0] = 0;
r[1] = 0;
r[2] = 0;
r[3] = 0;
r[4] = 0;
r[5] = 0;
r[6] = 0;
r[7] = 0;
r[8] = 0;
r[9] = 0;
x[0] = -1;
x[1] = -1;
x[2] = -1;
x[3] = -1;
x[4] = -1;
x[5] = -1;
x[6] = -1;
x[7] = -1;
x[8] = -1;
x[9] = -1;
while ((c = getopt(argc,argv,"l:n:pt")) != -1) {
switch (c) {
case 'l':
l = atoi(optarg);
if (l < 3 || l > 10) {
printf("%s: limit l must be in [3...10]\n",argv[0]);
return 1;
}
break;
case 'n':
n = atol(optarg);
break;
case 'p':
prtflag = 1;
break;
case 't':
taxflag = 1;
break;
default:
printf("%s: unknown flag %c\n",argv[0],c);
return 2;
}
}
if ((fp = fopen("/dev/urandom","r")) == NULL) {
printf("%s: cannot open /dev/urandom, %s\n",
argv[0], strerror(errno));
return 3;
}
srandom(fgetc(fp) * 256 + fgetc(fp));
//n = (10 * n) / 2; // divide by 2, because we read two digits per byte
n0 = n;
n = l * n;
while (n-- > 0) {
//if ((c = fgetc(fp)) == EOF) break;
c = myrand();
//x[i] = ((c & 0xFF) >> 4) % 10;
//x[i+1] = (c & 0xFF) % 10;
//x[i] = ((c & 0xFF) >> 2) % 10;
x[i] = c % 10;
g[x[i]] += 1;
//g[x[i+1]] += 1;
r[x[i]] += 1;
//r[x[i+1]] += 1;
if (i+1 == l) {
rs[0] = 0;
rs[1] = 0;
rs[2] = 0;
rs[3] = 0;
rs[4] = 0;
rs[5] = 0;
rs[6] = 0;
rs[7] = 0;
rs[8] = 0;
rs[9] = 0;
rs[r[0]] += 1;
rs[r[1]] += 1;
rs[r[2]] += 1;
rs[r[3]] += 1;
rs[r[4]] += 1;
rs[r[5]] += 1;
rs[r[6]] += 1;
rs[r[7]] += 1;
rs[r[8]] += 1;
rs[r[9]] += 1;
t += c = (x[0] != 0 && rs[0] == 11-l && rs[1] == l-2 && rs[2] == 1);
if ((taxflag && c) || prtflag) printf("%c%d %d %d %d %d %d %d %d %d %d / %d%d%d%d%d%d%d%d%d%d\n",
c?'*':' ',x[0],x[1],x[2],x[3],x[4],x[5],x[6],x[7],x[8],x[9],
r[0],r[1],r[2],r[3],r[4],r[5],r[6],r[7],r[8],r[9]);
r[0] = 0;
r[1] = 0;
r[2] = 0;
r[3] = 0;
r[4] = 0;
r[5] = 0;
r[6] = 0;
r[7] = 0;
r[8] = 0;
r[9] = 0;
}
//i = (i + 2) % 10;
i = (i + 1) % l;
}
puts("Digit\tOccur.\tPerc.");
for (i=0; i<10; ++i)
printf("%d\t%d\t%f\n", i, g[i],100.0*g[i]/(l*n0));
printf("tax ids: %d\t%f\n", t, 100.0*t / n0);
if (fclose(fp) != 0) {
printf("%s: cannot close /dev/urandom, %s\n",
argv[0], strerror(errno));
return 4;
}
return 0;
}