/*
 *      I R C W 0 R M - N I C K G E N . C
 *      ---------------------------------
 *
 * source fragment of ircw0rm C++ source code, from
 * <a href="http://pastebin.ca/154650">original</a>
 *
 * provided by drnez on #hackphreak
 * updates, comments and analysis by grkvlt
 * updated: 01h22, friday 15 september 2006
 */

/*
 * the algorithm produces a random string of both lower- and
 * upper-case letters and optionally numbers. the distribution
 * of letters is as follows (in 1/15ths):
 *
 *      [aAzZ]   0   0.0%
 *      [b-n]    6  40.0%
 *      [o-y]    4  26.7%
 *      [B-G]    2  13.3%
 *      [H-Y]    3  20.0%
 *
 * also, there is a skew in the distribution due to the fact 
 * that MAX_INT is not divisible by 90, so the first MAX_INT % 90
 * characters are more likely to appear with a probability
 * of 1 / (MAX_INT / 90) or 0.13% approximately, over the rest
 * of the alphabet. this is pretty insignificant compared to the
 * distribution percentages above.
 *
 * additionally, if at any time 60 is produced as a random number,
 * the string will be truncated (if it is zero-filled) or will retain
 * the initial value for that character position. this occurs 1 / 90
 * or 1.1% of the time, and is not accounted for in the table above.
 *
 * whether the distributions are useful is another matter. it 
 * is easy to show that a nick does *not* conform to this pattern,
 * just loom for '[aAzZ]' anywhere. to prove that a string has
 * the same distribution with just eight samples (characters)
 * will be very error-prone, and requires more statistics-fu than
 * i can remember at present, although it is an interesting
 * problem...!.
 *
 * note that the original fragment was C++ and this function and
 * associated test harness are in C. this should not affect the operation
 * of the algorithm or the output, but see comments below regarding
 * the seeding of the prng.
 */

/*
 * sample output below. note line four, where output is truncated after six
 * characters, since randn == 60 and the initial buffer is zero-filled, so
 * any skipped characters are interpreted as '\0' or end of string.
 *
 *        "TXJcwNvh"
 *        "NThRpOlJ"
 *        "kYIbtRSn"
 *        "hRrSPn"
 *        "sgqcBTGq"
 *        "ijmLTTgs"
 *        "dkmtiOks"
 *
 */

/*
 * standard include files and definition of BOOL type for C
 */
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

typedef int BOOL;
#define TRUE (1 == 1)
#define FALSE (1 == 0)

/*
 * generate a random string of characters
 */
void RandomString(char *dst, int len, BOOL Gen_Numbers) {
    int i = 0, randn = 0;

    do {
        /* gen random number between 0 and 90 */
        randn = (rand() % 90);

        if (randn < 30 && i!=0 && Gen_Numbers == TRUE) {
            dst[i] = (48 + (rand() % 9));   /* gen number */
        } else if (randn < 60) {
            dst[i] = (98 + (rand() % 24));  /* gen lower case letter */
        } else if (randn > 60) {
            dst[i] = (66 + (rand() % 24));  /* gen upper case letter */
        }

        i++; len--;
    } while (len != 0);

    dst[i] = (char)0; /* null terminate */
}

/*
 * exercise the RandomString function in an infinite loop, generating
 * a new random, 8-character letter-only, string each time round.
 * 
 * no error checking for calloc() or time() library calls.
 *
 * compile and run as:
 *      gcc ircw0rm-nickgen.c -o ircw0rm-nickgen
 *      ./ircw0rm-nickgen
 */
int main(int argc, char **argv) {
    char *buf; /* pointer to string buffer */

    /*
     * init random number generator with system time (in seconds). in
     * the original code, this was inside RandomString and used GetTickCount
     * which has millisecond resolution. since we call the function many
     * times a second, using time() to re-seed the prng each iteration would
     * just generate lots of duplicates until the next second, so simply
     * seed once per execution.
     */
    srand((int)time(NULL));

    /* infinite loop */
    while (TRUE) {
        buf = (char *)calloc(9, sizeof(char)); /* alloc 9 chars, zeroed */
        RandomString(buf, 8, FALSE); /* eight characters, no numbers */
        printf("\t\"%s\"\n", buf); /* output generated string in quotes */
        free(buf); /* free the buffer */
    }
}