/*
 * genfile — generate a text file of N lines, each a random 10-character
 * alphanumeric string followed by a newline. Used by the fastwc benchmarks
 * (createtxt in std.sh) to build test data quickly; std.sh falls back to a
 * slow shell loop when this binary has not been built.
 *
 * usage: genfile <lines>
 */
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>

#define LINE_LEN 10
#define CHUNK (64 * 1024)

static const char alpha[] =
    "abcdefghijklmnopqrstuvwxyz"
    "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    "0123456789";
#define ALPHA_LEN (sizeof(alpha) - 1)

static uint64_t state;

static uint64_t next(void)
{
    state ^= state << 13;
    state ^= state >> 7;
    state ^= state << 17;
    return state;
}

int main(int argc, char **argv)
{
    long n;
    long i;
    int j;
    char buf[CHUNK];
    size_t used = 0;

    if (argc != 2) {
        fprintf(stderr, "usage: %s <lines>\n", argv[0]);
        return 2;
    }
    n = atol(argv[1]);
    if (n < 0) {
        fprintf(stderr, "genfile: invalid line count: %s\n", argv[1]);
        return 2;
    }

    /* seed from time + pid so each run produces fresh data */
    state = (uint64_t)time(NULL) ^ ((uint64_t)getpid() << 32) ^ 0x9E3779B97F4A7C15ULL;

    for (i = 0; i < n; i++) {
        for (j = 0; j < LINE_LEN; j++)
            buf[used++] = alpha[next() % ALPHA_LEN];
        buf[used++] = '\n';
        if (used + LINE_LEN + 1 > CHUNK) {
            if (fwrite(buf, 1, used, stdout) != used)
                return 1;
            used = 0;
        }
    }
    if (used && fwrite(buf, 1, used, stdout) != used)
        return 1;
    if (fclose(stdout) != 0)
        return 1;
    return 0;
}