Collatz conjecture program in C, depends on libgmp

collatz.c

#include <stdio.h>
#include <string.h>
#include <gmp.h>

/*
 * Dependency: libgmp
 * Compile using:
 *          gcc -o collatz -l gmp collatz.c
 */

typedef enum { false, true } bool;
 
bool quiet;

void log_(unsigned long int count, mpz_t * number) {
    if (!quiet) {
        printf("%-8lu - \t", count);
        mpz_out_str(NULL, 10, *number);
        printf("\n");
    }
}

int main(int argc, char ** argv) {
    if (argc < 1) {
        printf("Argument required.\n");
        fflush(stdout);
        return 1;
    }
    int offset = 1;
    quiet = false;
    
    if (argc >= 2 && strcmp(argv[1], "--quiet") == 0) {
        offset++;
        quiet = true;
    }
    
    mpz_t number;
    mpz_init(number);
    
    mpz_set_str(number, argv[offset], 10);
    
    long int count = 0;
    
    log_(count, &number);
    
    mpz_t zero, one, tmp, tmp2;
    mpz_init(zero);
    mpz_init(one);
    mpz_set_si(one, 1);
    
    mpz_init(tmp);
    mpz_init(tmp2);
    
    if (mpz_cmp(number, zero) <= 0) {
        printf("Please enter a positive number, instead of %s\n", argv[offset]);
        fflush(stdout);
        return 2;
    }
    
    while (mpz_cmp(number, one) != 0) {
        count++;
        
        mpz_and(tmp, number, one);
        if (mpz_cmp(tmp, zero) == 0)
            mpz_fdiv_q_2exp(tmp, number, 1); // tmp := number >> 1 = number / 2
        else {
            mpz_mul_2exp(tmp2, number, 1); // tmp := number << 1 = 2 * number
            mpz_setbit(tmp2, 0); // tmp2 := tmp + 1 = 2 * number + 1
            mpz_add(tmp, tmp2, number); // tmp := tmp2 + number = 3 * number + 1
        }
        
        mpz_swap(number, tmp); // number := tmp
        
        log_(count, &number);
    }
    
    if (quiet)
        printf("%ld iterations needed\n", count);
    
    return 0;
}

test.sh

#!/bin/bash

if [ -z $DIGIT ]; then
	DIGIT=9
fi

repeat() {
	if [ $1 -eq 1 ]; then
		echo $DIGIT;
	elif [ $(( $1 % 2 )) -eq 0 ]; then
		local t=$(repeat $(($1 / 2)));
		echo $t$t
	else
		local t=$(repeat $(( ($1 - 1) / 2)));
		echo $DIGIT$t$t;
	fi
}


NB=$(repeat $1)
CHARS=$(echo $NB | wc -m)
CHARS=${CHARS/ /}
CHARS=$(( $CHARS - 1 )) # EOL is counted by wc ;)
echo $CHARS digits
time ./collatz --quiet $NB