/* decimal.c : PUBLIC DOMAIN - Jon Mayo - August 11, 2006
 * - You may remove any comments you wish, modify this code any way you wish,
 *   and distribute any way you wish.*/
/* just in case you don't have sprintf/snprintf you can use this code. */

#include <assert.h>
#include <limits.h>
#include <stddef.h>

/* used to figure out how many digits we need */
static unsigned number_digits_10(unsigned long n) {
	/* this is a much better algorithm than this:
	 * see p219 of Hacker's Delight, Henry S. Warren, Jr. 
	 * ISBN 0-201-91465-4 */
	const unsigned long logtab[] = { /* not actually log10 for 0 */
		9, 99, 999, 9999, 99999UL, 999999UL, 9999999UL, 99999999UL,
		999999999UL,
#if ULONG_MAX > 9999999999
		/* 64-bit support */
		9999999999ULL, 99999999999ULL, 999999999999ULL, 9999999999999ULL,
		99999999999999ULL, 999999999999999ULL, 9999999999999999ULL,
		99999999999999999ULL, 999999999999999999ULL,
#endif
		 ULONG_MAX, 
	};
	int i;

	for(i=0;;i++) {
		if(n<=logtab[i]) return i+1;
	}
	assert(1 /* should never get here */);
	return 0;
}

void decimal_to_str(unsigned long n, char *buf, size_t max) {
	unsigned i, len;

	/* comparing 10 table items is usually faster than other methods like
	 * dividing or multiplying 10 times */
	len=number_digits_10(n);
	assert(len+1 < max); /* overflow */
	for(i=0;i<len;i++) {
		buf[len-1-i]="0123456789"[n%10];
		if(!n) break;
		n/=10;
	}
	buf[i]=0;
}

/* define to try the example code below */
#ifdef STAND_ALONE
#include <stdlib.h>
#include <stdio.h>

/* just pass a list of filename to test this out on */
int main(int argc, char **argv) {
	unsigned long n;
	unsigned i;
	char buf[32];
	for(i=1;i<argc;i++) {
		n=strtoul(argv[i], 0, 0);
		decimal_to_str(n, buf, sizeof buf);
		printf("%s\n", buf);
	}
	return 0;
}
#endif