Forth number formatting, ported to C

nfmt.c

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

#define NFMT_BUF_LEN 32

const char nfmt_set[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
char  nfmt_base;
char  nfmt_buf[NFMT_BUF_LEN+1] = {0};
char* nfmt_ptr;

// equivalent to BASE <# in Forth
void nfmt_init(char base) {
    nfmt_base = base;
    nfmt_buf[NFMT_BUF_LEN] = '\0';
    nfmt_ptr = &nfmt_buf[NFMT_BUF_LEN];
}

// equivalent to HOLD in Forth
void nfmt_hold(char c) {
    --nfmt_ptr;
    *nfmt_ptr = c;
}

// equivalent to HOLDS in Forth
void nfmt_holds(char* c) {
    int len = strlen(c);
    nfmt_ptr -= len;
    memcpy(nfmt_ptr, c, len);
}

// equivalent to # in Forth
void nfmt_digit(unsigned long* n) {
    char digit = nfmt_set[*n % nfmt_base];
    *n /= nfmt_base;
    nfmt_hold(digit);
}

// equivalent to #S in Forth
void nfmt_digits(unsigned long* n) {
    do {
        nfmt_digit(n);
    } while (*n != 0);
}

// equivalent to #> in Forth
char* nfmt_end() {
    return nfmt_ptr;
}


void thousands(unsigned long* n) {
    while (*n > 999) {
        nfmt_digit(n);
        nfmt_digit(n);
        nfmt_digit(n);
        nfmt_hold(',');
    }
    nfmt_digits(n);
}

char* number(long n) {
    char sign = 0;
    if (n < 0) {
        sign = 1;
        n = -n;
    }
    nfmt_init(10);
    thousands(&n);
    if (sign) nfmt_hold('-');
    return nfmt_end();
}

char* cents(long n) {
    char sign = 0;
    if (n < 0) {
        sign = 1;
        n = -n;
    }
    nfmt_init(10);
    if (sign) nfmt_hold(')'); // accounting-style negative numbers
    nfmt_digit(&n);
    nfmt_digit(&n);
    nfmt_hold('.');
    thousands(&n);
    nfmt_hold('$');
    if (sign) nfmt_hold('(');
    return nfmt_end();
}

char* hex(unsigned long n) {
    nfmt_init(16);
    nfmt_digits(&n);
    nfmt_holds("0x");
    return nfmt_end();
}

int main() {
    puts(number(25252));        // 25,252
    puts(number(-500));         // -500
    puts(cents(1234567890));    // $12,345,678.90
    puts(cents(-200000));       // ($2,000.00)
    puts(hex(32768));           // 0x8000
    puts(hex(-1));              // 0xFFFFFFFFFFFFFFFF
}