digits.h

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#ifndef DIGITS_H
#define DIGITS_H

#include "macros.h"
#include "iterator.h"

#include <stdlib.h>
#include <math.h>

#ifdef DOXYGEN
namespace c::include::digits {
#endif

typedef struct digit_counter digit_counter;
struct digit_counter    {
    unsigned char *digits;
    size_t idx;
    IteratorTail(unsigned char, digit_counter)
};

static unsigned char advance_digit_counter(digit_counter *dc)   {
    IterationHead(dc);
    unsigned char ret = dc->digits[dc->idx--];
    dc->exhausted = (dc->idx == -1);
    return ret;
}

void free_digit_counter(digit_counter *dc)  {
    if (dc->digits != NULL) {
        free(dc->digits);
    }
}

digit_counter digits(uintmax_t n)  {
    const size_t digit_len = (size_t) ceil(log10((double) (n + 1)));
    digit_counter ret = IteratorInitHead(
        advance_digit_counter,
        AddDestructor(free_digit_counter),
        ExtendInit(digits, (unsigned char *) malloc(digit_len * sizeof(unsigned char))),
        ExtendInit(idx, digit_len - 1)
    );
    for (size_t i = 0; i < digit_len; i++)    {
        ret.digits[i] = n % 10;
        n /= 10;
    }
    return ret;
}


#ifdef DOXYGEN
};
#endif

#endif