factors.h

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#ifndef DIVISORS_H
#define DIVISORS_H

#include "iterator.h"

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


typedef struct factor_counter factor_counter;
struct factor_counter   {
    uintmax_t target;
    uintmax_t current;
    IteratorTail(uintmax_t, factor_counter)
};

uintmax_t advance_factor_counter(factor_counter *fc);
inline uintmax_t advance_factor_counter(factor_counter *fc) {
    IterationHead(fc);
    while (fc->target > fc->current)   {
        fc->current++;
        if (fc->target % fc->current == 0)  {
            fc->exhausted = (fc->target == fc->current);
            return fc->current;
        }
    }
    return 0;
}

factor_counter proper_divisors(uintmax_t target);
inline factor_counter proper_divisors(uintmax_t target) {
    factor_counter ret = IteratorInitHead(advance_factor_counter, ExtendInit(target, target));
    return ret;
}

uintmax_t proper_divisor_count(uintmax_t target);
inline uintmax_t proper_divisor_count(uintmax_t target) {
    uintmax_t ret = 0;
    factor_counter fc = proper_divisors(target);
    while (!fc.exhausted)   {
        next(fc);
        ret++;
    }
    return ret;
}

#ifdef DOXYGEN
};
#endif

#endif