#define _GNU_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

char *fcvt(double x, int n, int *dp, int *sign)
{
        char tmp[1500];
        int i, lz;

        if (n > 1400U) n = 1400;
        sprintf(tmp, "%.*f", n, x);
        i = (tmp[0] == '-');
        if (tmp[i] == '0') lz = strspn(tmp+i+2, "0");
        else lz = -(int)strcspn(tmp+i, ".");

        if (n<=lz) {
                *sign = i;
                *dp = 1;
                if (n>14U) n = 14;
                return "000000000000000"+14-n;
        }

        return ecvt(x, n-lz, dp, sign);
}