#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.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 (char*)"000000000000000" + 14 - n;
    }

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