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

char* ecvt(double x, int n, int* dp, int* sign) {
    static char buf[16];
    char tmp[32];
    int i, j;

    if (n - 1U > 15)
        n = 15;
    sprintf(tmp, "%.*e", n - 1, x);
    i = *sign = (tmp[0] == '-');
    for (j = 0; tmp[i] != 'e'; j += (tmp[i++] != '.'))
        buf[j] = tmp[i];
    buf[j] = 0;
    *dp = atoi(tmp + i + 1) + 1;

    return buf;
}