#include <PrintEx.h>

PrintEx serial = Serial;

void setup() {
  Serial.begin(57600);
}

void loop() {
    char qf_buf[50] = "";

    ltostrqf(-987654321 , 5, qf_buf);
    
    serial.printf("Count up  : %s\n", ltostrqf(123456789, 3, qf_buf));
    serial.printf("Count down: %s\n", ltostrqf(987654321, 3, qf_buf));
    serial.printf("\n");

    delay(5000);
}

char*  ltostrqf(long int value, unsigned char prec, char *buff )
{
    char fmt[] = "%ld.%Xld";
    fmt[5]     = '0' + prec;
    
    long int divisor = 1; 
    while(prec--)
        divisor *= 10;

    sprintf(buff, fmt, value / divisor, abs(value % divisor));
    return buff;
}