dtostrf.c

/*
  dtostrf - Emulation for dtostrf function from avr-libc
  Copyright (c) 2013 Arduino.  All rights reserved.
  Written by Cristian Maglie <c.maglie@arduino.cc>

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public
  License along with this library; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>

char *dtostrf(double val, signed char width, unsigned char prec, char *sout)
{
  //Commented code is the original version
  /*char fmt[20];
  sprintf(fmt, "%%%d.%df", width, prec);
  sprintf(sout, fmt, val);
  return sout;*/

  // Handle negative numbers
  uint8_t negative = 0;
  if (val < 0.0) {
    negative = 1;
    val = -val;
  }

  // Round correctly so that print(1.999, 2) prints as "2.00"
  double rounding = 0.5;
  for (int i = 0; i < prec; ++i) {
    rounding /= 10.0;
  }

  val += rounding;

  // Extract the integer part of the number
  unsigned long int_part = (unsigned long)val;
  double remainder = val - (double)int_part;

  if (prec > 0) {
    // Extract digits from the remainder
    unsigned long dec_part = 0;
    double decade = 1.0;
    for (int i = 0; i < prec; i++) {
      decade *= 10.0;
    }
    remainder *= decade;
    dec_part = (int)remainder;

    if (negative) {
      sprintf(sout, "-%ld.%0*ld", int_part, prec, dec_part);
    } else {
      sprintf(sout, "%ld.%0*ld", int_part, prec, dec_part);
    }
  } else {
    if (negative) {
      sprintf(sout, "-%ld", int_part);
    } else {
      sprintf(sout, "%ld", int_part);
    }
  }
  // Handle minimum field width of the output string
  // width is signed value, negative for left adjustment.
  // Range -128,127
  char fmt[129] = "";
  unsigned int w = width;
  if (width < 0) {
    negative = 1;
    w = -width;
  } else {
    negative = 0;
  }

  if (strlen(sout) < w) {
    memset(fmt, ' ', 128);
    fmt[w - strlen(sout)] = '\0';
    if (negative == 0) {
      char *tmp = malloc(strlen(sout) + 1);
      strcpy(tmp, sout);
      strcpy(sout, fmt);
      strcat(sout, tmp);
      free(tmp);
    } else {
      // left adjustment
      strcat(sout, fmt);
    }
  }

  return sout;
}