Integer to double conversion

Using Arduino Project Guidance
1

Hi everyone!

I am working on a project where I need to format raw bytes received via serial into float or double value. I am using Arduino mega for this project. I am able to convert into signed and unsigned integer but somehow conversion to float does not work. I am explaining my requirement below with an example :

Example :: 0x41CC28F6 should give 25.52

Below is the function I use for data conversion in my code.

void Format_Data(struct MB_RESP *input, unsigned char fmt, char *data)
{
  char arr[30];
  float real;
  unsigned long int temp;

  strcat(data, ",");
  switch (fmt)
  {
    case INT16:
      *((char*)(&temp) + 0) = input->data[1];
      *((char*)(&temp) + 1) = input->data[0];
      *((char*)(&temp) + 2) = 0;
      *((char*)(&temp) + 3) = 0;

      sprintf(arr, "%d", temp);
      arr[5] = '\0';
      strcat(data, arr);
      break;

    case UINT16:
      *((char*)(&temp) + 0) = input->data[1];
      *((char*)(&temp) + 1) = input->data[0];
      *((char*)(&temp) + 2) = 0;
      *((char*)(&temp) + 3) = 0;

      sprintf(arr, "%u", temp);
      arr[5] = '\0';
      strcat(data, arr);
      break;

    case INT32:
      *((char*)(&temp) + 0) = input->data[3];
      *((char*)(&temp) + 1) = input->data[2];
      *((char*)(&temp) + 2) = input->data[1];
      *((char*)(&temp) + 3) = input->data[0];

      sprintf(arr, "%ld", temp);
      arr[10] = '\0';
      strcat(data, arr);
      break;

    case UINT32:
      *((char*)(&temp) + 0) = input->data[3];
      *((char*)(&temp) + 1) = input->data[2];
      *((char*)(&temp) + 2) = input->data[1];
      *((char*)(&temp) + 3) = input->data[0];

      sprintf(arr, "%lu", temp);
      arr[10] = '\0';
      strcat(data, arr);
      break;

    case IEEE754FP:
      *((char*)(&temp) + 0) = input->data[1];
      *((char*)(&temp) + 1) = input->data[0];
      *((char*)(&temp) + 2) = input->data[3];
      *((char*)(&temp) + 3) = input->data[2];

      sprintf(arr, "%lu", temp);        //temporarily converting into unsigned long long int
    //   sprintf(arr, "%lf", (double)temp);     //gives '?' on serial
      arr[10] = '\0';
      strcat(data, arr);
      break;
  }
}

I have included all header files and there is no compilation error.

2

Hello

You can use memcpy, it's the safest way to do that

uint32_t d = 0x41CC28F6;
float f;
memcpy( &f, &d, sizeof(float) );
3

I see a problem with endian-ness. Or else you have typos in your array indices...

4

(double)temp does not work as you think it works. I'm not sure how to explain.

It does not take an integer and say that the bytes in it now represent a float; it takes the integer and says to treat it as a float.

5

I beg to differ

uint32_t value = 0x41CC28F6; // should give 25.52
char buff[20];
float tFloat = 999.666;

void setup() {
  Serial.begin(115200);
  Serial.print(F("casting 0x"));
  Serial.print(value, HEX);
  Serial.print(F(" to float gives "));
  dtostrf((float)value, 0, 6, buff);
  Serial.println(buff);
  Serial.print(F("interpreting 0x"));
  Serial.print(value, HEX);
  Serial.print(F(" as float "));
  memcpy(&tFloat, &value, sizeof(value));
  dtostrf(tFloat, 0, 6, buff);
  Serial.println(buff);
}

void loop() {}

casting 0x41CC28F6 to float gives 1103898900.000000
interpreting 0x41CC28F6 as float 25.520000
6

As I said, I'm not sure how to explain. But your code demonstrates what I wanted to convey.

7

I probably just misunderstood you. :grinning:

1 Like
8

This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.