simple float persistance to byte device

float-transmission.c

/* float-transmission.c: simple float persistance to byte device */
/* Copyright 2020 (C) Eric Herman */
/* License: WTFPL – Do What the Fuck You Want to Public License */
/* http://www.wtfpl.net */

/*
$ gcc -Wall -Wextra -o ./float-transmission ./float-transmission.c
$ ./float-transmission
sizeof(float) == 4
original      == 0.666667
bytes         == 0xabaa2a3f
round_trip    == 0.666667
do they match?   yes
*/

/* there are byte order issues to consider if going between machines of
 * different endian-ness, but not needed in our simple persistance case */


#include <stddef.h>

/* this is intentially verbose to make a clear example do it in fewer
 * lines in your own firmware */
void bytes_from_float(unsigned char *bytes, float f)
{
	float *fptr = NULL;
	unsigned char *fbytes = NULL;

	fptr = &f;
	fbytes = (unsigned char *)fptr;

	for (size_t i = 0; i < sizeof(float); ++i) {
		bytes[i] = fbytes[i];
	}
}

float float_from_bytes(unsigned char *bytes)
{
	float *fbytes = NULL;
	float f = 0.0;

	fbytes = (float *)bytes;
	f = *fbytes;

	return f;
}

#include <stdio.h>
int main(void)
{
	unsigned char float_byte_buffer[sizeof(float)];
	float original = 2.0 / 3.0;
	float round_trip = 0.0;

	printf("sizeof(float) == %zu\n", sizeof(float));
	printf("original      == %g\n", original);

	bytes_from_float(float_byte_buffer, original);
	printf("bytes         == 0x");
	for (size_t i = 0; i < sizeof(float); ++i) {
		printf("%02x", float_byte_buffer[i]);
	}
	printf("\n");

	round_trip = float_from_bytes(float_byte_buffer);
	printf("round_trip    == %g\n", round_trip);

	int error = (original != round_trip);

	printf("do they match?   %s\n", error ? "no" : "yes");

	return error;
}