Function to convert IEEE-754 float into IBM float for GRIB

float_convert_for_grib.c

#include <endian.h>
#include <stdint.h>
#include <stdio.h>

uint32_t to_grib_float(float r) {
	union {
		float f;
		uint32_t i;
		char c[4];
	} r_input;
	uint32_t v;

	uint32_t m;
	uint32_t b;
	uint32_t a;

	uint32_t fin_i;

	r_input.f = r;
	v = r_input.i;

	m = (0x7F800000 & v) >> 23;
	b = 0x7FFFFF & v;

	if ( (0 != m) && (0 != b) ) {
		m++;
		b = b| 0x800000;

		a = m + 129;
		while (0 != (a & 0x3)) {
			b = (b >> 1) & 0x7FFFFF;
			a++;
		}
		a = a >> 2;
	}

	/* printf(">>> 0x%02X 0x%08X 0x%02X 0x%06X.\n", v, (0x80000000 & v), a, b); */

	fin_i = (0x80000000 & v) | ((a << 24) & 0x7F000000) | b;
	return htobe32(fin_i);
}

/* {{{ for testing */
int main(int argc, char **argv) {
	uint32_t v;

	v = to_grib_float(-118.625);
	printf("> 0x%08X.\n", v);

	return 0;
}
/* }}} for testing */