/*
 *  upkg: tool for manipulating Unreal Tournament packages.
 *  Copyright © 2012, 2020 Nick Bowler
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program 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 General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <config.h>
#include <math.h>

#include <uobject/uobject.h>
#include "pack.h"

/*
 * Deserialize an IEEE 754 binary32 value in "little endian" (for whatever
 * that term is worth in this context).  That is, when interpreted as a little
 * endian 32-bit unsigned integer: bit 31 is the sign, bits 30-23 are the
 * (biased) exponent, and bits 22-0 are the encoded part of the significand.
 *
 * The implementation is designed to be agnostic of the platform's actual
 * float type, but the conversion may be lossy if "float" is not itself a
 * binary32 format.  NaN payloads are not preserved.
 */
float u_unpack_binary32_le(const unsigned char *buf)
{
	unsigned long raw;
	long significand;
	int exponent;
	float result;

	raw = unpack_32_le(buf);
	exponent = (raw & 0x7f800000) >> 23;
	significand = (raw & 0x007fffff) >> 0;

	switch (exponent) {
	case 255:
		result = significand ? NAN : INFINITY;
		break;
	default:
		significand |= 0x00800000;
		/* fall through */
	case 0:
		result = ldexpf(significand, exponent-126-24);
	}

	return copysignf(result, raw & 0x80000000 ? -1 : 1);
}