			/*
			=========================================================================
			mRGBE (miniRGBE): reduced RGBE encoding of normalised RGB floats plus
			associated integer payload data. By default, this encoding consists of:

			- three signed 5-bit mantissas for each RGB colour channel,
			- a common 5-bit exponent,
			- and an associated 12-bit integer datum.

			However, this allocation can be modified within a 32-bit envelope if more
			precision is required by modifying mRGBE_MANTBITS, mRGBE_EXPBITS and
			mRGBE_DATABITS.

			The encoded float RGB tuples are assumed to lie in the range [-1, 1],
			with values in the interval [-mRGBE_MIN, mRGBE_MIN] clamped to 0, since
			these cannot be resolved. The encoded values are therefore normalised
			against a given normalisation factor (e.g. absolute maximum) in order to
			maximise the useful range.

			Roland Schregle (roland.schregle@{hslu.ch, gmail.com})
			(c) Lucerne University of Applied Sciences and Arts,
			supported by the Swiss National Science Foundation
			(SNSF #179067, "Light Fields for Spatio-Temporal Glare Assessment")
			=========================================================================

			$Id$
			*/


			#ifndef _mRGBE_H
			#define _mRGBE_H

			#include <stdint.h>


			/* Mantissa / exponent / payload data bits and their encoding ranges.
			NOTE: binary shifts can overflow if the number of bits is increased;
			in this case shifts must either be promoted to 64 bits (possibly at
			the expense of portability), or replaced by much slower pow(2, ..) */
			#define mRGBE_MANTBITS 5
			#define mRGBE_EXPBITS 5
			#define mRGBE_DATABITS 12

			/* Signed maximum for mantissa */
			#define mRGBE_MANTMAX (1L << (mRGBE_MANTBITS - 1))
			/* Absolute overflow limit for mantissa (sign flips if exceeded) */
			#define mRGBE_MANTOVF ((mRGBE_MANTMAX << 1) - 1)
			#define mRGBE_MIN (1.0 / (1L << (1 << mRGBE_EXPBITS)))
			#define mRGBE_MAX 1.0
			#define mRGBE_RANGE (mRGBE_MAX - mRGBE_MIN)
			#define mRGBE_DATAMAX ((1U << mRGBE_DATABITS) - 1)


			typedef union {
			struct {
			/* (mini)RGBE representation consisting of a 4-bit mantissa + sign
			* per RGB, a common 5-bit exponent, and a 12-bit payload data */
			unsigned red: mRGBE_MANTBITS,
			grn: mRGBE_MANTBITS,
			blu: mRGBE_MANTBITS,
			exp: mRGBE_EXPBITS,
			dat: mRGBE_DATABITS;
			};

			uint32_t all;
			} mRGBE;

			/* State for mRGBE encoding to offset and normalise floats in order to
			* optimally utilise the encoding range */
			typedef struct {
			double min [3], max [3], norm [3];
			} mRGBERange;


			mRGBERange mRGBEinit (mRGBERange range,
			double rgbMin [3], double rgbMax [3]
			);
			/* Initialise range state for mRGBEencode()/mRGBEdecode() with
			* the specified float input ranges [rgbMin, rgbMax] in _absolute_ values
			* per colour channel. This sets the offset and normalisation for the
			* encoding. */

			mRGBE mRGBEencode (double rgb [3], const mRGBERange *range, unsigned data);
			/* Encode signed float RGB tuple to mRGBE along with payload data. The
			* supplied range state must be previously initialised with mRGBEinit().
			* A warning is issued if rgb lies outside the initialised range. */

			unsigned mRGBEdecode (mRGBE mrgbe, const mRGBERange *range, double rgb [3]);
			/* Decode mRGBE, returning signed float RGB tuple in array rgb. The
			* associated payload data is decoded as return value. The supplied
			* range state must be previously initialised with mRGBEinit(). */
			#endif

RadiancePmap/mrgbe.h
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mrgbe.h
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