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/*
* rpf.c: Conversion of float to reduced precision format values
*
* Written by: Stefan Frank
* Richard Krampfl
* Ullrich Hafner
*
* This file is part of FIASCO («F»ractal «I»mage «A»nd «S»equence «CO»dec)
* Copyright (C) 1994-2000 Ullrich Hafner <hafner@bigfoot.de>
*/
/*
* $Date: 2000/06/14 20:49:37 $
* $Author: hafner $
* $Revision: 5.1 $
* $State: Exp $
*/
#include "pm_config.h"
#include "config.h"
#include "mallocvar.h"
#include "types.h"
#include "macros.h"
#include "error.h"
#include "misc.h"
#include "rpf.h"
int const RPF_ZERO = -1;
/*****************************************************************************
private code
*****************************************************************************/
typedef struct {
double fraction;
int exponent;
} FracExp;
static FracExp
fracExpFromDouble(double const x) {
FracExp retval;
retval.fraction = frexp(x, &retval.exponent);
return retval;
}
int
rtob (real_t const f,
const rpf_t * const rpfP)
/*
* Convert real number 'f' into fixed point format.
* The real number in [-'range'; +'range'] is scaled to [-1 ; +1].
* Sign and the first 'precision' - 1 bits of the mantissa are
* packed into one integer.
*
* Return value:
* real value in reduced precision format
*/
{
/*
* Extract mantissa (23 Bits), exponent (8 Bits) and sign (1 Bit)
*/
double const normalized = f / rpfP->range;
/* 'f' scaled to [-1,+1] */
FracExp const fracExp = fracExpFromDouble(normalized);
unsigned int const signedMantissa =
(unsigned int) (fracExp.fraction * (1<<23));
unsigned int mantissa;
unsigned int sign; /* 0 for positive; 1 for negative */
if (signedMantissa < 0) {
mantissa = -signedMantissa;
sign = 1;
} else {
mantissa = +signedMantissa;
sign = 0;
}
/*
* Generate reduced precision mantissa.
*/
if (fracExp.exponent > 0)
mantissa <<= fracExp.exponent;
else
mantissa >>= -fracExp.exponent;
mantissa >>= (23 - rpfP->mantissa_bits - 1);
mantissa += 1; /* Round last bit. */
mantissa >>= 1;
if (mantissa == 0) /* close to zero */
return RPF_ZERO;
else if (mantissa >= (1U << rpfP->mantissa_bits)) /* overflow */
return sign;
else
return ((mantissa & ((1U << rpfP->mantissa_bits) - 1)) << 1) | sign;
}
float
btor (int const binary,
const rpf_t * const rpfP)
/*
* Convert value 'binary' in reduced precision format to a real value.
* For more information refer to function rtob() above.
*
* Return value:
* converted value
*/
{
unsigned int mantissa;
float sign;
float f;
if (binary == RPF_ZERO)
return 0;
if (binary < 0 || binary >= 1 << (rpfP->mantissa_bits + 1))
error ("Reduced precision format: value %d out of range.", binary);
/*
* Restore IEEE float format:
* mantissa (23 Bits), exponent (8 Bits) and sign (1 Bit)
*/
sign = (binary & 0x1) == 0 ? 1.0 : -1.0;
mantissa = (binary & ((0x1 << (rpfP->mantissa_bits + 1)) - 1)) >> 1;
mantissa <<= (23 - rpfP->mantissa_bits);
if (mantissa == 0)
f = sign;
else
f = sign * (float) mantissa / 8388608;
return f * rpfP->range; /* expand [ -1 ; +1 ] to
[ -range ; +range ] */
}
rpf_t *
alloc_rpf (unsigned const mantissa,
fiasco_rpf_range_e const range)
/*
* Reduced precision format constructor.
* Allocate memory for the rpf_t structure.
* Number of mantissa bits is given by `mantissa'.
* The range of the real values is in the interval [-`range', +`range'].
* In case of invalid parameters, a structure with default values is
* returned.
*
* Return value
* pointer to the new rpf structure
*/
{
rpf_t * rpfP;
MALLOCVAR(rpfP);
if (mantissa < 2) {
warning (_("Size of RPF mantissa has to be in the interval [2,8]. "
"Using minimum value 2.\n"));
rpfP->mantissa_bits = 2;
} else if (mantissa > 8) {
warning (_("Size of RPF mantissa has to be in the interval [2,8]. "
"Using maximum value 8.\n"));
rpfP->mantissa_bits = 2;
} else
rpfP->mantissa_bits = mantissa;
switch (range) {
case FIASCO_RPF_RANGE_0_75:
rpfP->range = 0.75;
rpfP->range_e = range;
break;
case FIASCO_RPF_RANGE_1_50:
rpfP->range = 1.50;
rpfP->range_e = range;
break;
case FIASCO_RPF_RANGE_2_00:
rpfP->range = 2.00;
rpfP->range_e = range;
break;
case FIASCO_RPF_RANGE_1_00:
rpfP->range = 1.00;
rpfP->range_e = range;
break;
default:
warning (_("Invalid RPF range specified. Using default value 1.0."));
rpfP->range = 1.00;
rpfP->range_e = FIASCO_RPF_RANGE_1_00;
break;
}
return rpfP;
}
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