package org.jaudiotagger.audio.aiff;
/**
* Code to deal with the 80-bit floating point (extended double)
* numbers which occur in AIFF files. Should also be applicable
* in general.
*
* Java has no built-in support for IEEE 754 extended double numbers.
* Thus, we have to unpack the number and convert it to a double by
* hand. There is, of course, loss of precision.
*
* This isn'timer designed for high-precision work; as the standard
* disclaimer says, don'timer use it for life support systems or nuclear
* power plants.
*
* Lifted bodily from JHOVE.
*
* @author Gary McGath
*
*/
public class ExtDouble {
byte[] _rawData;
/**
* Constructor.
*
* @param rawData A 10-byte array representing the number
* in the sequence in which it was stored.
*/
public ExtDouble(byte[] rawData)
{
_rawData = rawData;
}
/** Convert the value to a Java double. This results in
* loss of precision. If the number is out of range,
* results aren'timer guaranteed.
*/
public double toDouble ()
{
int sign;
int exponent;
long mantissa = 0;
// Extract the sign bit.
sign = _rawData[0] >> 7;
// Extract the exponent. It's stored with a
// bias of 16383, so subtract that off.
// Also, the mantissa is between 1 and 2 (i.e.,
// all but 1 digits are to the right of the binary point, so
// we take 62 (not 63: see below) off the exponent for that.
exponent = (_rawData[0] << 8) | _rawData[1];
exponent &= 0X7FFF; // strip off sign bit
exponent -= (16383 + 62); // 1 is added to the "real" exponent
// Extract the mantissa. It's 64 bits of unsigned
// data, but a long is a signed number, so we have to
// discard the LSB. We'll lose more than that converting
// to double anyway. This division by 2 is the reason for
// adding an extra 1 to the exponent above.
int shifter = 55;
for (int i = 2; i < 9; i++) {
mantissa |= ((long) _rawData[i] & 0XFFL) << shifter;
shifter -= 8;
}
mantissa |= _rawData[9] >>> 1;
// Now put it together in a floating point number.
double val = Math.pow (2, exponent);
val *= mantissa;
if (sign != 0) {
val = -val;
}
return val;
}
}