Handling a quadruple precision floating point (128-bit) number in java

Question

I need to make use of numbers coming from another system that are 128-bit (quadruple-precision) floating point numbers in java.

Considering that there is no equivalent type in java, I would like to reduce the precision of the numbers using java code so they can be stored in a java double. This can be done fairly easily in c or using assembly but I would like to do it purely in java.

It is fair to assume that the quadruple-precision number is stored in a 128-bit byte array in java.

Is there a good solution, using only java? Thanks.

Answer 1

I was so intrigued by this question that I was compelled to write a library to handle IEEE-754 floating point numbers. With the library, you can use the following:

byte[] quadBytes; // your quad-floating point number in 16 bytes
IEEE754 quad = IEEE754.decode(IEEE754Format.QUADRUPLE, 
        BitUtils.wrapSource(quadBytes));
// IEEE754 holds the number in a 'lossless' format

From there, you can:

ByteBuffer doubleBuffer = ByteBuffer.allocateDirect(8);
quad.toBits(IEEE754Format.DOUBLE, BitUtils.wrapSink(doubleBuffer));
doubleBuffer.rewind();
double converted = doubleBuffer.asDoubleBuffer().get();

But the above snippet is just to illustrate general usage... a shorthand is provided for double:

double converted = quad.doubleValue();

The code is available at kerbaya.com/ieee754lib.

Answer 2

Depending on the size of the data set BigDecimal instantiated from an imported String representation might be an easy and accurate option. I assume one can export string representations of those numbers from any programming language.