Converting double to float without relying on the FPU rounding mode

Question

Does anyone have handy the snippets of code to convert an IEEE 754 double to the immediately inferior (resp. superior) float, without changing or assuming anything about the FPU's current rounding mode?

Note: this constraint probably implies not using the FPU at all. I expect the simplest way to do it in these conditions is to read the bits of the double in a 64-bit long and to work with that.

You can assume the endianness of your choice for simplicity, and that the double in question is available through the d field of the union below:

union double_bits
{
  long i;
  double d;
};

I would try to do it myself but I am certain I would introduce hard-to-notice bugs for denormalized or negative numbers.

Answer 1

To do this job more accurately than just re-combine mantissa and exponent bit's check this out:

http://www.mathworks.com/matlabcentral/fileexchange/23173

regards