or more specifically, extracting the components of such numbers, or
assembling those numbers from their components.
Among other things, I want to grab the mantissa from a 64bit (IEEE784)
floating point number, i.e. the top 12 bits of a floating point number
(excluding the sign bit) and I want it inline without the overhead of a
function call, i.e. if it were legal, I would like to do the following:
inline proc rmantissa(r : real) : int
{
union ieee784 { var rv : real; var iv : int; };
var x : ieee784;
// copy the floating point number 'r' into 'x'
x.rv = r;
// grab the top 12 bits but strip off the sign bit
return (x.iv >> 52) & 0x7ff;
}
As Chapel enforces a PASCAL-style concept on unions which allows access to
only those fields that have data currently in them, my above codes causes
a run-time error. A C-style approach where the names are pretty much just
aliases for one another would not.
Is there workaround, and if so, what is it?
Once we have this, we can then write the 2 routines ...
inline proc ieee754unpack(var r : real) : (int, int, int)
&
inline proc ieee754pack(sign : int, exponent : int, mantissa : int) : real
which will respectively
unpack/split an IEEE754 floating point number into a sign,
exponent and mantissa, all three being returned as integers
the exponent in raw (or denormalized) form,
and
build an IEEE754 floating point number from a sign, exponent
and mantissa, all three being given/passed as integers with
the exponent being raw or de-normalized
as well as routines to just extract/replace the individual components.
There are obviously more things that one needs to do with IEEE754
numbers but I will leave it there for now.
Regards - Damian
Pacific Engineering Systems International, 277-279 Broadway, Glebe NSW 2037
Ph:+61-2-8571-0847 .. Fx:+61-2-9692-9623 | unsolicited email not wanted here
Views & opinions here are mine and not those of any past or present employer
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