Here's the best advice I can give:
The * operator works fine for synthesis with ieee.numeric_std.unsigned.
I think Mike Treseler is basically right. For simulation only,
On Sun, 21 Oct 2007 21:07:04 -0700, Amit <amit.ko...@gmail.com> wrote:
Regarding floating point multiplication in VHDL. Can I use the regular
* operator or should I use Adder for this matter?
I think Mike Treseler is basically right. For simulation only,
you can just use ordinary VHDL variables of type REAL, and
all the normal arithmetic operations are available. math_real
provides all the usual mathematical library functions. But
if you are trying to build hardware, it's quite likely that
you only *think* you need floating-point, and in fact you
would be at least as well served by fixed-point arithmetic,
which is only integer arithmetic in party dress.
If you really, really want floating-point hardware, there
are two quick answers:
(1) look at the new IEEE synthesisable packages (they've been
mentioned here many times);
(2) you need both + and *. Very roughly:
- add the two exponents, not forgetting to subtract the bias
value if you are using a biased-exponent representation;
- multiply together the two fractions
- normalize the fraction (possible 1-bit left shift) if
necessary; if so, decrement the exponent by 1
- throw away the unused less-significant bits of the fraction,
having first done the necessary rounding on the more
significant bits.
Oh, and there are the special cases for zero, and proper
handling of Not-A-Number inputs, and overflow, and
denormalization if the exponent underflows, and choice of
rounding mode, and remembering to handle the hidden units
bit if you're using any of the standard formats, and
correctly manipulating the sign bit, and...
See what I mean? You really DON'T want floating-point, do you?
--
Jonathan Bromley, Consultant
DOULOS - Developing Design Know-how
VHDL * Verilog * SystemC * e * Perl * Tcl/Tk * Project Services
Doulos Ltd., 22 Market Place, Ringwood, BH24 1AW, UK
jonathan.brom...@MYCOMPANY.comhttp://www.MYCOMPANY.com
The contents of this message may contain personal views which
are not the views of Doulos Ltd., unless specifically stated.
This is a CLUE.
On Mon, 22 Oct 2007 11:55:21 -0700,
Amit <amit.ko...@gmail.com> wrote:
I have 4 different books of vhdl and none of them has
talked about floating point multiplications.
This is a CLUE.
Almost NO-ONE needs FP, except CPU designers who must provide it
so that people can write software with it.
You have not yet convinced us that you need FP at all.
The IEEE-754 FP standard provides enough information so that
you could implement it (or parts of it) in VHDL, provided you
are a competent hardware designer. But YOU DON'T NEED TO BOTHER.
Spend your time, and learning effort, on something more useful.
Learn about fixed-point, which will be really useful to you if
you want to do any DSP, 3D graphics, machine control or other
numerically-intensive applications. Floating-point is for
software weenies who lack the wit to calculate in advance
what precision they need
--
Jonathan Bromley, Consultant
DOULOS - Developing Design Know-how
VHDL * Verilog * SystemC * e * Perl * Tcl/Tk * Project Services
Doulos Ltd., 22 Market Place, Ringwood, BH24 1AW, UK
jonathan.brom...@MYCOMPANY.comhttp://www.MYCOMPANY.com
The contents of this message may contain personal views which
are not the views of Doulos Ltd., unless specifically stated.
Try this:
Try this: