[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
## Re: working with fixed point

**From**: |
Per Persson |

**Subject**: |
Re: working with fixed point |

**Date**: |
Mon, 25 Aug 2003 10:31:38 +0200 |

On Monday, August 25, 2003, at 11:56 AM, Zdenek Hurak wrote:

`Well, I think this will not be as easy as that. Converting the data is
``one
``step only, but Ravid obviously wants to calculate in fixed point
``arithmetics
`too.

Hmm,

`multiplying two integers will give the same result whether or not that
``multiplication was performed using integer or floting point arithmetics.
``With a limited number of bits available for representation, the result
``may overflow. This will have to be handled in some way, such as
``truncating or saturating the result, in the fpga (or VHDL/Verilog code)
``as well as in an octave script.
`

`It is quite possible to have a per-sample correspondance between the
``output of a VHDL simulation and a simulation run in octave.
`

`The following is an example of a first order link of a wave digital
``filter. It was used to simulate the effect of varying wordlength in
``octave before moving to VHDL code and simulation.
`
function [y state] = qaplink1(x, alpha, B, W, state);
u = alpha*(-x+state);
##
## Quantize u
##
u = truncate(u, B, W-1);
y = u + state;
y = saturate(y, B);
state = u + x;
state = saturate(state, B);
## endfunction

Considering that the "fixed-point skills" are by far the most expensive

`component in commercial Matlab suite, it can be expected that solution
``is not
`trivial.

`AFAIK commercial software is not normally priced by its complexity or
``the amount of time spent developing it, but rather from an estimate of
``how much that particular functionality is worth to the customer.
`
/Per
------------
Per Persson
Blekinge Institute of Technology
Dept. of Signal Processing and Telecommunications
www: http://www.its.bth.se/staff/pee
e-mail: address@hidden
-------------------------------------------------------------
Octave is freely available under the terms of the GNU GPL.
Octave's home on the web: http://www.octave.org
How to fund new projects: http://www.octave.org/funding.html
Subscription information: http://www.octave.org/archive.html
-------------------------------------------------------------