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-- Copyright (C) 2002 Morgan Kaufmann Publishers, Inc
-- This file is part of VESTs (Vhdl tESTs).
-- VESTs is free software; you can redistribute it and/or modify it
-- under the terms of the GNU General Public License as published by the
-- Free Software Foundation; either version 2 of the License, or (at
-- your option) any later version.
-- VESTs is distributed in the hope that it will be useful, but WITHOUT
-- ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
-- FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
-- for more details.
-- You should have received a copy of the GNU General Public License
-- along with VESTs; if not, write to the Free Software Foundation,
-- Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
library ieee; use ieee.math_real.all;
package pwl_functions is
function pwl_dim1_extrap ( x : in real; xdata, ydata : in real_vector )
return real;
function interpolate (x,y2,y1,x2,x1 : in real)
return real;
function extrapolate (x,y2,y1,x2,x1 : in real)
return real;
end package pwl_functions;
package body pwl_functions is
-- code from book
function pwl_dim1_extrap ( x : in real; xdata, ydata : in real_vector )
return real is
variable xvalue, yvalue, m : real;
variable start, fin, mid: integer;
begin
if x <= xdata(0) then
yvalue := extrapolate ( x, ydata(1), ydata(0), xdata(1), xdata(0) );
return yvalue;
end if;
if x >= xdata(xdata'right) then
yvalue := extrapolate( x, ydata(ydata'right), ydata(ydata'right - 1),
xdata(xdata'right), xdata(xdata'right - 1) );
return yvalue;
end if;
start := 0;
fin := xdata'right;
while start <= fin loop
mid := (start + fin) / 2;
if xdata(mid) < x then
start := mid + 1;
else
fin := mid - 1;
end if;
end loop;
if xdata(mid) > x then
mid := mid - 1;
end if;
yvalue := interpolate( x, ydata(mid + 1), ydata(mid),
xdata(mid + 1), xdata(mid) );
return yvalue;
end function pwl_dim1_extrap;
-- end code from book
function interpolate (x,y2,y1,x2,x1 : in real)
return real is
variable m, yvalue : real;
begin
assert (x1 /= x2)
report "interpolate: x1 cannot be equal to x2"
severity error;
assert (x >= x1) and (x <= x2)
report "interpolate: x must be between x1 and x2, inclusively "
severity error;
m := (y2 - y1)/(x2 - x1);
yvalue := y1 + m*(x - x1);
return yvalue;
end function interpolate;
function extrapolate (x,y2,y1,x2,x1 : in real)
return real is
variable m, yvalue : real;
begin
assert (x1 /= x2)
report "extrapolate: x1 cannot be equal to x2"
severity error;
assert (x <= x1) or (x >= x2)
report "extrapolate: x is within x1, x2 bounds; interpolation will be performed"
severity warning;
m := (y2 - y1)/(x2 - x1);
yvalue := y1 + m*(x - x1);
return yvalue;
end function extrapolate;
end package body pwl_functions;
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