File r37/packages/factor/alphas.red artifact 1fb0a2812b part of check-in 12412d85b9

module alphas;

% Authors: A. C. Norman and P. M. A. Moore, 1981.

fluid '(alphalist current!-modulus hensel!-growth!-size
        number!-of!-factors);


%********************************************************************;
%
% This section contains access and update functions for the alphas.


symbolic procedure get!-alpha poly;
% Gets the poly and its associated alpha from the current alphalist
% if poly is not on the alphalist then we force an error.
  begin scalar w;
    w:=assoc!-alpha(poly,alphalist);
    if null w then errorf list("Alpha not found for ",poly," in ",
        alphalist);
    return w
  end;

symbolic procedure divide!-all!-alphas n;
% Multiply the factors by n mod p and alter the alphas accordingly.
  begin scalar om,m;
    om:=set!-modulus hensel!-growth!-size;
    m:=modular!-expt(
          modular!-reciprocal modular!-number n,
          number!-of!-factors #- 1);
    alphalist:=for each a in alphalist collect
      (times!-mod!-p(n,car a) . times!-mod!-p(m,cdr a));
    set!-modulus om
  end;

symbolic procedure multiply!-alphas(n,oldpoly,newpoly);
% Multiply all the alphas except the one associated with oldpoly
% by n mod p. also replace oldpoly by newpoly in the alphalist.
  begin scalar om,faca;
    om:=set!-modulus hensel!-growth!-size;
    n:=modular!-number n;
    oldpoly:=reduce!-mod!-p oldpoly;
    faca:=get!-alpha oldpoly;
    alphalist:=delete(faca,alphalist);
    alphalist:=for each a in alphalist collect
      car a . times!-mod!-p(cdr a,n);
    alphalist:=(reduce!-mod!-p newpoly . cdr faca) . alphalist;
    set!-modulus om
  end;

symbolic procedure multiply!-alphas!-recip(n,oldpoly,newpoly);
% Multiply all the alphas except the one associated with oldpoly
% by the reciprocal mod p of n. also replace oldpoly by newpoly.
  begin scalar om,w;
    om:=set!-modulus hensel!-growth!-size;
    n:=modular!-reciprocal modular!-number n;
    w:=multiply!-alphas(n,oldpoly,newpoly);
    set!-modulus om;
    return w
  end;

endmodule;

end;