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Minimal fix for Algebraic Extensions over finite fields of order > 256. #1569

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Aug 8, 2017
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Minimal fix for Algebraic Extensions over finite fields of order > 256. #1569

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3edf1cb
Minimal fix forAlgebraic Extensions over finite fields of order > 256.
stevelinton Aug 5, 2017
b443aff
Add test for AlgebraicExtension over fields of size > 256
stevelinton Aug 5, 2017
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2 changes: 1 addition & 1 deletion lib/algfld.gi
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Expand Up @@ -105,7 +105,7 @@ local fam,i,cof,red,rchar,impattr,deg;
fam!.deg:=deg;
i:=List([1..DegreeOfLaurentPolynomial(p)],i->fam!.zeroCoefficient);
i[2]:=fam!.oneCoefficient;
i:=ImmutableVector(rchar,i,true);
i:=ImmutableVector(Size(f),i,true);
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This fix looks correct to me.

Nitpick on the commits: The message "Add test for this bug." is not so helpful. I'd either squash the two commits into one, or amend the commit message, say to "Add test for bug in AlgebraicExtension"

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Also: If you add Fixes #1561 or Resolves #1561 to the commit message (say as its last line), then merging this PR will automatically close #1561.

fam!.primitiveElm:=MakeImmutable(ObjByExtRep(fam,i));
fam!.indeterminateName:=MakeImmutable("a");

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14 changes: 14 additions & 0 deletions tst/testbugfix/2017-08-05-algfld.tst
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@@ -0,0 +1,14 @@
#
# AlgebraicExtension used to fail for finite fields of size over 256
#
gap> algexttest := function(q, i1, i2)
> local f,x,pol;
> f := GF(q);
> x :=Indeterminate(f,"x");
> pol := x^2+Z(q)^i1*x+Z(q)^i2;
> AlgebraicExtension(f,pol);
> end;;
gap> algexttest(1009,108,864); # from bug report
gap> algexttest(1024,1023,5); # prime under 256, field size over
gap> algexttest(65537,1,1); # prime over 2^16
gap> algexttest(3^11,1,6); # prime under 2^16, field over