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Import finite field code from Hecke #2234

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9711057
Import finite field code from Hecke
fingolfin Jan 13, 2026
a678fbd
Transform ccall syntax
lgoettgens Jan 14, 2026
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80 changes: 77 additions & 3 deletions src/HeckeMiscFiniteField.jl
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Original file line number Diff line number Diff line change
@@ -1,6 +1,80 @@
# As of 14 May 2024:
# This is used in OSCAR, but requires (::fqPolyRepField)(::fpPolyRingElem)
# which is in Hecke
function (k::fqPolyRepField)(a::Vector{fpFieldElem})
return k(polynomial(Native.GF(Int(characteristic(k))), a))
end

###############################################################################

function _reduce(a::fqPolyRepFieldElem)
A = parent(a)
if a.length < 2*degree(A)
@ccall libflint.fq_nmod_reduce(a::Ref{fqPolyRepFieldElem}, A::Ref{fqPolyRepField})::Nothing
else
@ccall libflint.nmod_poly_rem(a::Ref{fqPolyRepFieldElem}, a::Ref{fqPolyRepFieldElem}, (pointer_from_objref(A)+6*sizeof(Int) + sizeof(Ptr{Nothing}))::Ref{Nothing}, (pointer_from_objref(A)+sizeof(ZZRingElem))::Ref{Nothing})::Nothing
end
end

function _reduce(a::FqPolyRepFieldElem)
A = parent(a)
#if a.length < 2*degree(A)
@ccall libflint.fq_reduce(a::Ref{FqPolyRepFieldElem}, A::Ref{FqPolyRepField})::Nothing
#else
# @ccall libflint.fmpz_mod_poly_rem(a::Ref{FqPolyRepFieldElem}, a::Ref{FqPolyRepFieldElem}, (pointer_from_objref(A)+6*sizeof(Int) + 2*sizeof(Ptr{Nothing}))::Ref{Nothing}, (pointer_from_objref(A)+sizeof(ZZRingElem))::Ref{Nothing})::Nothing
#end
end


#TODO: move elsewhere - and use. There are more calls to nmod_set/reduce
function (A::fqPolyRepField)(x::zzModPolyRingElem)
u = A()
@ccall libflint.fq_nmod_set(u::Ref{fqPolyRepFieldElem}, x::Ref{zzModPolyRingElem}, A::Ref{fqPolyRepField})::Nothing
_reduce(u)
return u
end

function (A::fqPolyRepField)(x::fpPolyRingElem)
u = A()
@ccall libflint.fq_nmod_set(u::Ref{fqPolyRepFieldElem}, x::Ref{fpPolyRingElem}, A::Ref{fqPolyRepField})::Nothing
_reduce(u)
return u
end

function _nf_to_fq!(a::fqPolyRepFieldElem, b::AbsSimpleNumFieldElem, K::fqPolyRepField, a_tmp::zzModPolyRingElem)
Nemo.nf_elem_to_nmod_poly!(a_tmp, b)
@ccall libflint.fq_nmod_set(a::Ref{fqPolyRepFieldElem}, a_tmp::Ref{zzModPolyRingElem}, K::Ref{fqPolyRepField})::Nothing
_reduce(a)
end

function _nf_to_fq!(a::fqPolyRepFieldElem, b::AbsSimpleNumFieldElem, K::fqPolyRepField, a_tmp::fpPolyRingElem)
Nemo.nf_elem_to_gfp_poly!(a_tmp, b)
@ccall libflint.fq_nmod_set(a::Ref{fqPolyRepFieldElem}, a_tmp::Ref{fpPolyRingElem}, K::Ref{fqPolyRepField})::Nothing
_reduce(a)
end

function _nf_to_fq!(a::FqPolyRepFieldElem, b::AbsSimpleNumFieldElem, K::FqPolyRepField, a_tmp::FpPolyRingElem)
Nemo.nf_elem_to_gfp_fmpz_poly!(a_tmp, b)
@ccall libflint.fq_set(a::Ref{FqPolyRepFieldElem}, a_tmp::Ref{FpPolyRingElem}, K::Ref{FqPolyRepField})::Nothing
_reduce(a)
end

function _nf_to_fq!(a::FqFieldElem, b::AbsSimpleNumFieldElem, K::FqField)#, a_tmp::FpPolyRingElem)
# AbsSimpleNumFieldElem -> QQPolyRingElem
z = QQPolyRingElem()
@ccall libflint.nf_elem_get_fmpq_poly(z::Ref{QQPolyRingElem}, b::Ref{AbsSimpleNumFieldElem}, parent(b)::Ref{AbsSimpleNumField})::Nothing
z.parent = Globals.Qx
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@lgoettgens lgoettgens Jan 14, 2026

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Globals.Qx does not exist in Nemo

# QQPolyRingElem -> ZZPolyRingElem, ZZRingElem
zz = ZZPolyRingElem()
@ccall libflint.fmpq_poly_get_numerator(zz::Ref{ZZPolyRingElem}, z::Ref{QQPolyRingElem})::Nothing
zz.parent = Globals.Zx
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Globals.Zx does not exist in Nemo

zzz = ZZRingElem()
@ccall libflint.fmpq_poly_get_denominator(zzz::Ref{ZZRingElem}, z::Ref{QQPolyRingElem})::Nothing
@ccall libflint.fq_default_set_fmpz_poly(a::Ref{FqFieldElem}, zz::Ref{ZZPolyRingElem}, K::Ref{FqField})::Nothing
# invert the denominator
c = characteristic(K)
@ccall libflint.fmpz_invmod(zzz::Ref{ZZRingElem}, zzz::Ref{ZZRingElem}, c::Ref{ZZRingElem})::Cint
@ccall libflint.fq_default_mul_fmpz(a::Ref{FqFieldElem}, a::Ref{FqFieldElem}, zzz::Ref{ZZRingElem}, K::Ref{FqField})::Nothing
#ccall((:fq_set, libflint), Nothing,
# (Ref{FqPolyRepFieldElem}, Ref{FpPolyRingElem}, Ref{FqPolyRepField}),
# a, a_tmp, K)
#_reduce(a)
return a
end
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