Galois coerce QQ (#1149)

* Add coercion from fmpq to GaloisField.
Nemocas · Sep 6, 2021 · 5b37f25 · 5b37f25
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diff --git a/src/flint/gfp_elem.jl b/src/flint/gfp_elem.jl
@@ -402,6 +402,19 @@ function (R::GaloisField)(a::fmpz)
    return gfp_elem(d, R)
 end
 
+function (R::GaloisField)(a::fmpq)
+   num = numerator(a, false)
+   den = denominator(a, false)
+   n = ccall((:fmpz_fdiv_ui, libflint), UInt, (Ref{fmpz}, UInt),
+             num, R.n)
+   d = ccall((:fmpz_fdiv_ui, libflint), UInt, (Ref{fmpz}, UInt),
+             den, R.n)
+   V = [UInt(0)]
+   g = ccall((:n_gcdinv, libflint), UInt, (Ptr{UInt}, UInt, UInt), V, d, R.n)
+   g != 1 && error("Unable to coerce")
+   return R(n)*R(V[1])
+end
+
 function (R::GaloisField)(a::gfp_elem)
    return a
 end

diff --git a/test/flint/gfp-test.jl b/test/flint/gfp-test.jl
@@ -17,6 +17,10 @@
 
    @test isa(R(a), Nemo.gfp_elem)
 
+   @test isa(R(fmpq(7, 11)), Nemo.gfp_elem)
+   @test R(fmpq(7, 11))*11 == 7
+   @test_throws ErrorException R(fmpq(7, 13))
+
    for i = 1:1000
       p = rand(UInt(1):typemax(UInt))