feat: better sub for [ZZ|QQ]Matrix

Author: fieker

src/matrix.jl

@@ -20,7 +20,30 @@ function sub(x::_MatTypes, r::AbstractUnitRange{Int}, c::AbstractUnitRange{Int})
   return deepcopy(view(x, r, c))
 end
 
-getindex(x::_MatTypes, r::AbstractUnitRange{Int}, c::AbstractUnitRange{Int}) = sub(x, r, c)
+# flint does not support windows with non-continuous row or column indices
+# we overload some specific types to not hit the AA fallback
+for T in [ZZMatrix, QQMatrix]
+  @eval begin
+    function sub(M::$T, r::AbstractVector{<:Integer}, c::AbstractVector{<:Integer})
+      N = zero_matrix(base_ring(M), length(r), length(c))
+      ii = 1
+      GC.@preserve M N begin
+        for i in r
+          jj = 1
+          for j in c
+            set!(mat_entry_ptr(N, ii, jj), mat_entry_ptr(M, i, j))
+            jj += 1
+          end
+          ii += 1
+        end
+      end
+      return N
+    end
+  end
+end
+
+# make x[r, c] sugar for sub(x, r, c)
+getindex(x::_MatTypes, r::AbstractVector{Int}, c::AbstractVector{Int}) = sub(x, r, c)
 
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 #