From 496bf99f9898a5d4e5256f90290303e89cc42f69 Mon Sep 17 00:00:00 2001
From: Fredrik Ekre <ekrefredrik@gmail.com>
Date: Fri, 22 Jul 2022 19:25:16 +0200
Subject: [PATCH] Implement zero(::HYPREVector) and copy!(::Vector,
 ::HYPREVector).

---
 src/HYPRE.jl     | 43 +++++++++++++++++++++++++++++++++++++++++++
 test/runtests.jl |  8 ++++++++
 2 files changed, 51 insertions(+)

diff --git a/src/HYPRE.jl b/src/HYPRE.jl
index 6219116..de6af4d 100644
--- a/src/HYPRE.jl
+++ b/src/HYPRE.jl
@@ -88,6 +88,39 @@ function Internals.assemble_vector(b::HYPREVector)
     return b
 end
 
+function Internals.get_proc_rows(b::HYPREVector)
+    jlower_ref = Ref{HYPRE_BigInt}()
+    jupper_ref = Ref{HYPRE_BigInt}()
+    @check HYPRE_IJVectorGetLocalRange(b.IJVector, jlower_ref, jupper_ref)
+    jlower = jlower_ref[]
+    jupper = jupper_ref[]
+    return jlower, jupper
+end
+
+function Internals.get_comm(b::HYPREVector)
+    # The MPI communicator is (currently) the first field of the struct:
+    # https://github.com/hypre-space/hypre/blob/48de53e675af0e23baf61caa73d89fd9f478f453/src/IJ_mv/IJ_vector.h#L23
+    # Fingers crossed this doesn't change!
+    @assert b.IJVector != C_NULL
+    comm = unsafe_load(Ptr{MPI.Comm}(b.IJVector))
+    return comm
+end
+
+function Base.zero(b::HYPREVector)
+    jlower, jupper = Internals.get_proc_rows(b)
+    comm = Internals.get_comm(b)
+    x = Internals.init_vector(comm, jlower, jupper)
+    # TODO All values 0 by default? Looks like it... Work in progress patch to hypre to
+    #      support IJVectorSetConstantValues analoguous to IJMatrixSetConstantValues.
+    nvalues = jupper - jlower + 1
+    indices = collect(HYPRE_BigInt, jlower:jupper)
+    values = zeros(HYPRE_Complex, nvalues)
+    @check HYPRE_IJVectorSetValues(x.IJVector, nvalues, indices, values)
+    # Finalize and return
+    Internals.assemble_vector(x)
+    return x
+end
+
 ######################################
 # SparseMatrixCS(C|R) -> HYPREMatrix #
 ######################################
@@ -194,6 +227,16 @@ function HYPREVector(x::Vector, ilower, iupper, comm=MPI.COMM_WORLD)
     return b
 end
 
+function Base.copy!(x::Vector, h::HYPREVector)
+    ilower, iupper = Internals.get_proc_rows(h)
+    nvalues = iupper - ilower + 1
+    if length(x) != nvalues
+        throw(ArgumentError("different lengths"))
+    end
+    indices = collect(HYPRE_BigInt, ilower:iupper)
+    @check HYPRE_IJVectorGetValues(h.IJVector, nvalues, indices, x)
+    return x
+end
 
 ##################################################
 # PartitionedArrays.PSparseMatrix -> HYPREMatrix #
diff --git a/test/runtests.jl b/test/runtests.jl
index ac1bc73..b8b0cc8 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -173,6 +173,14 @@ end
     Internals.assemble_vector(h)
     @test h.IJVector != HYPRE_IJVector(C_NULL)
     @test h.ParVector != HYPRE_ParVector(C_NULL)
+
+    # Base.zero(::HYPREVector) and Base.copy!(::Vector, HYPREVector)
+    b = rand(10)
+    h = HYPREVector(b, 1, 10)
+    z = zero(h)
+    b′ = copy!(b, z)
+    @test b === b′
+    @test iszero(b)
 end
 
 @testset "HYPREVector(::Vector)" begin