Avoid allocation when computing norm of MVector (#1131)

* Avoid allocation when computing norm of MVector

* fix test on Julia nightly

Author: mateuszbaran

Project.toml

@@ -1,6 +1,6 @@
 name = "StaticArrays"
 uuid = "90137ffa-7385-5640-81b9-e52037218182"
-version = "1.5.15"
+version = "1.5.16"
 
 [deps]
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"

src/linalg.jl

@@ -226,7 +226,7 @@ _inner_eltype(x::Number) = typeof(x)
 end
 
 @inline maxabs_nested(a::Number) = abs(a)
-function maxabs_nested(a::AbstractArray)
+@inline function maxabs_nested(a::AbstractArray)
     prod(size(a)) == 0 && (return _init_zero(a))
 
     m = maxabs_nested(a[1])

test/broadcast.jl

@@ -236,9 +236,7 @@ end
         @test @inferred(add_bc!(MMatrix(SA[10 20; 30 40]), (1,2))) ::MMatrix{2,2,Int} == SA[11 21; 32 42]
 
         # Tuples of SA
-        @test SA[1,2,3] .* (SA[1,0],) === SVector{3,SVector{2,Int}}(((1,0), (2,0), (3,0)))
-        # Unfortunately this case of nested broadcasting is not inferred
-        @test_broken @inferred(SA[1,2,3] .* (SA[1,0],))
+        @test (@inferred SA[1,2,3] .* (SA[1,0],)) === SVector{3,SVector{2,Int}}(((1,0), (2,0), (3,0)))
     end
 
     @testset "SDiagonal" begin

test/linalg.jl

@@ -10,6 +10,10 @@ Base.getindex(m::RotMat2, i::Int) = getindex(m.elements, i)
 # Rotation matrices must be unitary so `similar_type` has to return an SMatrix.
 StaticArrays.similar_type(::Union{RotMat2,Type{RotMat2}}) = SMatrix{2,2,Float64,4}
 
+Base.@kwdef mutable struct KPS4{S, T, P}
+    v_apparent::T =       zeros(S, 3)
+end
+
 @testset "Linear algebra" begin
 
     @testset "SArray as a (mathematical) vector space" begin
@@ -313,6 +317,25 @@ StaticArrays.similar_type(::Union{RotMat2,Type{RotMat2}}) = SMatrix{2,2,Float64,
         @test norm(SVector{0,Float64}()) isa Float64
         @test norm(SA[SVector{0,Int}(),SVector{0,Int}()]) isa float(Int)
         @test norm(SA[SVector{0,Int}(),SVector{0,Int}()]) == norm([Int[], Int[]])
+
+        # no allocation for MArray -- issue #1126
+
+        @inline function calc_particle_forces!(s, pos1, pos2)
+            segment = pos1 - pos2
+            norm1 = norm(segment)
+            unit_vector = segment / norm1
+        
+            v_app_perp = s.v_apparent - s.v_apparent ⋅ unit_vector * unit_vector
+            half_drag_force = norm(v_app_perp)
+            nothing
+        end
+        kps4 = KPS4{Float64, MVector{3, Float64}, 6+4+1}()
+        
+        pos1 = MVector{3, Float64}(1.0, 2.0, 3.0)
+        pos2 = MVector{3, Float64}(2.0, 3.0, 4.0)
+        calc_particle_forces!(kps4, pos1, pos2)
+        calc_particle_forces!(kps4, pos1, pos2)
+        @test (@allocated calc_particle_forces!(kps4, pos1, pos2)) == 0
     end
 
     @testset "trace" begin