Fix generic mul accidental type promotion Int32 -> Int64 (#35164)

JuliaLang · Apr 11, 2020 · c8d277f · c8d277f
1 parent 1547522
commit c8d277f
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Showing 2 changed files with 11 additions and 4 deletions.
diff --git a/stdlib/LinearAlgebra/src/matmul.jl b/stdlib/LinearAlgebra/src/matmul.jl
@@ -649,7 +649,7 @@ function generic_matvecmul!(C::AbstractVector{R}, tA, A::AbstractVecOrMat, B::Ab
         for k = 1:mA
             aoffs = (k-1)*Astride
             if mB == 0
-                s = zero(R)
+                s = false
             else
                 s = zero(A[aoffs + 1]*B[1] + A[aoffs + 1]*B[1])
             end
@@ -662,7 +662,7 @@ function generic_matvecmul!(C::AbstractVector{R}, tA, A::AbstractVecOrMat, B::Ab
         for k = 1:mA
             aoffs = (k-1)*Astride
             if mB == 0
-                s = zero(R)
+                s = false
             else
                 s = zero(A[aoffs + 1]*B[1] + A[aoffs + 1]*B[1])
             end
@@ -676,14 +676,14 @@ function generic_matvecmul!(C::AbstractVector{R}, tA, A::AbstractVecOrMat, B::Ab
             if !iszero(_add.beta)
                 C[i] *= _add.beta
             elseif mB == 0
-                C[i] = zero(R)
+                C[i] = false
             else
                 C[i] = zero(A[i]*B[1] + A[i]*B[1])
             end
         end
         for k = 1:mB
             aoffs = (k-1)*Astride
-            b = _add(B[k], 0)
+            b = _add(B[k], false)
             for i = 1:mA
                 C[i] += A[aoffs + i] * b
             end

diff --git a/stdlib/LinearAlgebra/test/matmul.jl b/stdlib/LinearAlgebra/test/matmul.jl
@@ -394,6 +394,13 @@ end
     end
 end
 
+@testset "#35163" begin
+    # typemax(Int32) * Int32(1) + Int32(1) * Int32(1) should wrap around
+    # not promote to Int64, convert to Int32 and throw inexacterror
+    val = mul!(Int32[1], fill(typemax(Int32), 1, 1), Int32[1], Int32(1), Int32(1))
+    @test val[1] == typemin(Int32)
+end
+
 # Number types that lack conversion to the destination type
 struct RootInt
     i::Int