From 01430cae54294868432132f8f31be92056c04aa9 Mon Sep 17 00:00:00 2001
From: Simon Byrne <simonbyrne@gmail.com>
Date: Tue, 16 Jan 2018 14:09:40 -0800
Subject: [PATCH] Add reduce_empty definitions for bitwise ops on integers (&,
 | and xor)

---
 base/reduce.jl | 6 ++++++
 test/reduce.jl | 8 +++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/base/reduce.jl b/base/reduce.jl
index 811798e6651e6..4ee44b3739556 100644
--- a/base/reduce.jl
+++ b/base/reduce.jl
@@ -269,6 +269,12 @@ reduce_empty(::typeof(add_sum), ::Type{T}) where {T<:SmallUnsigned} = zero(UInt)
 reduce_empty(::typeof(mul_prod), T) = reduce_empty(*, T)
 reduce_empty(::typeof(mul_prod), ::Type{T}) where {T<:SmallSigned}  = one(Int)
 reduce_empty(::typeof(mul_prod), ::Type{T}) where {T<:SmallUnsigned} = one(UInt)
+reduce_empty(::typeof(&), ::Type{Bool}) = true
+reduce_empty(::typeof(&), ::Type{T}) where {T<:Integer} = -1 % T
+reduce_empty(::typeof(|), ::Type{Bool}) = false
+reduce_empty(::typeof(|), ::Type{T}) where {T<:Integer} = zero(T)
+reduce_empty(::typeof(xor), ::Type{Bool}) = false
+reduce_empty(::typeof(xor), ::Type{T}) where {T<:Integer} = zero(T)
 
 """
     Base.mapreduce_empty(f, op, T)
diff --git a/test/reduce.jl b/test/reduce.jl
index 66ac705fab643..0b44d87f58099 100644
--- a/test/reduce.jl
+++ b/test/reduce.jl
@@ -7,6 +7,12 @@ using Random
 @test foldl(+, Int16[]) === Int16(0) # In reference to issues #21536
 @test foldl(-, 1:5) == -13
 @test foldl(-, 10, 1:5) == -5
+@test foldl(&, UInt8[]) === typemax(UInt8)
+@test foldl(&, Int8[])  === Int8(-1)
+@test foldl(|, UInt8[]) === zero(UInt8)
+@test foldl(|, Int8[])  === zero(Int8)
+@test foldl(⊻, UInt8[]) === zero(UInt8)
+@test foldl(⊻, Int8[])  === zero(Int8)
 
 @test Base.mapfoldl(abs2, -, 2:5) == -46
 @test Base.mapfoldl(abs2, -, 10, 2:5) == -44
@@ -392,7 +398,7 @@ test18695(r) = sum( t^2 for t in r )
 
 # test neutral element not picked incorrectly for &, |
 @test @inferred(foldl(&, Int[1])) === 1
-@test_throws ArgumentError foldl(&, Int[])
+@test foldl(&, Int[]) === -1
 
 # prod on Chars
 @test prod(Char[]) == ""