Fix #28849: faster maximum, minimum (#30320)

base/reduce.jl

@@ -452,19 +452,63 @@ julia> prod(1:20)
 prod(a) = mapreduce(identity, mul_prod, a)
 
 ## maximum & minimum
+function _fast(::typeof(max),x,y)
+ ifelse(isnan(x),
+ x,
+ ifelse(x > y, x, y))
+end
+
+function _fast(::typeof(min),x,y)
+ ifelse(isnan(x),
+ x,
+ ifelse(x < y, x, y))
+end
+
+isbadzero(::typeof(max), x::AbstractFloat) = (x == zero(x)) & signbit(x)
+isbadzero(::typeof(min), x::AbstractFloat) = (x == zero(x)) & !signbit(x)
+isbadzero(op, x) = false
+isgoodzero(::typeof(max), x) = isbadzero(min, x)
+isgoodzero(::typeof(min), x) = isbadzero(max, x)
 
 function mapreduce_impl(f, op::Union{typeof(max), typeof(min)},
  A::AbstractArray, first::Int, last::Int)
- # locate the first non NaN number
- @inbounds a1 = A[first]
- v = mapreduce_first(f, op, a1)
- i = first + 1
- while (v == v) && (i <= last)
+ a1 = @inbounds A[first]
+ v1 = mapreduce_first(f, op, a1)
+ v2 = v3 = v4 = v1
+ chunk_len = 256
+ start = first
+ stop = start + chunk_len - 4
+ while stop <= last
+ isnan(v1) && return v1
+ isnan(v2) && return v2
+ isnan(v3) && return v3
+ isnan(v4) && return v4
+ @inbounds for i in start:4:stop
+ v1 = _fast(op, v1, f(A[i+1]))
+ v2 = _fast(op, v2, f(A[i+2]))
+ v3 = _fast(op, v3, f(A[i+3]))
+ v4 = _fast(op, v4, f(A[i+4]))
+ end
+ start = stop
+ stop = start + chunk_len - 4
+ end
+ v = op(op(v1,v2),op(v3,v4))
+ start += 1
+ for i in start:last
  @inbounds ai = A[i]
- v = op(v, f(ai))
- i += 1
+ v = op(v, f(A[i]))
  end
- v
+
+ # enforce correct order of 0.0 and -0.0
+ # e.g. maximum([0.0, -0.0]) === 0.0
+ # should hold
+ if isbadzero(op, v)
+ for i in first:last
+ x = @inbounds A[i]
+ isgoodzero(op,x) && return x
+ end
+ end
+ return v
 end
 
 maximum(f, a) = mapreduce(f, max, a)

test/reduce.jl

@@ -192,12 +192,55 @@ let x = [4,3,5,2]
  @test extrema(abs2, x) == (4, 25)
 end
 
+@test maximum([-0.,0.]) === 0.0
+@test maximum([0.,-0.]) === 0.0
+@test maximum([0.,-0.,0.]) === 0.0
+@test minimum([-0.,0.]) === -0.0
+@test minimum([0.,-0.]) === -0.0
+@test minimum([0.,-0.,0.]) === -0.0
+
+@testset "minimum/maximum checks all elements" begin
+ for N in [2:20;150;300]
+ for i in 1:N
+ arr = fill(0., N)
+ truth = rand()
+ arr[i] = truth
+ @test maximum(arr) == truth
+
+ truth = -rand()
+ arr[i] = truth
+ @test minimum(arr) == truth
+
+ arr[i] = NaN
+ @test isnan(maximum(arr))
+ @test isnan(minimum(arr))
+
+ arr = zeros(N)
+ @test minimum(arr) === 0.0
+ @test maximum(arr) === 0.0
+
+ arr[i] = -0.0
+ @test minimum(arr) === -0.0
+ @test maximum(arr) === 0.0
+
+ arr = -zeros(N)
+ @test minimum(arr) === -0.0
+ @test maximum(arr) === -0.0
+ arr[i] = 0.0
+ @test minimum(arr) === -0.0
+ @test maximum(arr) === 0.0
+ end
+ end
+end
+
 @test isnan(maximum([NaN]))
 @test isnan(minimum([NaN]))
 @test isequal(extrema([NaN]), (NaN, NaN))
 
 @test isnan(maximum([NaN, 2.]))
+@test isnan(maximum([2., NaN]))
 @test isnan(minimum([NaN, 2.]))
+@test isnan(minimum([2., NaN]))
 @test isequal(extrema([NaN, 2.]), (NaN,NaN))
 
 @test isnan(maximum([NaN, 2., 3.]))