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faster min/max for IEEEFloats #45532

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faster min/max for IEEEFloats #45532

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7d38ef3
faster min/max for IEEEFloats
mikmoore May 31, 2022
de5d3b0
typo in comment
mikmoore Jun 1, 2022
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24 changes: 21 additions & 3 deletions base/math.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -765,9 +765,27 @@ max(x::T, y::T) where {T<:AbstractFloat} = ifelse((y > x) | (signbit(y) < signbi
min(x::T, y::T) where {T<:AbstractFloat} = ifelse((y < x) | (signbit(y) > signbit(x)),
ifelse(isnan(x), x, y), ifelse(isnan(y), y, x))

minmax(x::T, y::T) where {T<:AbstractFloat} =
ifelse(isnan(x) | isnan(y), ifelse(isnan(x), (x,x), (y,y)),
ifelse((y > x) | (signbit(x) > signbit(y)), (x,y), (y,x)))
function max(x::T, y::T) where {T<:IEEEFloat}
a = x > y ? x : y
b = y > x ? y : x
# if either argument is NaN, a != b and at least one is NaN
# else if they are opposite zeros, a == b and a !== b
# else a == b and a === b
argplus = a + b # a+b is NaN iff x or y is NaN or they are are opposite-signed Infs - opposite Infs are impossible given the preceding comparisons
argand = reinterpret(T, reinterpret(Unsigned, a) & reinterpret(Unsigned, b)) # no-op for a==b except to prefer +0.0 over -0.0
return isnan(argplus) ? argplus : argand
end

function min(x::T, y::T) where {T<:IEEEFloat}
a = x < y ? x : y
b = y < x ? y : x
# if either argument is NaN, a != b and at least one is NaN
# else if they are opposite zeros, a == b and a !== b
# else a == b and a === b
argplus = a + b # a+b is NaN iff x or y is NaN or they are are opposite-signed Infs - opposite Infs are impossible given the preceding comparisons
argor = reinterpret(T, reinterpret(Unsigned, a) | reinterpret(Unsigned, b)) # no-op for a==b except to prefer -0.0 over +0.0
return isnan(argplus) ? argplus : argor
end


"""
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2 changes: 1 addition & 1 deletion base/promotion.jl
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Expand Up @@ -487,6 +487,6 @@ minmax(x::Real) = (x, x)

max(x::T, y::T) where {T<:Real} = ifelse(y < x, x, y)
min(x::T, y::T) where {T<:Real} = ifelse(y < x, y, x)
minmax(x::T, y::T) where {T<:Real} = y < x ? (y, x) : (x, y)
minmax(x::T, y::T) where {T<:Real} = (min(x, y), max(x, y))

flipsign(x::T, y::T) where {T<:Signed} = no_op_err("flipsign", T)
4 changes: 2 additions & 2 deletions test/numbers.jl
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Expand Up @@ -104,8 +104,8 @@ end
@test minmax(-Inf, NaN) ≣ (NaN, NaN)
@test minmax(NaN, -Inf) ≣ (NaN, NaN)
@test minmax(NaN, NaN) ≣ (NaN, NaN)
@test min(-0.0,0.0) === min(0.0,-0.0)
@test max(-0.0,0.0) === max(0.0,-0.0)
@test min(-0.0,0.0) === min(0.0,-0.0) === -0.0
@test max(-0.0,0.0) === max(0.0,-0.0) === 0.0
@test minmax(-0.0,0.0) === minmax(0.0,-0.0)
@test max(-3.2, 5.1) == max(5.1, -3.2) == 5.1
@test min(-3.2, 5.1) == min(5.1, -3.2) == -3.2
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