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Fix integer overflow in isapprox #50730

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merged 4 commits into from
Aug 14, 2023
Merged

Fix integer overflow in isapprox #50730

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26c2e88
Add tests for integer overflow with `isapprox`
nalimilan Jul 30, 2023
e2787ca
Fix integer overflow with `isapprox`
nalimilan Jul 30, 2023
3834ea0
Fix mixing integers and floats
nalimilan Jul 30, 2023
206ed68
Add trailing newline
nalimilan Jul 30, 2023
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15 changes: 14 additions & 1 deletion base/floatfuncs.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -304,7 +304,20 @@ true
function isapprox(x::Number, y::Number;
atol::Real=0, rtol::Real=rtoldefault(x,y,atol),
nans::Bool=false, norm::Function=abs)
x == y || (isfinite(x) && isfinite(y) && norm(x-y) <= max(atol, rtol*max(norm(x), norm(y)))) || (nans && isnan(x) && isnan(y))
x′, y′ = promote(x, y) # to avoid integer overflow
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If we have the other method, why do we need to widen here?

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@nalimilan nalimilan Jul 30, 2023 •
edited
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Because the other method is called only when both values are integer, but here norm(x) can overflow if x is an integer and y is a float. See tests added by the same commit.

EDIT: Note that the goal is not really to widen, but to switch to a floating point type so that instead of overflowing for values like typemax(Int8), norm gives a reasonable value to compute the tolerance.

x == y ||
(isfinite(x) && isfinite(y) && norm(x-y) <= max(atol, rtol*max(norm(x′), norm(y′)))) ||
Comment on lines +307 to +309
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Technically this can give slightly different results than before even in the absence of overflow, since promotion may round values larger than maxintfloat, giving a slightly different tolerance. But this should be OK.

(nans && isnan(x) && isnan(y))
end

function isapprox(x::Integer, y::Integer;
atol::Real=0, rtol::Real=rtoldefault(x,y,atol),
nans::Bool=false, norm::Function=abs)
if norm === abs && atol < 1 && rtol == 0
return x == y
else
return norm(x - y) <= max(atol, rtol*max(norm(x), norm(y)))
end
end

"""
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44 changes: 44 additions & 0 deletions test/floatfuncs.jl
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Expand Up @@ -209,3 +209,47 @@ end
struct CustomNumber <: Number end
@test !isnan(CustomNumber())
end

@testset "isapprox and integer overflow" begin
for T in (Int8, Int16, Int32)
T === Int && continue
@test !isapprox(typemin(T), T(0))
@test !isapprox(typemin(T), unsigned(T)(0))
@test !isapprox(typemin(T), 0)
@test !isapprox(typemin(T), T(0), atol=0.99)
@test !isapprox(typemin(T), unsigned(T)(0), atol=0.99)
@test !isapprox(typemin(T), 0, atol=0.99)
@test_broken !isapprox(typemin(T), T(0), atol=1)
@test_broken !isapprox(typemin(T), unsigned(T)(0), atol=1)
@test !isapprox(typemin(T), 0, atol=1)

@test !isapprox(typemin(T)+T(10), T(10))
@test !isapprox(typemin(T)+T(10), unsigned(T)(10))
@test !isapprox(typemin(T)+T(10), 10)
@test !isapprox(typemin(T)+T(10), T(10), atol=0.99)
@test !isapprox(typemin(T)+T(10), unsigned(T)(10), atol=0.99)
@test !isapprox(typemin(T)+T(10), 10, atol=0.99)
@test_broken !isapprox(typemin(T)+T(10), T(10), atol=1)
@test !isapprox(typemin(T)+T(10), unsigned(T)(10), atol=1)
@test !isapprox(typemin(T)+T(10), 10, atol=1)

@test isapprox(typemin(T), 0.0, rtol=1)
end
for T in (Int, Int64, Int128)
@test !isapprox(typemin(T), T(0))
@test !isapprox(typemin(T), unsigned(T)(0))
@test !isapprox(typemin(T), T(0), atol=0.99)
@test !isapprox(typemin(T), unsigned(T)(0), atol=0.99)
@test_broken !isapprox(typemin(T), T(0), atol=1)
@test_broken !isapprox(typemin(T), unsigned(T)(0), atol=1)

@test !isapprox(typemin(T)+T(10), T(10))
@test !isapprox(typemin(T)+T(10), unsigned(T)(10))
@test !isapprox(typemin(T)+T(10), T(10), atol=0.99)
@test !isapprox(typemin(T)+T(10), unsigned(T)(10), atol=0.99)
@test_broken !isapprox(typemin(T)+T(10), T(10), atol=1)
@test !isapprox(typemin(T)+T(10), unsigned(T)(10), atol=1)

@test isapprox(typemin(T), 0.0, rtol=1)
end
end