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Avoid errors in domain bounds check by checking before the transformation #37

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stevengj merged 2 commits into from
May 4, 2026
Merged

Avoid errors in domain bounds check by checking before the transformation #37

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8f205c3
Check domain bounds before [-1,+1] transformation to avoid edge error…
hersle May 4, 2026
eab9f36
Test domain bounds check for @fastmath-sensitive example
hersle May 4, 2026
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4 changes: 2 additions & 2 deletions src/eval.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -61,8 +61,8 @@ end
Evaluate the Chebyshev polynomial given by `interp` at the point `x`.
"""
@fastmath function (interp::ChebPoly{N})(x::SVector{N,<:Real}) where {N}
all(interp.lb .≤ x .≤ interp.ub) || throw(ArgumentError("$x not in domain $(interp.lb) to $(interp.ub)"))
x0 = @. (x - interp.lb) * 2 / (interp.ub - interp.lb) - 1
all(abs.(x0) .≤ 1) || throw(ArgumentError("$x not in domain $(interp.lb) to $(interp.ub)"))
return evaluate(x0, interp.coefs, Val{N}(), 1, length(interp.coefs))
end

Expand Down Expand Up @@ -145,8 +145,8 @@ giving the derivatives of each component. If `v` is a scalar, then `J`
is a 1-row matrix; in this case you may wish to call `chebgradient` instead.
"""
function chebjacobian(c::ChebPoly{N}, x::SVector{N,<:Real}) where {N}
all(c.lb .≤ x .≤ c.ub) || throw(ArgumentError("$x not in domain $(c.lb) to $(c.ub)"))
x0 = @. (x - c.lb) * 2 / (c.ub - c.lb) - 1
all(abs.(x0) .≤ 1) || throw(ArgumentError("$x not in domain $(c.lb) to $(c.ub)"))
v, J = Jevaluate(x0, c.coefs, Val{N}(), 1, length(c.coefs))
return v, J .* 2 ./ (c.ub .- c.lb)'
end
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8 changes: 8 additions & 0 deletions test/runtests.jl
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Expand Up @@ -169,3 +169,11 @@ end
@inferred FastChebInterp.droptol(rand(5,5), 0.0)
@inferred chebinterp(rand(5,5), (0,0), (1,1))
end

# https://github.com/JuliaMath/FastChebInterp.jl/issues/36
@testset "boundscheck sensitivity with fastmath" begin
x = chebpoints(50, 1.0, 100.0)
c = chebinterp(sin.(x), 1.0, 100.0)
@test all([c(100.0)] .== map(c, [100.0]))
@test all([c(100.0)] .≈ c.([100.0]))
end
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