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Mildly improve type-stability in chebyshev_clenshaw #628

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Mildly improve type-stability in chebyshev_clenshaw #628

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e324978
Mildly improve type-stability in chebyshev_clenshaw
jishnub Jan 31, 2024
5c23593
Fix return type
jishnub Feb 1, 2024
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10 changes: 5 additions & 5 deletions src/LinearAlgebra/clenshaw.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -217,20 +217,20 @@ sineshaw(c::AbstractVector,θ::AbstractMatrix) = promote_type(eltype(c),eltype(


function chebyshev_clenshaw(c::AbstractVector, x)
N,T = length(c),promote_type(eltype(c),typeof(x))
N,T = length(c),promote_type(eltype(c),float(typeof(x)))
if N == 0
return zero(float(x) * oneunit(eltype(c)))
return zero(T)
elseif N == 1 # avoid issues with NaN x
return first(c) * oneunit(float(x))
end

x = 2x
y = 2x
bk1,bk2 = zero(T),zero(T)
@inbounds for k = N:-1:2
bk2, bk1 = bk1, muladd(x,bk1,c[k]-bk2)
bk2, bk1 = bk1, muladd(y,bk1,c[k]-bk2)
end

muladd(x/2,bk1,c[1]-bk2)
muladd(x,bk1,c[1]-bk2)
end


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