fixup eval_op(ChiSq): do not repeat the formula

Author: alyst

src/metrics.jl

@@ -239,7 +239,7 @@ corr_dist(a::AbstractArray, b::AbstractArray) = evaluate(CorrDist(), a, b)
 result_type(::CorrDist, a::AbstractArray, b::AbstractArray) = result_type(CosineDist(), a, b)
 
 # ChiSqDist
-@inline eval_op(::ChiSqDist, ai, bi) = ifelse(ai != bi, abs2(ai - bi) / (ai + bi), zero(abs2(ai - bi) / (ai + bi)))
+@inline eval_op(::ChiSqDist, ai, bi) = (d = abs2(ai - bi) / (ai + bi); ifelse(ai != bi, d, zero(d)))
 @inline eval_reduce(::ChiSqDist, s1, s2) = s1 + s2
 chisq_dist(a::AbstractArray, b::AbstractArray) = evaluate(ChiSqDist(), a, b)