An initial sketch

Author: andrewjradcliffe

src/vfindextrema.jl

@@ -0,0 +1,49 @@
+#
+# Date created: 2022-06-22
+# Author: aradclif
+#
+#
+############################################################################################
+
+function vfindextrema(f::F, initmin::Iₘᵢₙ, initmax::Iₘₐₓ, A::AbstractArray{T, N}) where {F, Iₘᵢₙ, Iₘₐₓ, T, N}
+    Tₒ = Base.promote_op(f, T)
+    mn, mx = initmin(Tₒ), initmax(Tₒ)
+    i_mn, i_mx = firstindex(A), firstindex(A)
+    @turbo for i ∈ eachindex(A)
+        v = f(A[i])
+        newmin = v < mn
+        newmax = v > mx
+        i_mn = ifelse(newmin, i, i_mn)
+        i_mx = ifelse(newmax, i, i_mx)
+        mn = ifelse(newmin, v, mn)
+        mx = ifelse(newmax, v, mx)
+    end
+    ((mn, i_mn), (mx, i_mx))
+end
+vfindextrema(A) = vfindextrema(identity, typemax, typemin, A)
+vfindextrema(f, A) = vfindextrema(f, typemax, typemin, A)
+
+_rf_findextrema((((fm₁, im₁), (fx₁, ix₁))), (((fm₂, im₂), (fx₂, ix₂)))) =
+    ((Base.isgreater(fm₁, fm₂) ? (fm₂, im₂) : (fm₁, im₁)), (isless(fx₁, fx₂) ? (fx₂, ix₂) : (fx₁, ix₁)))
+findextrema(f, domain) = mapfoldl(((k, v),) -> ((f(v), k), (f(v), k)), _rf_findextrema, pairs(domain))
+findextrema(domain) = findextrema(identity, domain)
+
+vfindextrema2(A) = vfindmin(A), vfindmax(A)
+vfindextrema2(f, A) = vfindmin(f, A), vfindmax(f, A)
+
+@benchmark vfindextrema($x)
+@benchmark findextrema($x)
+findextrema(x)
+vfindextrema(x)
+@benchmark vfindmin($x)
+@benchmark vfindmax($x)
+for i = 1:20
+    for j = -1:1
+        N = (1 << i) + j
+        x = rand(N)
+        println("N = $N; vfindextrema (single pass):")
+        @btime vfindextrema($x)
+        println("N = $N; vfindextrema2 (two passes):")
+        @btime vfindextrema2($x)
+    end
+end