From e4da59e96220b40c0196900338f3b9ed727bd4c1 Mon Sep 17 00:00:00 2001
From: Ziyi Yin <ziyi.yin@gatech.edu>
Date: Wed, 12 Apr 2023 11:25:29 -0400
Subject: [PATCH] add more comments

---
 ext/AbstractFFTsChainRulesCoreExt.jl | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/ext/AbstractFFTsChainRulesCoreExt.jl b/ext/AbstractFFTsChainRulesCoreExt.jl
index 119c079..016f347 100644
--- a/ext/AbstractFFTsChainRulesCoreExt.jl
+++ b/ext/AbstractFFTsChainRulesCoreExt.jl
@@ -33,10 +33,12 @@ function ChainRulesCore.rrule(::typeof(rfft), x::AbstractArray{<:Real}, dims)
     project_x = ChainRulesCore.ProjectTo(x)
     function rfft_pullback(ȳ)
         dY = ChainRulesCore.unthunk(ȳ)
-        # apply scaling
+        # apply scaling; below approach is for GPU CuArray compatibility, see PR #96
         dY_scaled = similar(dY)
         dY_scaled .= dY
         dY_scaled ./= 2
+        # assign view to a separate variable before assignment, to support Julia <1.2
+        # see https://github.com/JuliaLang/julia/issues/31295
         v = selectdim(dY_scaled, halfdim, 1)
         v .*= 2
         if 2 * (n - 1) == d
@@ -80,10 +82,12 @@ function ChainRulesCore.rrule(::typeof(irfft), x::AbstractArray, d::Int, dims)
     project_x = ChainRulesCore.ProjectTo(x)
     function irfft_pullback(ȳ)
         dX = rfft(real.(ChainRulesCore.unthunk(ȳ)), dims)
-        # apply scaling
+        # apply scaling; below approach is for GPU CuArray compatibility, see PR #96
         dX_scaled = similar(dX)
         dX_scaled .= dX
         dX_scaled .*= invN .* 2
+        # assign view to a separate variable before assignment, to support Julia <1.2
+        # see https://github.com/JuliaLang/julia/issues/31295
         v = selectdim(dX_scaled, halfdim, 1)
         v ./= 2
         if 2 * (n - 1) == d
@@ -125,10 +129,12 @@ function ChainRulesCore.rrule(::typeof(brfft), x::AbstractArray, d::Int, dims)
     project_x = ChainRulesCore.ProjectTo(x)
     function brfft_pullback(ȳ)
         dX = rfft(real.(ChainRulesCore.unthunk(ȳ)), dims)
-        # apply scaling
+        # apply scaling; below approach is for GPU CuArray compatibility, see PR #96
         dX_scaled = similar(dX)
         dX_scaled .= dX
         dX_scaled .*= 2
+        # assign view to a separate variable before assignment, to support Julia <1.2
+        # see https://github.com/JuliaLang/julia/issues/31295
         v = selectdim(dX_scaled, halfdim, 1)
         v ./= 2
         if 2 * (n - 1) == d