Refactor conv #5677

Job	Run time
apple (aarch64-apple-ios)	11m 40s
apple (aarch64-apple-darwin)	5m 15s
linux (raspbian)	13m 21s
linux (aarch64-unknown-linux-gnu)	12m 58s
linux (armv6vfp-unknown-linux-gnueabihf)	17m 33s
linux (armv7-unknown-linux-gnueabihf)	17m 20s
linux (aarch64-unknown-linux-musl)	12m 25s
linux (armv7-unknown-linux-musl)	17m 21s
linux (aarch64-linux-android)	7m 53s
linux (armv7-linux-androideabi)	7m 19s
linux (i686-linux-android)	6m 43s
linux (x86_64-linux-android)	7m 23s
linux (wasm32-unknown-unknown)	6m 18s
linux (wasm32-wasi)	6m 1s
	2h 29m 30s

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