Add abs(J) #637

Job	Run time
rust_ci (macos-latest, stable)	32s
rust_ci (ubuntu-latest, stable)	43s
rust_ci (ubuntu-latest, beta)	34s
rust_ci (windows-latest, beta)	47s
rust_ci (macos-latest, beta)	43s
rust_ci (windows-latest, stable)	38s
	3m 57s

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