What is the test for equal protection in the context of criminal convictions?

'The equal protection point almost answers itself. Surely it cannot be successfully urged that the difference between a conviction for a crime and a commitment for treatment is so insubstantial that any classification based upon such difference is arbitrary and has no substantial relation to the legitimate object of the legislation. (Baxstrom v. Harold, 383 U.S. 107, 111, 86 S.Ct. 760, 15 L.Ed.2d 620 ; Katzev v. County of Los Angeles, 52 Cal.2d 360, 368-370, 341 P.2d 310.)'

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