What is the retroactivity of a new rule of law?

Where a new rule of law has been stated, the retroactivity of that decision must be established by applying the following criteria: " '(a) the purpose to be served by the new standards, (b) the extent of the reliance by law enforcement authorities on the old standards, and (c) the effect on the administration of justice of a retroactive application of the new standards.' (Citation.)" (People v. Gainer (1977) 19 Cal.3d 835, 853, 139 Cal.Rptr. 861, 566 P.2d 997.)