Father...
Very rarely smacked, if he did it was an arranged, organised 'at 5pm you get two smacks with the wooden spoon (giant thing he used for getting malt out for beer making) for doing xyz heinous crime'... And that was it, you knew why, you knew when and then it was done.
Would I repeat it, is it ok, no... however it was predictable and therefore avoidable, I got better at not getting caught!
Mother...
Smacked me in the face, knickers down smacks in public, would smack repeatedly without any understanding of why, or for crimes I had no understanding of, such as 'tone of voice' or 'back chat', abstract concepts a 2/3/4 year old really can't grasp. She was wildly unpredictable and could go from smiles and happy to lashing out in a second. You never knew when it'd stop and her cure for the hysterical gulping crying was to hold my head under the cold bath tap (which tells you how little I was that she could physically do that, I was a sturdy child), so that I'd either shut up or drown.
She was always significantly more dangerous if we were on our own with her, Father or other adults around and she was much less likely to lash out (though she could stew on something and lash out about it later when there were no witnesses).
She was an abuser, she is why for years, I would lash out physically, I knocked her on her arse at 14 and realised I outweighed her by a fair bit and could fight back (she immediately started a long running script about how she was the victim and I was the abuser, despite this happening once and once only!).
Neither type of smacking did me any good and it took a very long time for me to be able to control my own emotions, to not burst into tears at the slightest thing (that is returning, thanks Peri!). I still cannot stand conflict, I can't even watch shouty tv shows or video clips, even the totally staged ones where people get shouty at each other!