> On 2021-03-10, at 18:21:11, Robin Vowels wrote: > > From: "Schmitt, Michael" > Sent: Thursday, March 11, 2021 10:26 AM > > >> I was taught long ago to add 1 to a register using LA r#,1(,r#) and to >> subtract 1 using BCTR r#,0. > >> Is the fastest way now to use AHI r#,1 and AHI r#,-1? > > LA and BCTR are good when you don't want to change the CC. > BCTR R,0 is specially good because it needs only 2 bytes. > LA is good fir small values. > "Small" means when you can tolerate truncation to 24 or 31 bits.
You can use LA to subtract 1 if you have a negative value in a base register, subject to the same limit. -- gil
