> -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On > Behalf Of Charles Mills > Sent: Monday, October 23, 2006 10:17 AM > To: [email protected] > Subject: BCTR out of favor? > > While we're on the subject of machine performance . > > Do I recall correctly hearing that BCTR Rn,0 is no longer the favored way > of > decrementing a register, perhaps because the cache logic sees it as a > potential branch, and that AHI Rn,-1 should be substituted? > > Similarly, that AHI is preferable to LA for adding a small increment to a > register, perhaps because LA may invoke or "reserve" the address > translation > logic? > > Charles Mills
BCTR Rn,0 is alright for unsigned decrement. The branch target register is recognized as zero (never branch). I recommend always using LA when dealing with addresses. I prefer to use LA for small integer arithmetic. I don't use AHI much, but it has its place. Whatever you decide, be consistent and keep it simple for the next maintenance programmer. 2 cents worth. Your mileage may vary. Jeffrey D. Smith Principal Product Architect Farsight Systems Corporation 700 KEN PRATT BLVD. #204-159 LONGMONT, CO 80501-6452 303-774-9381 direct 303-484-6170 FAX http://www.farsight-systems.com/ comments are invited on my encryption project ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
