> -----Original Message----- > From: IBM Mainframe Assembler List > [mailto:[email protected]] On Behalf Of John Gilmore > Sent: Tuesday, December 27, 2011 4:55 PM > To: [email protected] > Subject: Re: Idea for a possible enhancement to z architecture > > John, > > The IBM 360/67 had such an instruction; and the verdict on it was > mixed, in part perhaps because its original implementation contained a > logic error. > > Look at the Compare Immediate and Trap, CIT and CGIT, instructions in > the z/Architecture PrOp. They are more general, but they can do what > you want to do. > > John Gilmore, Ashland, MA 01721 - USA
Well, yes, they can. If they are used. I know, when using HLASM, such is the responsibility of the programmer. I wonder if the C compiler emits such instructions before dereferencing a pointer. That was what prompted my thought - C pointer dereferencing of a NULL pointer. I wonder which would have more overhead: consistent use of the compare and trap (or compare plus branch, 2 instructions, or compare-and-branch instruction on the z196) or a hardware during execution test for a non-GPR0 base register containing a NULL pointer. Not that I'm likely to ever work for a company with current hardware again. -- John McKown Systems Engineer IV IT Administrative Services Group HealthMarkets(r) 9151 Boulevard 26 * N. Richland Hills * TX 76010 (817) 255-3225 phone * [email protected] * www.HealthMarkets.com Confidentiality Notice: This e-mail message may contain confidential or proprietary information. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies of the original message. HealthMarkets(r) is the brand name for products underwritten and issued by the insurance subsidiaries of HealthMarkets, Inc. -The Chesapeake Life Insurance Company(r), Mid-West National Life Insurance Company of TennesseeSM and The MEGA Life and Health Insurance Company.SM
