From: "John McKown" <john.archie.mck...@gmail.com> Sent: Thursday, March 12, 2015 1:49 AM
Given some of the new instructions, such as LGZR, I wish IBM would publish a manual with a title like: "What were the architects thinking of? Explanation of the reasons behind the instructions in the z architecture". Some are obvious, like L, ST, A. But why a single instruction to do this? Is it _that_ often used? And POPCNT is another one. Why do I need to know the number of 1 bits in each individual byte in a GPR?
Useful in some counting operations, where the bits represent a mask. Though not as a hardware instruction, it was used by about 1961 on DEUCE using an automatic shift operation. It was 15 times faster than the conventional way using a loop. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com
