On Mon, 28 Apr 2025 12:26:00 -0400, Phil Smith III wrote: >Ok, well, in 1975 I was still in high school and playing games on VM over >dialup, didn't start my mainframe career until 1980. But the question stands: >what's with these "unpreferred" values? Why would they even exist/be valid? > I suspect it's a holdover from parsimoniously engineered hardware. 1401? Punched cards? Competing vendors? ...? Only two nybble values should have been designated valid; any others should have caused data checks. but them gates was expensive back then. And doing it right nowadays wouldn't be compatible.
On Mon, 28 Apr 2025 16:32:40 +0000, Schmitt, Michael wrote: > ... >C: positive >D: negative >F: unsigned > ??? So is any unsigned number algebraically greater than any negative number, and algebraically less than any positive number? >If all your code has preferred signs then it can generate more efficient code, >by using CLC and MVC for example instead of packed decimal instructions. > Isn't the sign nybble in the rightmost byte, and doesn't CLC go left-to-right? I don't see how CLC can give correct results. I remember only vaguely, and from distant past the JCL converter failed my job on a decimal data exception on data it had generated. -- gil ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
