> On 2019-11-27, at 11:24:20, Jonathan Scott wrote: > > Ref: Your note of Wed, 27 Nov 2019 13:16:33 -0500 > >> My point is that XA took away 7 bits that were used for various purposes. >> Taking all 8 wouldn't have been a lot more painful. >> >> sas > > Are you serious? > He's serious. During overlap in support I wrote code to run on both 370 and in AMODE 31 on XA.
> In contrast, many 24-bit programs could be updated to run in > 31-bit addressing mode without any change to the code, > especially once the data management macros such as GET and PUT > were modified toclean the branch address. > But to "clean the branch address" meant to set bits 1-7 to zero which required that all referenced objects and code reside below the line. And access methods in that day needed to be called from below the line. My bimodal code used BR ,0 do detect the entry AMODE, then set or clear bit 0 of the image of R14 in RSA; BSM to AMODE 24, then return selectively by BR or BSM depending on caller's AMODE. Ugh. -- gil
