On Sat, 23 Oct 2021 11:33:33 -0500, Joe Monk wrote: > >I know this will probably be an easy answer for somebody... but I dont deal >with AM64 much. > AMD64? <https://en.wikipedia.org/wiki/X86-64>
>If Im in AM64 and I load an index register with -1, does the machine ignore >the sign when using it in an RX instruction such as STC? > >I know it ignores the sign in AM24/31... > I'm not familiar with the AMD64 architecture. But I know from experience that on the z, negative index values work better than many programmers expect or even believe, both at assembly time and in execution; in all addressing modes. Sign-magnitude architectures are relics of the past. The IBM 700/7000 series generally had sign-magnitude arithmetic but its index registers were twos complement. Negative indexes didn't work very well. The CDC 1604/3400/3600/3800 used ones complement arithmetic and twos complement indexes. The CDC 6400//6600 used both ones complement arithmetic and ones complement indexes. -- gil ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
