开云体育

Register Add - Quick Question

adriansutherland67 All Messages By This Member #1023 Is there a better way than this to add 8 to R1? ? ? ? ? ?LA? ? R0,8 ? ? ? ? ?AR? ? R1,R0? ? ? ? ? Add 8 to R1 Thanks A
Joe Monk All Messages By This Member #1024 Yes!? LA R1,8(R1) Joe toggle quoted message Show quoted text On Thu, Apr 16, 2020 at 1:09 PM adriansutherland67 <adrian@...> wrote: Is there a better way than this to add 8 to R1? ? ? ? ? ?LA? ? R0,8 ? ? ? ? ?AR? ? R1,R0? ? ? ? ? Add 8 to R1 Thanks A
Peter Coghlan All Messages By This Member #1025 Mostly! LA works as long as the answer fits in 24 bits so it's no good for adding 8 to a negative value in R1 for example. An alternative solution is: A R1,=F'8' If memory is really tight, you could use this and possibly save two bytes: AH R1,=H'8' Regards, Peter Coghlan. toggle quoted message Show quoted text Yes! LA R1,8(R1) Joe On Thu, Apr 16, 2020 at 1:09 PM adriansutherland67 < adrian@...> wrote: Is there a better way than this to add 8 to R1? LA R0,8 AR R1,R0 Add 8 to R1 Thanks A
Joe Monk All Messages By This Member #1026 This form of LA: LA Rx,D2(Rx)? is only good to add up to 4095 to a register. Past that you have to use other instructions. And as Peter noted, the left 8 bits will be zeroed in AM24. Joe toggle quoted message Show quoted text On Thu, Apr 16, 2020 at 1:30 PM Peter Coghlan <groups@...> wrote: Mostly! LA works as long as the answer fits in 24 bits so it's no good for adding 8 to a negative value in R1 for example. An alternative solution is: ? ? ? ? ?A? ? ?R1,=F'8' If memory is really tight, you could use this and possibly save two bytes: ? ? ? ? ?AH? ? R1,=H'8' Regards, Peter Coghlan. > > Yes! > > LA R1,8(R1) > > Joe > > > On Thu, Apr 16, 2020 at 1:09 PM adriansutherland67 < > adrian@...> wrote: > > > Is there a better way than this to add 8 to R1? > > > >? ? ? ? ? LA? ? R0,8 > >? ? ? ? ? AR? ? R1,R0? ? ? ? ? Add 8 to R1 > > > > Thanks A > > > > > > > >
adriansutherland67 All Messages By This Member #1027 You are gentlemen ... thank you! It is for a 24 bit address. A
adriansutherland67 All Messages By This Member #1028 On Thu, Apr 16, 2020 at 06:30 PM, Peter Coghlan wrote: save two bytes: AH R1,=H'8' Peter ... You have taught me what F meant!
Tony Harminc All Messages By This Member #1036 On Thu, 16 Apr 2020 at 14:56, adriansutherland67 <adrian@...> wrote: You are gentlemen ... thank you! It is for a 24 bit address. A couple of points... In modern (i.e. z) architectural variants, there are new immediate instructions that may help with this. Notably there is AHI (Add Halfword Immediate), which adds a 16-bit signed number from within the instruction to a register. These are not in S/370, but in practice they are in Hercules as a retrofitted feature. The topic of addressing arithmetic in S/370 and successors is worth becoming familiar with, and will probably help you understand why some things are done the way they are. Essentially this arithmetic is unsigned binary, with either one or two 32-bit register and one 12-bit immediate inputs, and an output that is either 24-bits (in original 370 24-bit mode) or 31-bits (in XA mode and above). It has also been extended to 64-bits in zArch (and the 12-bit input can be 20-bit in some instructions), but that's a larger change. Overflows are ignored. An interesting thing about this arithmetic is that, although it's unsigned, it can still subtract - this is a surprise to many people until they think about how twos complement number representation is defined. There is a whole section in the Principles of Operation on this. Higher end machine models typically had a separate addressing adder just for this purpose, since it is such a common operation. Tony H.
adriansutherland67 All Messages By This Member #1043 On Fri, Apr 17, 2020 at 05:04 PM, Tony Harminc wrote: immediate instructions It was the lack of these that freaked me out a bit! To be honest I am just doing the minimum in assembler before passing on to c where the heavy lifting is done. For example assembler can make a new frame up the stack and detect an overrun. Can flip to an auxiliary stack so it can call a C MORESTAK ... but C handles finding a new stack bin, etc. If folks are interested! :-)
James Oswald All Messages By This Member #4989 Regarding 24 bit addressing with 32 bit arithmetic. ?When addressing memory in 24 bit mode, only the low 24 bits of the 32 bit generated address are used. I worked in Poughkeepsie in the early '70s adding MP support to MVS. ?I can remember one incident when Kingston assembled the first fully configured 168 MP that had the maximum memory of 8 Meg on each side for a total of 16 Meg in MP mode. ?Kingston notified MVS development that they had some available machine time on the machine since it had successfully executed all the initial diagnostics. ?Some of the MVS development guys took their disk packs and drove over the river up to Kingston and loaded the disk drives and hit the load button. The lights blinked for several seconds - then went dead. ?Second attempt resulted in same thing. ?They then took a memory dump, and found nothing in memory. ?They took their disk packs and went back home. ?They discovered that the IPL bootstrap program would determine the memory size of the machine by going into a loop zeroing out 256 bytes of memory at a time expecting to get an addressing exception when it found the end of memory. ?Problem was that with 16 Meg the addressing exception never occurred. ?The 32 bit address went above 16 Meg, but only the low 24 bits were used so the loop clearing memory ended up zeroing out low core and wiped itself out coming from the other direction. ?Very amusing at the time.
Bertram Moshier All Messages By This Member #4990 Wonder how the VM guys handled this new system. toggle quoted message Show quoted text On Sun, Jan 15, 2023, 15:30 James Oswald via <oswaldjb=[email protected]> wrote: Regarding 24 bit addressing with 32 bit arithmetic.? When addressing memory in 24 bit mode, only the low 24 bits of the 32 bit generated address are used. I worked in Poughkeepsie in the early '70s adding MP support to MVS.? I can remember one incident when Kingston assembled the first fully configured 168 MP that had the maximum memory of 8 Meg on each side for a total of 16 Meg in MP mode.? Kingston notified MVS development that they had some available machine time on the machine since it had successfully executed all the initial diagnostics.? Some of the MVS development guys took their disk packs and drove over the river up to Kingston and loaded the disk drives and hit the load button. The lights blinked for several seconds - then went dead.? Second attempt resulted in same thing.? They then took a memory dump, and found nothing in memory.? They took their disk packs and went back home.? They discovered that the IPL bootstrap program would determine the memory size of the machine by going into a loop zeroing out 256 bytes of memory at a time expecting to get an addressing exception when it found the end of memory.? Problem was that with 16 Meg the addressing exception never occurred.? The 32 bit address went above 16 Meg, but only the low 24 bits were used so the loop clearing memory ended up zeroing out low core and wiped itself out coming from the other direction.? Very amusing at the time.
laddiehanus All Messages By This Member #4991 Probably the same way MVS 3.8J did - checked to see if the address was 16M and bailed out of the loop. Laddie toggle quoted message Show quoted text On Sunday, January 15, 2023, 3:46 PM, Bertram Moshier <herc370390vm@...> wrote: Wonder how the VM guys handled this new system. On Sun, Jan 15, 2023, 15:30 James Oswald via <oswaldjb=[email protected]> wrote: Regarding 24 bit addressing with 32 bit arithmetic.? When addressing memory in 24 bit mode, only the low 24 bits of the 32 bit generated address are used. I worked in Poughkeepsie in the early '70s adding MP support to MVS.? I can remember one incident when Kingston assembled the first fully configured 168 MP that had the maximum memory of 8 Meg on each side for a total of 16 Meg in MP mode.? Kingston notified MVS development that they had some available machine time on the machine since it had successfully executed all the initial diagnostics.? Some of the MVS development guys took their disk packs and drove over the river up to Kingston and loaded the disk drives and hit the load button. The lights blinked for several seconds - then went dead.? Second attempt resulted in same thing.? They then took a memory dump, and found nothing in memory.? They took their disk packs and went back home.? They discovered that the IPL bootstrap program would determine the memory size of the machine by going into a loop zeroing out 256 bytes of memory at a time expecting to get an addressing exception when it found the end of memory.? Problem was that with 16 Meg the addressing exception never occurred.? The 32 bit address went above 16 Meg, but only the low 24 bits were used so the loop clearing memory ended up zeroing out low core and wiped itself out coming from the other direction.? Very amusing at the time.
Fish Fish All Messages By This Member #4992 DOS/VS had an identical bug in it too as I recall. -- "Fish" (David B. Trout) Software Development Laboratories mail: fish@...

Previous Topic Next Topic