All of the logical arithmetic instructions report overflow, but they differ from signed arithmetic in that
1. PoOps uses the term carry for an overflow on logical arithmetic instructions 2. The way the condition code is encoded is different 3. There is no overflow interrupt from a logical instuction I was thinking Z and should have written BO/BNO for S/370, which did not have branch relative. -- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 ________________________________________ From: IBM Mainframe Assembler List [[email protected]] on behalf of Paul Gilmartin [[email protected]] Sent: Thursday, April 21, 2022 12:04 PM To: [email protected] Subject: Re: Unexpected C code On Apr 21, 2022, at 08:43:55, Seymour J Metz wrote: > > The question is not whether it is possible to detect overflow, but rather how > easy it is. Instructions for signed arithmetic set the condition code > appropriately for signed operands, but not for unsigned operands, e.g., > adding 00000001 to FFFFFFFF with A gives a zero condition code while AL > gives an overflow condition code. If there were no AL instruction then > detecting the overflow would be more awkward. > I believe it's the opposite. A and S report overflow; AL and SL do not; rather, AL and SL report a carry from the MSB. On Apr 21, 2022, at 08:46:26, Seymour J Metz wrote: > > Well, in the case of S/370 the compiler could emit JO or JNO after the add. > That may be unnecessary. Simply enable trap on Overflow in the Program Mask. Depending on what recovery action the programmer intends to take. -- gil
