On Mon, Jan 9, 2012 at 4:54 PM, Edward Jaffe <edja...@phoenixsoftware.com>wrote:
> On 1/9/2012 1:40 PM, Steve Comstock wrote: > >> Here's what I'm thinking: >> >> LMG R2,R4,datetimen - put datetime into R2/R3 >> (use 64 bits in each reg) >> and put datetimes into R4/R5 >> (use 64 bits in each reg) >> SLBGR R3,R5 >> SLBGR R2,R4 >> > > You're not supposed to use a logical subtract 'with borrow' on the > low-order > part. You use it only on the high-order part--AFTER doing a logical > subtract > 'without borrow' on the low-order part. > Ed is again correct. This technique can be used to write routines that perform fixed-point arithmetic with arbitrarily long numbers, since you can perform the subtraction four bytes (or eight bytes) at a time, propagating a borrow should one occur. -- Mike Shaw MVS/QuickRef Support Group Chicago-Soft, Ltd.
