On Nov 24, 2011, at 15:49, John Gilmore wrote: > What's past is prologue. There are historic reasons why, for example, > > |&termc setc '-201' > |&terma seta &termc > > sets &terma NOT to arithmetic -201 but to arithmetic +201. If you > want to preserve algebraic values you must use the D2A and A2D bifs or > RYO. This is counter-intuitive if you do not know the history, but > low-level changes in the behavior of the HLASM to make it more > 'reasonable' would break many, a great many, existing routines. > And yet I wonder about the history. Pure speculation, but it's marginally plausible that during design, there was some emulation and cross-development, before availability of real s/360 hardware on 709/7090/7094 systems. These all used sign-magnitude representation in their arithmetic registers, but twos-complement in index registers (well, actually unsigned modulo 2^15). A consequence was that in FORTRAN, if the programmer used a negative value as a subscript, no error was reported, but the magnitude would be loaded into an index register. It's possible that a cross- assembler on the 7094 could exhibit similar behavior converting from 36-bit native to 32-bit target representation, and that that could have become institutionalized so early to plague us to this day.
Have I seen this misbehavior elsewhere in HLASM? -- gil
