On Thursday 04 October 2001 12:05 pm, Dan Sugalski wrote: > At 11:29 AM 10/4/2001 -0400, Bryan C. Warnock wrote: > >Just the fact that we needed this patch in the first place indicates that > >we're not doing *nearly* enough talking beforehand of some of the > >particulars of Dan's overall design. > > That's the thing, though--we *don't* need this patch, not for integer > constants. It's actually detrimental to performance in many ways. > > Parrot guarantees you can embed 32-bit signed integer constants in the > instruction stream, and that's it. These constants are used to load up > integer registers, sure, but they're also used for jump offsets. Integer > *variable* constants should go in the constant table. We don't have any of > those yet, though. They come in with the PMC stuff.
Within t/, I count 42 instances of an integer constant being used as something other than a jump or branch offset. So let's just work this out, shall we? * A parrot bytecode entity. (Each distinct item of an optree - the opcodes and its arguments). Constant size throughout the bytecode. Is it a fixed size across all platforms? We've been saying 32 bits. What about platforms that don't have a native 32 bit entity (both larger and smaller - Crays and embedded) Is there a minimum size? Absolute or relative. (Absolute, like 16 bit, or relative, like size of the opcode) Is there a maximum size? Absolute or relative. Byte-order and bit-order. Native or standardized. * A parrot opcode. Most of the same questions as above. We'll talk about the actual opcode numbers separately. * Opcode interval constants (how far between opcodes, for jumping and branching) Fixed to size of a bytecode entity. Signed. A minimum size would affect the sizes above. What happens if a jump interval is larger than the type that contains it? * Integer constants Signed. Minimum size? (Size of bytecode or opcode, most likely. But again, what about platforms where that may not be a native type.) Maximum size? What do we do if an integer constant fits inside a bytecode entity? What do we do if an integer constant doesn't fit inside a bytecody entity, but fits inside an integer entity? What do we do if an integer constant doesn't fit inside an integer entity? * Numeric constants Signed. What do we do if a numerical constant fits inside a bytecode entity? (a 32 bit floating point type). What do we do if a numerical constant doesn't fit inside a bytecody entity, but fits inside a numerical entity? What do we do if a numerical constant doesn't fit inside a numerical entity? Native or standardized? * Constant table offsets Unsigned. What happens if (shudder) we have have an offset greater than the type that can represent it? *** Yes, some of them are right silly questions, but since computer programs are "default allow', we've got to address them. Limits are a good thing, and even better if we define what they are, (particularly because we're going to so much trouble to make Perl limitless.) -- Bryan C. Warnock [EMAIL PROTECTED]
