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Postings from July 2002
I've been trying to make sense of the current status of keyed access at all levels, from the assembler through the ops to the vtables and it has to be said that the harder I look the more confused I seem to become... It all seems to be a bit of a mess at the moment, and I'd like to have a go at cleaning it up but first of all I need to work out how it is all supposed to work. It is clear that the encoding currently used by the assembler does not match that specified by PDD 8 as the following examples show: Instruction PDD 8 Encoding Actual Current Encoding set P1["hi"], 1234 set_p_kc_ic set_keyed_p_sc_ic set P1[S1], 1234 set_p_r_ic set_keyed_p_s_ic set P1[1], 1234 set_p_kc_ic set_keyed_integer_p_ic_ic set P1[I1], 1234 set_p_r_ic set_keyed_integer_p_k_ic set P1[S1], P2[S2] set_p_r_p_r set_keyed_p_s_p_s set P1[I1], P2[S2] set_p_kc_p_r set_keyed_keyed_integer_p_i_p_s Obviously this is a complete nonsense. To be honest I suspect that both encodings have problems, The PDD 8 encoding uses kc and r (why not kc and k?) to encode the keys regardless of their type so the op has no way of knowing what sort of argument it is dealing with. The currently implemented system distinguishes the operand types OK but trys to differentiate between ops with an integer key and those with other types of keys which all falls apart when you have a combination of integer and non-integer keys in the same instruction. Once we get to multi-component keys things just get even worse. If we believe PDD 8 then the syntax should be: set P1[I1;I2], I3 But what is currently implemented is this: set P1[k;I1;I2], I3 In addition it appears that the current implementation would turn that instrucion into this encoding: set_keyed_integer_p_k_k_i Where each component of the key becomes a separate argument, thereby requiring an infinite number of ops to cope with an infinite number of possible key components. There is a suggestion in PDD 8 that this should be encoded as this: set_p_kc_i With the key constant actually referring to an entry in the constant table that encodes the key. Moving on the from the assembler I'm not sure how the recent addition of the _keyed_int vtable methods interacts with all this - they appear to be at odds with PDD 8 anyway which appears to want to avoid the kind of vtable explosion that they promote. Anyhow, that's probably enough for now... If anybody can elighten me about how all this is supposed to work then I'll try and knock it all into shape, starting with making sure that PDD 8 is accurate. Tom -- Tom Hughes (tom@compton.nu) http://www.compton.nu/Thread Next