On 25/06/2018 05:23, J. Gareth Moreton wrote:
Actually you're right - that is the fastest method (it's written O(1), by the way, if it doesn't depend on n). The drawback is that the large majority of instructions don't have such an optimisation procedure, so the table would be extremely sparse. There are 1,109 individual instructions on x86 that FPC currently supports. Come to think of it, even that is not too bad as far as memory goes - you're looking at 8,872 bytes on i386 (4 bytes for the instruction and 4 bytes for a pointer) and 17,744 bytes on x86-64 (8 bytes for each field), both are potentially cacheable on the CPU hence won't be too costly in regards to looking it up. Not sure why I overlooked that one. Thanks Martin.
While probably not worth it, but if you want to save memory (and only few entries have data): Use 2 maps:
map1: array[opcode] of byte; // I do not know how efficient reading bytes is....
maps the (hopefully fewer than 255 active entries) map2: array[byte] of codepointer
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