Comment by fjfaase
7 years ago
We live in a world were ever PC has at least 2 Gbyte of ram and most CPU's are 64 bits, the section 'Data Representation' begins to explain how 'everything' can be stored in a single 32-bit integer, if we limit integers to 30 bits. What the hack?
Generating 64-bit code would be simpler in many ways, but I decided not to go into it until the basic language features are put in place. The extent of the changes involved in switching to amd64 will help directly show why having an intermediate representation for the generated code would be valuable.
Besides, if you're looking for a high-performance Scheme that fully utilizes all available system resources, there are definitely better options available. :)
For your initial design you could also have chosen to use an additional byte to represent the type of the value. As representing the type would only require 2 or 3 bits, some bits will be unused (probably some more, due to alignment requirements), but maybe later on in the development of the compiler, those bits could be used to store some additional information. That would have made your code a lot simpler.
As you probably want to combine these valuse together into some structures representing the various language constructs, an additional byte to represent the type of the structure, and thus the type of its elements, would also be needed. Than you could do away with the extra bits representing the type.
I just think this is premature optimization and making things unneccessary complex especially for your readers who might want to learn something from it.
The types of user-defined "structures" are usually identified by a tag inside the structure, not encoded in the pointer as for the few primitive types.
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Keeping values small is still useful for the sake of CPU cache
Yes, RAM is aplenty, lets have every program use it to its fullest :-P
Also known as "unused RAM is wasted RAM".
https://cr.yp.to/bib/1995/wirth.pdf
Most CPUs are 8-bit with 32-bit beginning to take over. They usually don't have more than 256K.
Most CPUs aren't in self-hosting systems.
Yes they are. Embedded applications outnumber top end computers by an order of magnitude.
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It's premature optimisation... Java has conditioned everyone to believe that boxing variables is slow.
As Bill Gates was alleged to have said "640k ought to be enough for anybody."
He did not say that, sorry.
But he did say we wouldn't likely see speeds in excess of 64kbps. I save that article for decades, still have it somewhere in a filing cabinet, even though it's been scrubbed from the internet.
He was referencing the limitations of copper POTS, of course. But I still found it funny (if I recall correctly, it was printed side-by-side with his debunking of the 'you only need so much ram' quote).
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but he was alleged to !