I was invited to give a talk at the Silicon Valley Fig Forth Meeting on 2007 September 22. I like talking with this group. I know of no other group that have more in depth knowledge of of their computers. (Forth almost requires and appeals to that sort of user.)
When programming in Assembly Language I am in control of what my computer is doing, at least for a while; I find that satisfying. But the current vogue among computer users is to get as far from the real hardware as possible. Years ago this made sense when there were many different computer architectures and Universities, teachers and software vendors wanted something that could be used on a variety of computers. Educational efforts were to have "Standard Languages" and avoid machine dependent programming. Assembly is the epitome of using the features of a given machine.
Today the world is different. It looks like the Intel 8086 architecture and its descendents will be with us for ever. Even Apple has dropped the Motorola and Power PC chips and gone to the Intel line. So I ask: Why not take advantage of every idiosyncrasy of that instruction set?
The underlying theme of my talk was to show that compilers can never generate even good code, simply because there is no way to communicate to the compiler all the programmer knows about the problem and the nature of the data it designed to work on.
I chose to talk about generating a table of Prime Numbers using every trick I know of to make it as fast as possible.
qtest: scasd ;Test word in EAX against memory table jb qtestYes, it is only two instructions! The Intel Scan String Double word instruction is only one byte long, with a two byte jump back to it. This loop, scanning a growing table of composite numbers is where the vast majority of the time is spent when the program is running.
I know of no compiler that generates the Intel string instructions. Not even Forth!
Some details about a run where I generated 163,840,000 primes (the last one was: 3,424,462,051) numbers are here. I have a link to the notes I used for the talk, and a link to a .ZIP file where the programs I talked about can be down-loaded. However, initially at least, the use of the programs may be best understood by those who heard the talk.
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