Jacob Repp

As a big fan of computer history and folklore I found this extremely interesting .

http://www.interact-sw.co.uk/altair/index2.html

“SyntaxCheck (RST 1)

Here is a truly beautiful piece of code, it’s Golden Weasel richly deserved. It’s used at run-time to check syntax in a very cool way : the byte immediately following an RST 1 instruction is not the following instruction, but the keyword or operator ID that’s expected to appear in the program at that point. If the keyword or operator is not present, then it Syntax Errors out, but if it is present then the return address is fixed-up - ie advanced one byte - and the function falls into NextChar so the caller has even less work to do. I honestly doubt syntax checks could be done more efficiently than this. Sheer bloody genius.”

The introduction to the usage of 8080 Restart functions is also particularly interesting.

Related posts:

• The history of the C language

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