RSS
Website| Tuesday, February 24, 2009 |
  Expression Evaluation in Z80 Assembly | ||
Posted - 2/24/2009 6:39:11 PM | ||
| The expression evaluators I've written in the past have been memory hungry and complex. Reading the BBC BASIC ROM user's guide introduced me to the concept of expression evaluation using top-down analysis, which only uses a small amount of constant RAM and the stack. I took some time out over the weekend to write an expression evaluator in Z80 assembly using this technique. It can take an expression in the form of a NUL-terminated string, like this: .db "(-8>>2)+ceil(pi())+200E-2**sqrt(abs((~(2&4)>>>(30^sin(rad(90))))-(10>?1)))",0 and produce a single answer (or an error!) in the form of a floating-point number. The source code and some notes can be downloaded here. I initially wrote a simple evaluator using 32-bit integers. I supported the operations the 8-bit Z80 could do relatively easily (addition, subtraction, shifts and logical operations) and got as far as 32-bit multiplication before deciding to use BBC BASIC's floating-point maths package instead. The downside is that BBC BASIC has to be installed (the program searches for the application and calls its FPP routine). I'm not sure if the technique used is obvious (I'd never thought of it) but it works well enough and the Z80 code should be easy to follow - someone may find it useful.  | ||
|
Comments
|
Journal of benryves | |
 | Extrarius GDNet+
Member since: 4/1/2002 From: Psionic Ward | |||
Posted - 2/24/2009 11:57:42 PM | ||||
Quote:Have you read Compilers: Principles, Techniques, and Tools? There is a new edition out that is probably far better, but I think you'd find even the old edition most helpful in writing compilers. It's one of the few books I've seen that covers the theory well - far too many skip theory almost entirely and end up being little more than code dumps between paragraphs of implementation details. | ||||
| ||||
 | benryves GDNet+
Member since: 9/4/2003 From: Purley, Greater London | |||
Posted - 2/25/2009 6:41:38 AM | ||||
| No, I've never read the book not studied compiler design or techniques so thanks for the recommendation - that sounds like a good book! | ||||
| ||||
| |
All times are ET (US) | |
| S | M | T | W | T | F | S |
1 | 2 | 3 | 4 | |||
5 | 6 | 7 | 8 | 9 | 10 | 11 |
12 | 13 | 14 | 15 | 16 | 17 | 18 |
19 | 20 | 21 | 22 | 23 | 24 | 25 |
26 | 27 | 28 | 29 | 30 |
OPTIONS
Track this Journal
ARCHIVES
August, 2010
July, 2010
June, 2010
April, 2010
March, 2010
February, 2010
January, 2010
December, 2009
November, 2009
October, 2009
August, 2009
June, 2009
May, 2009
March, 2009
February, 2009
January, 2009
December, 2008
November, 2008
October, 2008
September, 2008
August, 2008
July, 2008
June, 2008
May, 2008
April, 2008
March, 2008
February, 2008
November, 2007
October, 2007
September, 2007
August, 2007
July, 2007
May, 2007
April, 2007
February, 2007
January, 2007
December, 2006
November, 2006
October, 2006
September, 2006
August, 2006
July, 2006
June, 2006
May, 2006
April, 2006
March, 2006
February, 2006
January, 2006
December, 2005
November, 2005
October, 2005
September, 2005
August, 2005
April, 2005
February, 2005
January, 2005