I developed this small ANSI C program at the university. It is a simple formula parser, useful for many situations, like an intelligent input in dialog boxes.
The gag in this parser is the possibility to compile formulas into p-code to get a major performance improvement while calculating. This is useful for formula plotters, etc., that uses the same formula only with different values.
In Parse.h some configurations can be done:
- ‘‘Dbl’’ is a typedef for the type of the calculation of the parser. Normally it should be ‘‘float’’ or ‘‘double’’. ‘‘TERM_COMPILER’’ activates the p-code compiler. If you use the formula only once, than you should disable it, otherwise enable it.
- buildTerm is called to compile an ASCII expression into p-code. If the ‘‘TERM_COMPILER’’ is not active, this routine does nothing.
- ‘‘calcTerm’’, ‘‘calcTerm1’’, ‘‘calcTerm2’’, ‘‘calcTerm3’’ calculates the current expression with no, 1, 2 or 3 parameters. The parameters are put into the variables ‘‘X’’, ‘‘Y’’ and ‘‘Z’’. Undefined variables have the value ‘‘HUGE_VAL’’.
Besides the trivial operations (‘’+‘’, ‘’-‘’, ‘’*‘’, ‘’/‘’, ‘’^‘’, with brackets) the parser also know the following functions:
| Name | Description |
|---|---|
| ‘‘PI’’ | the value PI (3.1415926…) |
| ‘‘E’’ | the value e (2.7182818) |
| ‘‘X’’, ‘‘Y’’, ‘‘Z’’ | the values X, Y, Z |
| ‘‘acos’’, ‘‘arccos’’ | the function cos–1(a) |
| ‘‘asin’’, ‘‘arcsin’’ | the function sin–1(a) |
| ‘‘atan’’, ‘‘arctan’’ | the function tan–1(a) |
| ‘‘atan2’’, ‘‘arctan2’’ | the function tan–1(a,b) |
| ‘‘ceil’’ | the function ceil(a) |
| ‘‘cos’’ | the function cos(a) |
| ‘‘cosh’’ | the function cosh(a) |
| ‘‘exp’’ | the function exp(a) |
| ‘‘floor’’ | the function floor(a) |
| ‘‘fmod’’ | the function fmod(a) |
| ‘‘log’’ | the function log(a) |
| ‘‘log10’’ | the function log10(a) |
| ‘‘pow’’ | the function pow(a,b) |
| ‘‘sin’’ | the function sin(a) |
| ‘‘sinh’’ | the function sinh(a) |
| ‘‘sqrt’’ | the function sqrt(a) |
| ‘‘tan’’ | the function tan(a) |
| ‘‘tanh’’ | the function tanh(a) |