kcalc is a mathematical expression evaluator and takes string as input, returning fixed-point numbers.
- Arithmetic, bitwise and logical operators;
- Flexible variables;
- Customized functions;
kcalc introduces a fixed-point number representation for fractional values: one 32-bit size is divided into mantissa (28 bits), sign (1 bit) and exponent (3 bits).
MSB 31 4 3 2 1 0 LSB
+----------------------------------+------+----------+
| mantissa | sign | exponent |
+----------------------------------+------+----------+
Build and install the module
$ make
$ sudo insmod calc.ko
$ sudo chmod 0666 /dev/calcThen simply send the expression to the module
$ echo -ne "3*5\0" > /dev/calcThe expected output in dmesg should be:
calc: Received 3 -> 3*5
Result: 240The result seems incorrect because we did not transform the value to normal representation. You can use the utlity to convert values into human readable form:
$ source scripts/eval.sh
$ fromfixed 240Then, you can get 15, which is the exact result for expression 3*5.
You can check file scripts/test.sh for more examples about the expressions. Alteratively,
execue make check for the same script.
$ scripts/test.sh
... Information generated by modinfo ...
Testing 6*7 ...
42
Testing 1980+1 ...
1981
Testing 2019-1 ...
2018
Testing 42/6 ...
7
Testing 1/3 ...
.33333330000000000000
Testing 1/3*6+2/4 ...
2.49999980000000000000
Testing (1/3)+(2/3) ...
.99999990000000000000
Testing (2145%31)+23 ...
29struct expr *expr_create(const char *s, size_t len, struct expr_var_list *vars, struct expr_func *funcs) - returns compiled expression from the given
string. If expression uses variables - they are bound to vars, so you can
modify values before evaluation or check the results after the evaluation.
int expr_eval(struct expr *e) - evaluates compiled expression.
void expr_destroy(struct expr *e, struct expr_var_list *vars) - cleans up
memory. Parameters can be NULL (e.g. if you want to clean up expression, but
reuse variables for another expression).
struct expr_var *expr_var(struct expr_var *vars, const char *s, size_t len) -
returns/creates variable of the given name in the given list. This can be used
to get variable references to get/set them manually.
- Arithmetics:
+,-,*,/,%(remainder),**(power) - Bitwise:
<<,>>,&,|,^(xor or unary bitwise negation) - Logical:
<,>,==,!=,<=,>=,&&,||,!(unary not) - Other:
=(assignment, e.g.x=y=5),,(separates expressions or function parameters)
kcalcis released under the MIT License. Use of this source code is governed by
a MIT License that can be found in the LICENSE file.