https://github.com/sysprog21/kcalc-fixed
Math expression evaluation as Linux kernel module, fixed-point implementation
https://github.com/sysprog21/kcalc-fixed
Last synced: 29 days ago
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Math expression evaluation as Linux kernel module, fixed-point implementation
- Host: GitHub
- URL: https://github.com/sysprog21/kcalc-fixed
- Owner: sysprog21
- License: mit
- Created: 2020-10-19T22:56:08.000Z (over 4 years ago)
- Default Branch: master
- Last Pushed: 2020-10-29T13:39:08.000Z (over 4 years ago)
- Last Synced: 2025-05-08T23:54:20.979Z (29 days ago)
- Language: C
- Size: 64.5 KB
- Stars: 4
- Watchers: 2
- Forks: 14
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# kcalc: in-kernel math expression evaluation for Linux
kcalc is a mathematical expression evaluator and takes string as
input, returning fixed-point numbers.
## Features
* Arithmetic, bitwise and logical operators;
* Flexiable variables;
* Customized functions;
## Fixed-point representation
kcalc introduces a fixed-point number representation for fractional values.
## Usage:
Build and install the module
```shell
$ make
$ sudo insmod calc.ko
$ sudo chmod 0666 /dev/calc
```
Then simply send the expression to the module
```shell
$ echo -ne "3*5\0" > /dev/calc
```
The expected output in `dmesg` should be:
```shell
calc: Received 3 -> 3*5
Result: 64424509440
```
The result seems incorrect since we do not transform the value to normal representation.
You can use the utlity to convert values into human readable form:
```shell
$ ./eval 64424509440
```
Then, you can get `15.000000`, which is the exact result of expression `3*5`.
You can check file `scripts/test.sh` for more examples about the expressions. Alteratively,
execue `make check` for the same script.
```shell
$ 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 ...
29
```
## Internals
`struct 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.
## Supported operators
* Arithmetics: `+`, `-`, `*`, `/`, `%` (remainder), `**` (power)
* Bitwise: `<<`, `>>`, `&`, `|`, `^` (xor or unary bitwise negation)
* Logical: `<`, `>`, `==`, `!=`, `<=`, `>=`, `&&`, `||`, `!` (unary not)
* Other: `=` (assignment, e.g. `x=y=5`), `,` (separates expressions or function parameters)
## License
`kcalc`is released under the MIT License. Use of this source code is governed by
a MIT License that can be found in the LICENSE file.