Introduction

MathEX is a mathematical expression evaluator written in C. It takes string as input and returns floating-point number as a result.

Features

• Supports arithmetic, bitwise and logical operators
• Supports variables
• Can be extended with custom functions
• Simple evaluation takes ~50 nanoseconds on an average PC
• Low memory usage makes it suitable for embedded systems
• Pure C99 with no external dependencies
• Good test coverage
• Easy to understand

Example

#include "expression.h"

/* Custom function that returns the sum of its two arguments */
static float add(struct expr_func *f, vec_expr_t args, void *c) {
    float a = expr_eval(&vec_nth(&args, 0));
    float b = expr_eval(&vec_nth(&args, 1));
    return a + b;
}

static struct expr_func user_funcs[] = {
    {"add", add, 0}, {NULL, NULL, 0},
};

int main() {
    const char *s = "x = 40, add(2, x)";
    struct expr_var_list vars = {0};
    struct expr *e = expr_create(s, strlen(s), &vars, user_funcs);
    if (!e) { printf("Syntax error"); return 1; }

    printf("result: %f\n", expr_eval(e));

    expr_destroy(e, &vars);
    return 0;
}

Output: result: 42.000000

API

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.

float 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)

Only the following functions from libc are used to reduce the footprint and make it easier to use:

• calloc, realloc and free - memory management
• isnan, isinf, fmodf, powf - math operations
• strlen, strncmp, strncpy, strtof - tokenizing and parsing

Running tests

To run all the tests and benchmarks, do make check.

License

Code is distributed under MIT X License that can be found in the LICENSE file.