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/* SPDX-License-Identifier: GPL-2.0-or-later */
#ifndef EXPRESSION_H
#define EXPRESSION_H
#include <ctype.h>
#include <errno.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include "vec.h"
#define EXPRESSION_NAME_MAX 64
enum expression_error_code {
EXPRESSION_OK,
EXPRESSION_SYNTAX_ERROR,
EXPRESSION_PAREN_ERROR,
EXPRESSION_UNKNOWN_VARIABLE,
EXPRESSION_UNSET_VARIABLE,
EXPRESSION_DIVISION_BY_ZERO,
};
struct expression_error {
enum expression_error_code code;
size_t position;
};
struct expression_variable {
char name[EXPRESSION_NAME_MAX];
double value;
bool assigned;
};
struct expression_context {
struct vec variables;
};
static inline void expression_init(struct expression_context *ctx)
{
vec_init(&ctx->variables, struct expression_variable);
}
static inline void expression_destroy(struct expression_context *ctx)
{
vec_destroy(&ctx->variables);
}
static inline void expression_error(struct expression_error *error,
enum expression_error_code code,
size_t position)
{
if (error) {
error->code = code;
error->position = position;
}
}
static inline bool expression_name_start(unsigned char c)
{
return isalpha(c) || c == '_';
}
static inline bool expression_name_char(unsigned char c)
{
return isalnum(c) || c == '_';
}
static inline struct expression_variable *
expression_variable(struct expression_context *ctx, const char *name)
{
for (size_t i = 0; i < ctx->variables.size; ++i) {
struct expression_variable *v = vec_at(&ctx->variables, i);
if (strcmp(v->name, name) == 0) {
return v;
}
}
return NULL;
}
static inline bool expression_set_variable(struct expression_context *ctx,
const char *name,
double value)
{
if (!expression_name_start((unsigned char)name[0]) ||
strlen(name) >= EXPRESSION_NAME_MAX) return false;
for (const unsigned char *p = (const unsigned char *)name + 1; *p; ++p) {
if (!expression_name_char(*p)) {
return false;
}
}
struct expression_variable *v = expression_variable(ctx, name);
if (!v) {
struct expression_variable item = { .value = value, .assigned = true };
strcpy(item.name, name);
if (!vec_push_back(&ctx->variables, &item)) {
return false;
}
} else {
v->value = value;
v->assigned = true;
}
return true;
}
static inline bool expression_collect_variables(struct expression_context *ctx,
const char *text,
struct expression_error *error)
{
vec_clear(&ctx->variables);
for (size_t i = 0; text[i];) {
unsigned char c = (unsigned char)text[i];
if (isspace(c)) {
++i;
} else if (expression_name_start(c)) {
size_t start = i++;
while (expression_name_char((unsigned char)text[i])) {
++i;
}
size_t length = i - start;
if (length >= EXPRESSION_NAME_MAX) {
expression_error(error, EXPRESSION_SYNTAX_ERROR, start);
return false;
}
char name[EXPRESSION_NAME_MAX];
memcpy(name, text + start, length);
name[length] = '\0';
if (!expression_variable(ctx, name)) {
struct expression_variable item = { .assigned = false };
strcpy(item.name, name);
if (!vec_push_back(&ctx->variables, &item)) {
expression_error(error, EXPRESSION_SYNTAX_ERROR, start);
return false;
}
}
} else if (isdigit(c) || c == '.' || c == '+' || c == '-' ||
c == '*' || c == '/' || c == '(' || c == ')') {
++i;
} else {
expression_error(error, EXPRESSION_SYNTAX_ERROR, i);
return false;
}
}
expression_error(error, EXPRESSION_OK, 0);
return true;
}
struct expression_parser {
const char *text;
size_t position;
const struct expression_context *ctx;
struct expression_error *error;
};
static inline void expression_skip(struct expression_parser *p)
{
while (isspace((unsigned char)p->text[p->position])) {
++p->position;
}
}
static inline bool expression_parse_sum(struct expression_parser *, double *);
static inline bool expression_parse_primary(struct expression_parser *p,
double *out)
{
expression_skip(p);
size_t start = p->position;
char c = p->text[start];
if (c == '(') {
++p->position;
if (!expression_parse_sum(p, out)) return false;
expression_skip(p);
if (p->text[p->position] != ')') {
expression_error(p->error, EXPRESSION_PAREN_ERROR, p->position);
return false;
}
++p->position;
return true;
}
if (isdigit((unsigned char)c) || c == '.') {
char *end;
errno = 0;
*out = strtod(p->text + start, &end);
if (end == p->text + start || errno == ERANGE) {
expression_error(p->error, EXPRESSION_SYNTAX_ERROR, start);
return false;
}
p->position = (size_t)(end - p->text);
return true;
}
if (expression_name_start((unsigned char)c)) {
char name[EXPRESSION_NAME_MAX];
size_t length;
++p->position;
while (expression_name_char((unsigned char)p->text[p->position])) ++p->position;
length = p->position - start;
if (length >= sizeof(name)) {
expression_error(p->error, EXPRESSION_SYNTAX_ERROR, start);
return false;
}
memcpy(name, p->text + start, length);
name[length] = '\0';
const struct expression_variable *v =
expression_variable((struct expression_context *)p->ctx, name);
if (!v) expression_error(p->error, EXPRESSION_UNKNOWN_VARIABLE, start);
else if (!v->assigned) expression_error(p->error, EXPRESSION_UNSET_VARIABLE, start);
else *out = v->value;
return v && v->assigned;
}
expression_error(p->error, EXPRESSION_SYNTAX_ERROR, start);
return false;
}
static inline bool expression_parse_unary(struct expression_parser *p, double *out)
{
expression_skip(p);
char c = p->text[p->position];
if (c == '+' || c == '-') {
++p->position;
if (!expression_parse_unary(p, out)) return false;
if (c == '-') *out = -*out;
return true;
}
return expression_parse_primary(p, out);
}
static inline bool expression_parse_product(struct expression_parser *p, double *out)
{
if (!expression_parse_unary(p, out)) return false;
for (;;) {
expression_skip(p);
char op = p->text[p->position];
if (op != '*' && op != '/') return true;
++p->position;
double rhs;
if (!expression_parse_unary(p, &rhs)) return false;
if (op == '/') {
if (rhs == 0.0) {
expression_error(p->error, EXPRESSION_DIVISION_BY_ZERO, p->position);
return false;
}
*out /= rhs;
} else *out *= rhs;
}
}
static inline bool expression_parse_sum(struct expression_parser *p, double *out)
{
if (!expression_parse_product(p, out)) return false;
for (;;) {
expression_skip(p);
char op = p->text[p->position];
if (op != '+' && op != '-') return true;
++p->position;
double rhs;
if (!expression_parse_product(p, &rhs)) return false;
if (op == '+') *out += rhs;
else *out -= rhs;
}
}
static inline bool expression_eval(const struct expression_context *ctx,
const char *text,
double *result,
struct expression_error *error)
{
struct expression_parser p = { text, 0, ctx, error };
if (!expression_parse_sum(&p, result)) return false;
expression_skip(&p);
if (p.text[p.position]) {
expression_error(error,
p.text[p.position] == ')' ? EXPRESSION_PAREN_ERROR
: EXPRESSION_SYNTAX_ERROR,
p.position);
return false;
}
expression_error(error, EXPRESSION_OK, 0);
return true;
}
#endif /* EXPRESSION_H */
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