eval_expr.c

#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>

typedef enum e_priority {
  PRIMARY = 0,
  UNARY,
  MULTIPLICATIVE,
  ADDITIVE,
  SHIFT,
  RELATIONAL,
  EQUALITY,
  AND,
  XOR,
  OR,
  LAND,
  LOR,
  CONDITIONAL,
  ASSIGN,
  EXPR,
  MAX = EXPR
} t_priority;

int stack[4096] = {0};
int idx = 0;
int ustack[4096] = {0};

#define ISWS(c) ((c) == ' ' || ((c) >= '\t' && (c) <= '\r'))
#define OPEND(c) (isdigit(c) || ISWS(c) || (c) == '$')

int *eval(char **s, t_priority p) {
  int *a;

  if (p == PRIMARY) {
    while (ISWS(**s)) ++*s;
    if (**s == '(')
      return (a = eval((++*s, s), MAX)), ++*s, a;
    if (**s == '$') {
      int i = 0;
      ++*s;
      while (isdigit(**s)) i = i * 10 + *(*s)++ - '0';
      return ustack + i;
    }
    a = stack + idx++;
    *a = 0;
    while (isdigit(**s)) *a = *a * 10 + *(*s)++ - '0';
    return a;
  }
  if (p == UNARY) {
    a = stack + idx;
    while (ISWS(**s)) ++*s;
    if (**s == '-' && OPEND(*(*s + 1)))
      return (*a = -*eval((++*s, s), p - 1)), a;
    if (**s == '+' && OPEND(*(*s + 1)))
      return eval((++*s, s), p - 1);
    if (**s == '~' && OPEND(*(*s + 1)))
      return (*a = ~*eval((++*s, s), p - 1)), a;
    if (**s == '!' && OPEND(*(*s + 1)))
      return (*a = !*eval((++*s, s), p - 1)), a;
    if (**s == '+' && *(*s + 1) == '+' && OPEND(*(*s + 2)))
      return (*a = ++*eval((*s += 2, s), p - 1)), a;
    if (**s == '-' && *(*s + 1) == '-' && OPEND(*(*s + 2)))
      return (*a = --*eval((*s += 2, s), p - 1)), a;
    return eval(s, p - 1);
  }
  a = eval(s, p - 1);
  int *i = stack + idx;
  while (1) {
    if (ISWS(**s))
      ++*s;
    else if (**s == '\0')
      return a;
    else if (p == MULTIPLICATIVE) {
      if (**s == '*' && OPEND(*(*s + 1)))
        a = ((*i = *a * *eval((++*s, s), p - 1)), i);
      else if (**s == '/' && OPEND(*(*s + 1)))
        a = ((*i = *a / *eval((++*s, s), p - 1)), i);
      else if (**s == '%' && OPEND(*(*s + 1)))
        a = ((*i = *a % *eval((++*s, s), p - 1)), i);
      else
        return a;
    } else if (p == ADDITIVE) {
      if (**s == '-' && OPEND(*(*s + 1)))
        a = ((*i = *a - *eval((++*s, s), p - 1)), i);
      else if (**s == '+' && OPEND(*(*s + 1)))
        a = ((*i = *a + *eval((++*s, s), p - 1)), i);
      else
        return a;
    } else if (p == SHIFT) {
      if (**s == '<' && *(*s + 1) == '<' && OPEND(*(*s + 2)))
        a = ((*i = *a << *eval((*s += 2, s), p - 1)), i);
      else if (**s == '>' && *(*s + 1) == '>' && OPEND(*(*s + 2)))
        a = ((*i = *a >> *eval((*s += 2, s), p - 1)), i);
      else
        return a;
    } else if (p == RELATIONAL) {
      if (**s == '<' && OPEND(*(*s + 1)))
        a = ((*i = *a < *eval((++*s, s), p - 1)), i);
      else if (**s == '>' && OPEND(*(*s + 1)))
        a = ((*i = *a > *eval((++*s, s), p - 1)), i);
      else if (**s == '<' && *(*s + 1) == '=' && OPEND(*(*s + 2)))
        a = ((*i = *a <= *eval((*s += 2, s), p - 1)), i);
      else if (**s == '>' && *(*s + 1) == '=' && OPEND(*(*s + 2)))
        a = ((*i = *a >= *eval((*s += 2, s), p - 1)), i);
      else
        return a;
    } else if (p == EQUALITY) {
      if (**s == '=' && *(*s + 1) == '=' && OPEND(*(*s + 2)))
        a = ((*i = *a == *eval((*s += 2, s), p - 1)), i);
      else if (**s == '!' && *(*s + 1) == '=' && OPEND(*(*s + 2)))
        a = ((*i = *a != *eval((*s += 2, s), p - 1)), i);
      else
        return a;
    } else if (p == AND) {
      if (**s == '&' && OPEND(*(*s + 1)))
        a = ((*i = *a & *eval((++*s, s), p - 1)), i);
      else
        return a;
    } else if (p == XOR) {
      if (**s == '^' && OPEND(*(*s + 1)))
        a = ((*i = *a ^ *eval((++*s, s), p - 1)), i);
      else
        return a;
    } else if (p == OR) {
      if (**s == '|' && OPEND(*(*s + 1)))
        a = ((*i = *a | *eval((++*s, s), p - 1)), i);
      else
        return a;
    } else if (p == LAND) {
      if (**s == '&' && *(*s + 1) == '&' && OPEND(*(*s + 2)))
        a = ((*i = *a && *eval((*s += 2, s), p - 1)), i);
      else
        return a;
    } else if (p == LOR) {
      if (**s == '|' && *(*s + 1) == '|' && OPEND(*(*s + 2)))
        a = ((*i = *a  || *eval((*s += 2, s), p - 1)), i);
      else
        return a;
    } else if (p == CONDITIONAL) {
      if (**s == '?' && *(*s + 1) == ':' && OPEND(*(*s + 2))) {
        int *b = eval((*s += 2, s), MAX);
        a = ((*i = *a  ? *a : *b), i);
      } else if (**s == '?' && OPEND(*(*s + 1))) {
        int *b = eval((++*s, s), MAX);
        while (ISWS(**s)) ++*s;
        int *c = eval((++*s, s), MAX);
        a = ((*i = *a ? *b : *c), i);
      } else
        return a;
    } else if (p == ASSIGN) {
      if (**s == '=' && OPEND(*(*s + 1)))
        *a = *eval((++*s, s), p - 1);
      else
        return a;
    } else if (p == EXPR) {
      if (**s == ',' && OPEND(*(*s + 1)))
        a = eval((++*s, s), p - 1);
      else
        return a;
    }
  }
}

int eval_expr(char *str) {
  return *(eval(&str, MAX));
}

int main(int ac, char **av) {
  printf("%d\n", eval_expr("($1 = ($2 = 3) + 42 * (1 - 2 / ($2 + 4) - 1 % 21) + $2) ? $1 + (1 >= 1 ? (1, 30 + 6) : 0) : 1"));
  return EXIT_SUCCESS;
}