OS/2 Professional/OS2PRO194.ISO/os2/prgramer/minix/expr.c

C/C++ Source or Header | 1989-12-27 | 5.4 KB | 256 lines

/* expr(1)  --  author Erik Baalbergen */
/* $Header: d:/rcs/D:/RCS/RCS/expr.c 1.2 89/12/27 02:49:00 RCA Exp $
 * $Log:    expr.c $
 * Revision 1.2  89/12/27  02:49:00  RCA
 * "&" and "|" operators don't work.
 *
 * Revision 1.1  89/12/27  02:41:48  RCA
 * Initial revision
 *
 */
/*
 * expr accepts the following grammar: expr ::= primary | primary
 * operator expr ; primary ::= '(' expr ')' | signed-integer ;
 * where the priority of the operators is taken care of. The
 * resulting value is printed on stdout. Note that the
 * ":"-operator is not implemented.
 */

#define EOI    0
#define OR    1
#define AND    2
#define LT    3
#define LE    4
#define EQ    5
#define NE    6
#define GE    7
#define GT    8
#define PLUS    9
#define MINUS    10
#define TIMES    11
#define DIV    12
#define MOD    13
#define COLON    14
#define LPAREN    15
#define RPAREN    16
#define OPERAND    20

#define MAXPRIO    6

struct op
{
   char   *op_text;
   short   op_num, op_prio;
}       ops[] =
{
   {
              "|", OR, 6
   }      ,
   {
              "&", AND, 5
   }      ,
   {
              "<", LT, 4
   }      ,
   {
              "<=", LE, 4
   }      ,
   {
              "=", EQ, 4
   }      ,
   {
              "!=", NE, 4
   }      ,
   {
              ">=", GE, 4
   }      ,
   {
              ">", GT, 4
   }      ,
   {
              "+", PLUS, 3
   }      ,
   {
              "-", MINUS, 3
   }      ,
   {
              "*", TIMES, 2
   }      ,
   {
              "/", DIV, 2
   }      ,
   {
              "%", MOD, 2
   }      ,
/* {":",    COLON,    1}, */
   {
              "(", LPAREN, -1
   }      ,
   {
              ")", RPAREN, -1
   }      ,
   {
              0, 0, 0
   }
};

long
eval(), expr();
char   *prog;
char  **ip;
struct op *ip_op;
main(argc, argv)
   char   *argv[];
{
long    res;
    if (argc == 1)
      {
      printf ("\n █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█");
      printf ("\n █ EXPR     (Do simple math)               $Author: RCA $   █");
      printf ("\n █          $Date: 89/12/27 02:49:00 $     $Revision: 1.2 $ █");
      printf ("\n █ Usage:   EXPR num1 operator num2 ...                     █");
      printf ("\n █          All arguments must be seperated by spaces.      █");
      printf ("\n █ Examples: EXPR 2 + 2 - 1                                 █");
      printf ("\n █           EXPR 4 * 9                                     █");
      printf ("\n █           EXPR 4 * ( 9 + 9 )                             █");
      printf ("\n █           EXPR 100 % 11 [modulo]                         █");
      printf ("\n █           EXPR 7 > 9                                     █");
      printf ("\n █           EXPR 7 < 9                                     █");
      printf ("\n █           EXPR 7 = 9                                     █");
      printf ("\n █           EXPR 7 >= 9                                    █");
      printf ("\n █           EXPR 7 != 9                                    █");
      printf ("\n █ Purpose: Do simple math from command line, without       █");
      printf ("\n █          invoking a special environment.                 █");
      printf ("\n █ OS:      Works under OS/2 or DOS.                        █");
      printf ("\n █ Credits: Eric Baalbergen                                 █");
      printf ("\n █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█\n");
      exit(1);
      }

   prog = argv[0];
   ip = &argv[1];
   res = expr(lex(*ip), MAXPRIO);
   if (*++ip != 0)
      syntax();
   printf("%d\n", res);
   exit(0);
}
lex(s)
   register char *s;
{
register struct op *op = ops;
   if (s == 0)
   {
      ip_op = 0;
      return EOI;
   }
   while (op->op_text)
   {
      if (strcmp(s, op->op_text) == 0)
      {
     ip_op = op;
     return op->op_num;
      }
      op++;
   }
   ip_op = 0;
   return OPERAND;
}

long
num(s)
   register char *s;
{
long l = 0;
long    sign = 1;
   if (*s == '\0')
      syntax();
   if (*s == '-')
   {
      sign = -1;
      s++;
   }
   while (*s >= '0' && *s <= '9')
l = l *10 + *s++ - '0';
   if (*s != '\0')
      syntax();
return sign * l;
}
syntax()
{
   write(2, prog, strlen(prog));
   write(2, ": syntax error\n", 15);
   exit(1);
}

long
expr(n, prio)
{
long    res;
   if (n == EOI)
      syntax();
   if (n == LPAREN)
   {
      if (prio == 0)
      {
     res = expr(lex(*++ip), MAXPRIO);
     if (lex(*++ip) != RPAREN)
        syntax();
      } else
     res = expr(n, prio - 1);
   } else
   if (n == OPERAND)
   {
      if (prio == 0)
     return num(*ip);
      res = expr(n, prio - 1);
   } else
      syntax();
   while ((n = lex(*++ip)) && ip_op && ip_op->op_prio == prio)
      res = eval(res, n, expr(lex(*++ip), prio - 1));
   ip--;
   return res;
}

long
eval(l1, op, l2)
   long    l1, l2;
{
   switch (op)
   {
   case OR:
      return l1 ? l1 : l2;
   case AND:
      return (l1 && l2) ? l1 : 0;
   case LT:
      return l1 < l2;
   case LE:
      return l1 <= l2;
   case EQ:
      return l1 == l2;
   case NE:
      return l1 != l2;
   case GE:
      return l1 >= l2;
   case GT:
      return l1 > l2;
   case PLUS:
      return l1 + l2;
   case MINUS:
      return l1 - l2;
   case TIMES:
      return l1 * l2;
   case DIV:
      return l1 / l2;
   case MOD:
      return l1 % l2;
   }
   fatal();
}
fatal()
{
   write(2, "fatal\n", 6);
   exit(1);
}