calc_005.re

a little DFA compiler.

/* re2c lesson 001_upn_calculator, calc_005, (c) M. Boerger 2006 - 2007 */
/*!ignore:re2c

- turning this lesson into an easy calculator
  . We are going to write an UPN calculator so we need an additional rule to
    ignore white space.
  . Then we need to store the scanned input somewhere and do our math on it.
  . Also we need to scan all arguments since the main c code gets the input
    split up into chunks.
  . In contrast to what we did before we now add a variable res that holds the 
    scanner state. We initialize that variable to 0 and quit the loop when it
    is non zero. This will also be our return value so that we can use it in
    function main to generate error information.
  . To support operating systems where ' and " get passed in program arguments
    we check for them being first and last input character. If so we correct
    input pointer and input length. Since now our scanner might not see a 
    terminating zero we change YYLIMIT again and drop the special zero rule.
*/

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

#define DEBUG(stmt) stmt

int  stack[4];
int  depth = 0;

int push_num(const char *t, const char *l, int radix)
{
	int num = 0;
	
	if (depth >= sizeof(stack))
	{
		return 3;
	}

	--t;
	while(++t < l)
	{
		num = num * radix + (*t - '0');
	}
	DEBUG(printf("Num: %d\n", num));

	stack[depth++] = num;
	return 0;
}

int stack_add()
{
	if (depth < 2) return 4;
	
	--depth;
	stack[depth-1] = stack[depth-1] + stack[depth];
	return 0;
}

int stack_sub()
{
	if (depth < 2) return 4;

	--depth;
	stack[depth-1] = stack[depth-1] - stack[depth];
	return 0;
}

int scan(char *s, int l)
{
	char *p = s;
	char *q = 0;
	char *t;
	int res = 0;

#define YYCTYPE         char
#define YYCURSOR        p
#define YYLIMIT         (s+l+1)
#define YYMARKER        q
#define YYFILL(n)		{ return depth == 1 ? 0 : 2; }
	
	while(!res)
	{
		t = p;
/*!re2c
	re2c:indent:top = 2;

	DIGIT	= [0-9] ;
	OCT		= "0" DIGIT+ ;
	INT		= "0" | ( [1-9] DIGIT* ) ;
	WS		= [ \t]+ ;

	WS		{ continue; }
	OCT		{ res = push_num(t, p, 8);	continue; }
	INT		{ res = push_num(t, p, 10); continue; }
	"+"		{ res = stack_add();		continue; }
	"-"		{ res = stack_sub();		continue; }
	[^]		{ res = 1; 					continue; }
*/
	}
	return res;
}

int main(int argc, char **argv)
{
	if (argc > 1)
	{
		char *inp;
		int res = 0, argp = 0, len;
		
		while(!res && ++argp < argc)
		{
			inp = argv[argp];
			len = strlen(inp);
			if (inp[0] == '\"' && inp[len-1] == '\"')
			{
				++inp;
				len -=2;
			}
			res = scan(inp, len);
		}
		switch(res)
		{
		case 0:
			printf("Result: %d\n", stack[0]);
			return 0;
		case 1:
			fprintf(stderr, "Illegal character in input.\n");
			return 1;
		case 2:
			fprintf(stderr, "Premature end of input.\n");
			return 2;
		case 3:
			fprintf(stderr, "Stack overflow.\n");
			return 3;
		case 4:
			fprintf(stderr, "Stack underflow.\n");
			return 4;
		}
	}
	else
	{
		fprintf(stderr, "%s <expr>\n", argv[0]);
		return 0;
	}
}