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comparison src/expr.c @ 15:1f598d89b9b0

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Started creating expression parser
author lost
date Thu, 23 Oct 2008 03:37:48 +0000
parents b28d7cb60779
children df0c4a46af8f
comparison
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14:b28d7cb60779 15:1f598d89b9b0
17 You should have received a copy of the GNU General Public License along with 17 You should have received a copy of the GNU General Public License along with
18 this program. If not, see <http://www.gnu.org/licenses/>. 18 this program. If not, see <http://www.gnu.org/licenses/>.
19 */ 19 */
20 20
21 /* 21 /*
22 This file contains implementations associated with the expression evaluator 22 This file contains the actual expression evaluator which uses the LWVAL
23 used by LWASM. 23 mechanism to store results.
24 */
25
26 #define __expr_c_seen__
27
28 #include <ctype.h>
29 #include <stdlib.h>
30
31 #include "expr.h"
32 #include "lwval.h"
33
34 // parse a single term out of the expression; return NULL if
35 // end of expression; return LWVAL_TYPE_ERR if error
36 /*
37 The following is handled by lwasm_parse_term:
38
39 - constants
40 - parsing a symbol
41 - unary -
42 - unary +
43 - ()
24 44
25 */ 45 */
46 LWVAL *lwasm_parse_term(char **ptr)
47 {
48 int sign = 1;
49 int s = 0;
50 LWVAL *rval;
51
52 start_term:
53 if (!**ptr || isspace(**ptr) || **ptr == ')')
54 return s ? lwval_construct_err(1) : NULL;
26 55
27 #include <malloc.h> 56 s = 1;
57 // unary + - NOOP
58 if (**ptr == '+')
59 {
60 (*ptr)++;
61 goto start_term;
62 }
63
64 // unary - - applied once the rest of the term is worked out
65 if (**ptr == '-')
66 {
67 (*ptr)++;
68 sign = -sign;
69 goto start_term;
70 }
71
72 // parens
73 if (**ptr == '(')
74 {
75 LWVAL *v;
76 (*ptr)++;
77 rval = lwasm_parse_expr(ptr);
78 if (**ptr != ')')
79 {
80 lwval_destroy(rval);
81 return lwval_construct_err(1);
82 }
83 (*ptr)++;
84 goto ret;
85 }
28 86
29 #define __expr_c_seen__ 87 // parse an actual term here; no more futzing with expressions
30 #include "expr.h"
31 88
32 LWVAL *lwval_construct_int(int value) 89 ret:
33 { 90 // apply negation if appropriate
34 LWVAL *v; 91 if (sign < 0)
35 92 lwval_neg(rval);
36 v = malloc(sizeof(LWVAL)); 93 return rval;
37 if (!v)
38 return NULL;
39
40 v -> lwval_type = LWVAL_TYPE_INT;
41 v -> dt.lwval_int = value;
42
43 return v;
44 } 94 }
45 95
46 void lwval_destroy(LWVAL *value) 96 // parse an expression
47 { 97 LWVAL *lwasm_parse_expr(char **ptr)
48 if (value)
49 free(value);
50 }
51
52 // v1 + v2 -> v3, return v3
53 LWVAL *lwval_add(LWVAL *v1, LWVAL *v2, LWVAL *v3)
54 { 98 {
55 } 99 }
56 100
57 // v1 - v2 -> v3, return v3 101 // attempt to evaluate/simplify expression
58 LWVAL *lwval_sub(LWVAL *v1, LWVAL *v2, LWVAL *v3) 102 int lwasm_eval_expr(LWVAL *expr)
59 { 103 {
60 } 104 }
61 105
62 // v1 * v2 -> v3, return v3
63 LWVAL *lwval_mul(LWVAL *v1, LWVAL *v2, LWVAL *v3)
64 {
65 }
66 106
67 // v1 / v2 -> v3, return v3
68 LWVAL *lwval_div(LWVAL *v1, LWVAL *v2, LWVAL *v3)
69 {
70 }
71
72 // v1 % v2 -> v3, return v3
73 LWVAL *lwval_mod(LWVAL *v1, LWVAL *v2, LWVAL *v3)
74 {
75 }