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annotate 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
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1 /*
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2 expr.c
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3 Copyright © 2008 William Astle
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4
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5 This file is part of LWASM.
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6
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7 LWASM is free software: you can redistribute it and/or modify it under the
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8 terms of the GNU General Public License as published by the Free Software
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9 Foundation, either version 3 of the License, or (at your option) any later
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10 version.
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11
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12 This program is distributed in the hope that it will be useful, but WITHOUT
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13 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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14 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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15 more details.
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16
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17 You should have received a copy of the GNU General Public License along with
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18 this program. If not, see <http://www.gnu.org/licenses/>.
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19 */
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20
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21 /*
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22 This file contains the actual expression evaluator which uses the LWVAL
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23 mechanism to store results.
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24 */
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25
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26 #define __expr_c_seen__
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27
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28 #include <ctype.h>
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29 #include <stdlib.h>
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30
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31 #include "expr.h"
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32 #include "lwval.h"
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33
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34 // parse a single term out of the expression; return NULL if
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35 // end of expression; return LWVAL_TYPE_ERR if error
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36 /*
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37 The following is handled by lwasm_parse_term:
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38
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39 - constants
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40 - parsing a symbol
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41 - unary -
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42 - unary +
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43 - ()
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44
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45 */
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46 LWVAL *lwasm_parse_term(char **ptr)
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47 {
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48 int sign = 1;
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49 int s = 0;
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50 LWVAL *rval;
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51
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52 start_term:
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53 if (!**ptr || isspace(**ptr) || **ptr == ')')
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54 return s ? lwval_construct_err(1) : NULL;
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55
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56 s = 1;
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57 // unary + - NOOP
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58 if (**ptr == '+')
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59 {
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60 (*ptr)++;
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61 goto start_term;
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62 }
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63
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64 // unary - - applied once the rest of the term is worked out
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65 if (**ptr == '-')
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66 {
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67 (*ptr)++;
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68 sign = -sign;
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69 goto start_term;
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70 }
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71
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72 // parens
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73 if (**ptr == '(')
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74 {
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75 LWVAL *v;
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76 (*ptr)++;
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77 rval = lwasm_parse_expr(ptr);
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78 if (**ptr != ')')
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79 {
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80 lwval_destroy(rval);
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81 return lwval_construct_err(1);
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82 }
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83 (*ptr)++;
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84 goto ret;
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85 }
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86
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87 // parse an actual term here; no more futzing with expressions
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88
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89 ret:
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90 // apply negation if appropriate
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91 if (sign < 0)
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92 lwval_neg(rval);
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93 return rval;
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94 }
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95
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96 // parse an expression
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97 LWVAL *lwasm_parse_expr(char **ptr)
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98 {
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99 }
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100
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101 // attempt to evaluate/simplify expression
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102 int lwasm_eval_expr(LWVAL *expr)
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103 {
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104 }
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