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298
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1 /*
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2 expr.c
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300
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3 Copyright © 2009 William Astle
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298
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4
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5 This file is part of LWLINK.
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6
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7 LWLINK 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
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23 */
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24
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25 #define __expr_c_seen__
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26
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27 #include <ctype.h>
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28 #include <stdlib.h>
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29 #include <string.h>
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30
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31 #include "expr.h"
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32 #include "util.h"
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33
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34 lw_expr_stack_t *lw_expr_stack_create(void)
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35 {
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36 lw_expr_stack_t *s;
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37
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38 s = lw_malloc(sizeof(lw_expr_stack_t));
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39 s -> head = NULL;
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40 s -> tail = NULL;
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41 return s;
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42 }
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43
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44 void lw_expr_stack_free(lw_expr_stack_t *s)
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45 {
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46 while (s -> head)
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47 {
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48 s -> tail = s -> head;
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49 s -> head = s -> head -> next;
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50 lw_expr_term_free(s -> tail -> term);
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51 lw_free(s -> tail);
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52 }
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53 lw_free(s);
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54 }
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55
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56 void lw_expr_term_free(lw_expr_term_t *t)
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57 {
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58 if (t)
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59 {
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60 if (t -> term_type == LW_TERM_SYM)
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61 lw_free(t -> symbol);
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62 lw_free(t);
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63 }
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64 }
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65
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66 lw_expr_term_t *lw_expr_term_create_oper(int oper)
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67 {
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68 lw_expr_term_t *t;
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69
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70 t = lw_malloc(sizeof(lw_expr_term_t));
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71 t -> term_type = LW_TERM_OPER;
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72 t -> value = oper;
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73 return t;
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74 }
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75
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76 lw_expr_term_t *lw_expr_term_create_int(int val)
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77 {
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78 lw_expr_term_t *t;
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79
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80 t = lw_malloc(sizeof(lw_expr_term_t));
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81 t -> term_type = LW_TERM_INT;
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82 t -> value = val;
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83 return t;
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84 }
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85
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86 lw_expr_term_t *lw_expr_term_create_sym(char *sym, int symtype)
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87 {
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88 lw_expr_term_t *t;
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89
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90 t = lw_malloc(sizeof(lw_expr_term_t));
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91 t -> term_type = LW_TERM_SYM;
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92 t -> symbol = lw_strdup(sym);
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93 t -> value = symtype;
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94 return t;
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95 }
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96
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97 lw_expr_term_t *lw_expr_term_dup(lw_expr_term_t *t)
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98 {
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99 switch (t -> term_type)
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100 {
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101 case LW_TERM_INT:
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102 return lw_expr_term_create_int(t -> value);
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103
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104 case LW_TERM_OPER:
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105 return lw_expr_term_create_oper(t -> value);
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106
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107 case LW_TERM_SYM:
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108 return lw_expr_term_create_sym(t -> symbol, t -> value);
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109
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110 default:
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111 exit(1);
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112 }
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113 // can't get here
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114 }
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115
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116 void lw_expr_stack_push(lw_expr_stack_t *s, lw_expr_term_t *t)
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117 {
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118 lw_expr_stack_node_t *n;
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119
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120 if (!s)
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121 {
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122 exit(1);
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123 }
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124
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125 n = lw_malloc(sizeof(lw_expr_stack_node_t));
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126 n -> next = NULL;
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127 n -> prev = s -> tail;
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128 n -> term = lw_expr_term_dup(t);
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129
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130 if (s -> head)
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131 {
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132 s -> tail -> next = n;
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133 s -> tail = n;
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134 }
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135 else
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136 {
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137 s -> head = n;
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138 s -> tail = n;
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139 }
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140 }
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141
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142 lw_expr_term_t *lw_expr_stack_pop(lw_expr_stack_t *s)
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143 {
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144 lw_expr_term_t *t;
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145 lw_expr_stack_node_t *n;
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146
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147 if (!(s -> tail))
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148 return NULL;
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149
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150 n = s -> tail;
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151 s -> tail = n -> prev;
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152 if (!(n -> prev))
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153 {
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154 s -> head = NULL;
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155 }
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156
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157 t = n -> term;
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158 n -> term = NULL;
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159
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160 lw_free(n);
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161
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162 return t;
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163 }
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164
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165 /*
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166 take an expression stack s and scan for operations that can be completed
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167
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168 return -1 on error, 0 on no error
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169
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170 possible errors are: division by zero or unknown operator
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171
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172 theory of operation:
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173
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174 scan the stack for an operator which has two constants preceding it (binary)
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175 or 1 constant preceding it (unary) and if found, perform the calculation
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176 and replace the operator and its operands with the result
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177
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178 repeat the scan until no futher simplications are found or if there are no
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179 further operators or only a single term remains
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180
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181 */
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182 int lw_expr_reval(lw_expr_stack_t *s, lw_expr_stack_t *(*sfunc)(char *sym, int stype, void *state), void *state)
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183 {
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184 lw_expr_stack_node_t *n, *n2;
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185 lw_expr_stack_t *ss;
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186 int c;
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187
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188 next_iter_sym:
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189 // resolve symbols
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190 // symbols that do not resolve to an expression are left alone
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191 for (c = 0, n = s -> head; n; n = n -> next)
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192 {
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193 if (n -> term -> term_type == LW_TERM_SYM)
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194 {
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195 ss = sfunc(n -> term -> symbol, n -> term -> value, state);
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196 if (ss)
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197 {
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198 c++;
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199 // splice in the result stack
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200 if (n -> prev)
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201 {
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202 n -> prev -> next = ss -> head;
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203 }
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204 else
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205 {
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206 s -> head = ss -> head;
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207 }
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208 ss -> head -> prev = n -> prev;
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209 ss -> tail -> next = n -> next;
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210 if (n -> next)
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211 {
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212 n -> next -> prev = ss -> tail;
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213 }
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214 else
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215 {
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216 s -> tail = ss -> tail;
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217 }
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218 lw_expr_term_free(n -> term);
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219 lw_free(n);
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220 n = ss -> tail;
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221
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222 ss -> head = NULL;
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223 ss -> tail = NULL;
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224 lw_expr_stack_free(ss);
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225 }
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226 }
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227 }
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228 if (c)
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229 goto next_iter_sym;
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230
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231 next_iter:
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232 // a single term
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233 if (s -> head == s -> tail)
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234 return 0;
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235
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236 // search for an operator
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237 for (n = s -> head; n; n = n -> next)
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238 {
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239 if (n -> term -> term_type == LW_TERM_OPER)
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240 {
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241 if (n -> term -> value == LW_OPER_NEG
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242 || n -> term -> value == LW_OPER_COM
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243 )
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244 {
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245 // unary operator
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246 if (n -> prev && n -> prev -> term -> term_type == LW_TERM_INT)
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247 {
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248 // a unary operator we can resolve
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249 // we do the op then remove the term "n" is pointing at
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250 if (n -> term -> value == LW_OPER_NEG)
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251 {
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252 n -> prev -> term -> value = -(n -> prev -> term -> value);
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253 }
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254 else if (n -> term -> value == LW_OPER_COM)
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255 {
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256 n -> prev -> term -> value = ~(n -> prev -> term -> value);
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257 }
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258 n -> prev -> next = n -> next;
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259 if (n -> next)
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260 n -> next -> prev = n -> prev;
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261 else
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262 s -> tail = n -> prev;
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263
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264 lw_expr_term_free(n -> term);
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265 lw_free(n);
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266 break;
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267 }
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268 }
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269 else
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270 {
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271 // binary operator
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272 if (n -> prev && n -> prev -> prev && n -> prev -> term -> term_type == LW_TERM_INT && n -> prev -> prev -> term -> term_type == LW_TERM_INT)
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273 {
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274 // a binary operator we can resolve
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275 switch (n -> term -> value)
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276 {
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277 case LW_OPER_PLUS:
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278 n -> prev -> prev -> term -> value += n -> prev -> term -> value;
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279 break;
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280
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281 case LW_OPER_MINUS:
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282 n -> prev -> prev -> term -> value -= n -> prev -> term -> value;
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283 break;
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284
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285 case LW_OPER_TIMES:
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286 n -> prev -> prev -> term -> value *= n -> prev -> term -> value;
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287 break;
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288
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289 case LW_OPER_DIVIDE:
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290 if (n -> prev -> term -> value == 0)
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291 return -1;
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292 n -> prev -> prev -> term -> value /= n -> prev -> term -> value;
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293 break;
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294
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295 case LW_OPER_MOD:
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296 if (n -> prev -> term -> value == 0)
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297 return -1;
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298 n -> prev -> prev -> term -> value %= n -> prev -> term -> value;
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299 break;
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300
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301 case LW_OPER_INTDIV:
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302 if (n -> prev -> term -> value == 0)
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303 return -1;
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304 n -> prev -> prev -> term -> value /= n -> prev -> term -> value;
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305 break;
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306
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307 case LW_OPER_BWAND:
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308 n -> prev -> prev -> term -> value &= n -> prev -> term -> value;
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309 break;
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310
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311 case LW_OPER_BWOR:
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312 n -> prev -> prev -> term -> value |= n -> prev -> term -> value;
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313 break;
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314
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315 case LW_OPER_BWXOR:
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316 n -> prev -> prev -> term -> value ^= n -> prev -> term -> value;
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317 break;
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318
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319 case LW_OPER_AND:
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320 n -> prev -> prev -> term -> value = (n -> prev -> term -> value && n -> prev -> prev -> term -> value) ? 1 : 0;
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321 break;
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322
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323 case LW_OPER_OR:
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324 n -> prev -> prev -> term -> value = (n -> prev -> term -> value || n -> prev -> prev -> term -> value) ? 1 : 0;
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325 break;
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326
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327 default:
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328 // return error if unknown operator!
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329 return -1;
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330 }
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331
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332 // now remove the two unneeded entries from the stack
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333 n -> prev -> prev -> next = n -> next;
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334 if (n -> next)
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335 n -> next -> prev = n -> prev -> prev;
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336 else
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337 s -> tail = n -> prev -> prev;
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338
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339 lw_expr_term_free(n -> term);
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340 lw_expr_term_free(n -> prev -> term);
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341 lw_free(n -> prev);
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342 lw_free(n);
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343 break;
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344 }
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345 }
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346 }
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347 }
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348 // note for the terminally confused about dynamic memory and pointers:
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349 // n will not be NULL even after the lw_free calls above so
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350 // this test will still work (n will be a dangling pointer)
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351 // (n will only be NULL if we didn't find any operators to simplify)
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352 if (n)
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353 goto next_iter;
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354
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355 return 0;
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356 }
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