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339
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1 /*
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2 expr.c
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3 Copyright © 2009 William Astle
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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 #include <config.h>
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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 #include <string.h>
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31
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32 #include "expr.h"
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33 #include "util.h"
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34
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35 lw_expr_stack_t *lw_expr_stack_create(void)
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36 {
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37 lw_expr_stack_t *s;
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38
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39 s = lw_malloc(sizeof(lw_expr_stack_t));
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40 s -> head = NULL;
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41 s -> tail = NULL;
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42 return s;
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43 }
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44
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45 void lw_expr_stack_free(lw_expr_stack_t *s)
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46 {
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47 while (s -> head)
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48 {
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49 s -> tail = s -> head;
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50 s -> head = s -> head -> next;
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51 lw_expr_term_free(s -> tail -> term);
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52 lw_free(s -> tail);
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53 }
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54 lw_free(s);
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55 }
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56
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57 lw_expr_stack_t *lw_expr_stack_dup(lw_expr_stack_t *s)
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58 {
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59 lw_expr_stack_node_t *t;
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60 lw_expr_stack_t *s2;
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61
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62 s2 = lw_expr_stack_create();
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63 for (t = s -> head; t; t = t -> next)
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64 {
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65 lw_expr_stack_push(s2, t -> term);
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66 }
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67 return s2;
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68 }
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69
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70 void lw_expr_term_free(lw_expr_term_t *t)
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71 {
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72 if (t)
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73 {
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74 if (t -> term_type == LW_TERM_SYM)
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75 lw_free(t -> symbol);
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76 lw_free(t);
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77 }
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78 }
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79
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80 lw_expr_term_t *lw_expr_term_create_oper(int oper)
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81 {
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82 lw_expr_term_t *t;
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83
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84 t = lw_malloc(sizeof(lw_expr_term_t));
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85 t -> term_type = LW_TERM_OPER;
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86 t -> value = oper;
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87 return t;
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88 }
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89
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90 lw_expr_term_t *lw_expr_term_create_int(int val)
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91 {
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92 lw_expr_term_t *t;
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93
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94 t = lw_malloc(sizeof(lw_expr_term_t));
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95 t -> term_type = LW_TERM_INT;
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96 t -> value = val;
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97 return t;
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98 }
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99
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100 lw_expr_term_t *lw_expr_term_create_sym(char *sym, int symtype)
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101 {
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102 lw_expr_term_t *t;
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103
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104 t = lw_malloc(sizeof(lw_expr_term_t));
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105 t -> term_type = LW_TERM_SYM;
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106 t -> symbol = lw_strdup(sym);
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107 t -> value = symtype;
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108 return t;
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109 }
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110
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111 lw_expr_term_t *lw_expr_term_dup(lw_expr_term_t *t)
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112 {
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113 switch (t -> term_type)
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114 {
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115 case LW_TERM_INT:
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116 return lw_expr_term_create_int(t -> value);
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117
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118 case LW_TERM_OPER:
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119 return lw_expr_term_create_oper(t -> value);
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120
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121 case LW_TERM_SYM:
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122 return lw_expr_term_create_sym(t -> symbol, t -> value);
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123
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124 default:
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125 exit(1);
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126 }
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127 // can't get here
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128 }
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129
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130 void lw_expr_stack_push(lw_expr_stack_t *s, lw_expr_term_t *t)
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131 {
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132 lw_expr_stack_node_t *n;
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133
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134 if (!s)
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135 {
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136 exit(1);
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137 }
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138
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139 n = lw_malloc(sizeof(lw_expr_stack_node_t));
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140 n -> next = NULL;
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141 n -> prev = s -> tail;
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142 n -> term = lw_expr_term_dup(t);
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143
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144 if (s -> head)
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145 {
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146 s -> tail -> next = n;
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147 s -> tail = n;
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148 }
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149 else
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150 {
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151 s -> head = n;
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152 s -> tail = n;
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153 }
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154 }
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155
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156 lw_expr_term_t *lw_expr_stack_pop(lw_expr_stack_t *s)
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157 {
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158 lw_expr_term_t *t;
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159 lw_expr_stack_node_t *n;
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160
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161 if (!(s -> tail))
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162 return NULL;
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163
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164 n = s -> tail;
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165 s -> tail = n -> prev;
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166 if (!(n -> prev))
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167 {
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168 s -> head = NULL;
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169 }
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170
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171 t = n -> term;
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172 n -> term = NULL;
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173
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174 lw_free(n);
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175
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176 return t;
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177 }
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178
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179 /*
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180 take an expression stack s and scan for operations that can be completed
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181
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182 return -1 on error, 0 on no error
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183
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184 possible errors are: division by zero or unknown operator
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185
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186 theory of operation:
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187
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188 scan the stack for an operator which has two constants preceding it (binary)
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189 or 1 constant preceding it (unary) and if found, perform the calculation
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190 and replace the operator and its operands with the result
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191
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192 repeat the scan until no futher simplications are found or if there are no
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193 further operators or only a single term remains
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194
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195 */
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196 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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197 {
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198 lw_expr_stack_node_t *n, *n2;
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199 lw_expr_stack_t *ss;
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200 int c;
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201
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202 next_iter_sym:
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203 // resolve symbols
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204 // symbols that do not resolve to an expression are left alone
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205 for (c = 0, n = s -> head; n; n = n -> next)
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206 {
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207 if (n -> term -> term_type == LW_TERM_SYM)
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208 {
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209 ss = sfunc(n -> term -> symbol, n -> term -> value, state);
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210 if (ss)
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211 {
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212 c++;
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213 // splice in the result stack
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214 if (n -> prev)
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215 {
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216 n -> prev -> next = ss -> head;
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217 }
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218 else
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219 {
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220 s -> head = ss -> head;
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221 }
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222 ss -> head -> prev = n -> prev;
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223 ss -> tail -> next = n -> next;
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224 if (n -> next)
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225 {
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226 n -> next -> prev = ss -> tail;
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227 }
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228 else
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229 {
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230 s -> tail = ss -> tail;
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231 }
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232 lw_expr_term_free(n -> term);
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233 lw_free(n);
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234 n = ss -> tail;
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235
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236 ss -> head = NULL;
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237 ss -> tail = NULL;
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238 lw_expr_stack_free(ss);
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239 }
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240 }
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241 }
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242 if (c)
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243 goto next_iter_sym;
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244
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245 next_iter:
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246 // a single term
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247 if (s -> head == s -> tail)
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248 return 0;
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249
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250 // search for an operator
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251 for (n = s -> head; n; n = n -> next)
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252 {
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253 if (n -> term -> term_type == LW_TERM_OPER)
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254 {
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255 if (n -> term -> value == LW_OPER_NEG
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256 || n -> term -> value == LW_OPER_COM
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257 )
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258 {
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259 // unary operator
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260 if (n -> prev && n -> prev -> term -> term_type == LW_TERM_INT)
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261 {
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262 // a unary operator we can resolve
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263 // we do the op then remove the term "n" is pointing at
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264 if (n -> term -> value == LW_OPER_NEG)
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265 {
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266 n -> prev -> term -> value = -(n -> prev -> term -> value);
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267 }
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268 else if (n -> term -> value == LW_OPER_COM)
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269 {
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270 n -> prev -> term -> value = ~(n -> prev -> term -> value);
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271 }
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272 n -> prev -> next = n -> next;
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273 if (n -> next)
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274 n -> next -> prev = n -> prev;
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275 else
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276 s -> tail = n -> prev;
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277
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278 lw_expr_term_free(n -> term);
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279 lw_free(n);
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280 break;
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281 }
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282 }
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283 else
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284 {
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285 // binary operator
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286 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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287 {
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288 // a binary operator we can resolve
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289 switch (n -> term -> value)
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290 {
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291 case LW_OPER_PLUS:
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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_MINUS:
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296 n -> prev -> prev -> term -> value -= n -> prev -> term -> value;
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297 break;
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298
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299 case LW_OPER_TIMES:
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300 n -> prev -> prev -> term -> value *= n -> prev -> term -> value;
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301 break;
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302
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303 case LW_OPER_DIVIDE:
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304 if (n -> prev -> term -> value == 0)
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305 return -1;
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306 n -> prev -> prev -> term -> value /= n -> prev -> term -> value;
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307 break;
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308
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309 case LW_OPER_MOD:
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310 if (n -> prev -> term -> value == 0)
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311 return -1;
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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_INTDIV:
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316 if (n -> prev -> term -> value == 0)
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317 return -1;
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318 n -> prev -> prev -> term -> value /= n -> prev -> term -> value;
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319 break;
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320
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321 case LW_OPER_BWAND:
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322 n -> prev -> prev -> term -> value &= n -> prev -> term -> value;
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323 break;
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324
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325 case LW_OPER_BWOR:
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326 n -> prev -> prev -> term -> value |= n -> prev -> term -> value;
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327 break;
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328
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329 case LW_OPER_BWXOR:
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330 n -> prev -> prev -> term -> value ^= n -> prev -> term -> value;
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331 break;
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332
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333 case LW_OPER_AND:
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334 n -> prev -> prev -> term -> value = (n -> prev -> term -> value && n -> prev -> prev -> term -> value) ? 1 : 0;
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335 break;
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336
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337 case LW_OPER_OR:
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338 n -> prev -> prev -> term -> value = (n -> prev -> term -> value || n -> prev -> prev -> term -> value) ? 1 : 0;
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339 break;
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340
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341 default:
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342 // return error if unknown operator!
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343 return -1;
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344 }
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345
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346 // now remove the two unneeded entries from the stack
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347 n -> prev -> prev -> next = n -> next;
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348 if (n -> next)
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349 n -> next -> prev = n -> prev -> prev;
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350 else
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351 s -> tail = n -> prev -> prev;
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352
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353 lw_expr_term_free(n -> term);
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354 lw_expr_term_free(n -> prev -> term);
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355 lw_free(n -> prev);
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356 lw_free(n);
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357 break;
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358 }
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359 }
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360 }
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361 }
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362 // note for the terminally confused about dynamic memory and pointers:
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363 // n will not be NULL even after the lw_free calls above so
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364 // this test will still work (n will be a dangling pointer)
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365 // (n will only be NULL if we didn't find any operators to simplify)
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366 if (n)
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367 goto next_iter;
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368
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369 return 0;
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370 }
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