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145 行
4.1 KiB
145 行
4.1 KiB
%{
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/* compile: leg -o calc.c calc.leg
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* cc -o calc calc.c
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*
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* run: echo "2+3" | ./calc
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*/
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#include <stdbool.h>
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#include <sysexits.h>
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union u_t {
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int ival;
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char *sval;
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};
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#define YYSTYPE union u_t
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YYSTYPE yylval;
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#define SYMBOL_TABLE_CHUNK 1024
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typedef struct symbol_t {
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char *ident;
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bool defined;
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int value;
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} symbol_t;
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typedef struct table_t {
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symbol_t **array;
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size_t size; // size_t allows your table to grow past the 1G element limit of a 32-bit number on 64-bit machines
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size_t capacity;
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} table_t;
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#define TABLE_INITIALISER { NULL, 0, 0 } // first call to table_insert() will initialise storage
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table_t table = TABLE_INITIALISER; // safe but not strictly needed on Unix because BSS segment is initialised to all zeroes
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void *memcheck(void *ptr)
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{
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if (NULL == ptr) {
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fprintf(stderr, "Error: out of memory\n");
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exit(EX_OSERR); // this is as close as we have for 'resource unavailable'
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}
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return ptr;
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}
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ssize_t table_search(table_t *table, char *ident)
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{
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ssize_t l = 0, r = table->size - 1; // no longer needed as parameters if we pass a table as the first parameter
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while (l <= r) { // swapped the order of l and r because I always visualise data as laid out from left-to-right ;-)
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ssize_t mid = (l + r) / 2;
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int cmpres= strcmp(table->array[mid]->ident, ident);
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if (cmpres > 0) r = mid - 1;
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else if (cmpres < 0) l = mid + 1;
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else return mid; // non-negative result => element found at this index
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}
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return -1 - l; // negative result => 'not found', reflected around -1 instead of 0 to allow 'not found' at index 0
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}
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ssize_t table_insert(table_t *table, symbol_t *element, size_t pos)
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{
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if (pos > table->size) { // don't need to check for pos < 0 because size_t is unsigned
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return -1;
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}
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if (table->size >= table->capacity) {
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// on the first call table->array will be NULL and realloc() will behave like malloc()
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table->array = memcheck(realloc(table->array, sizeof(symbol_t *) * (table->capacity + SYMBOL_TABLE_CHUNK)));
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table->capacity += SYMBOL_TABLE_CHUNK;
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}
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memmove(table->array + pos + 1, table->array + pos, sizeof(*table->array) * (table->size - pos));
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table->array[pos] = element;
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return ++(table->size);
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}
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symbol_t *intern(char *ident, bool create)
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{
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ssize_t res = table_search(&table, ident); // < 0 => not found
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if (res >= 0) return table.array[res];
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if (!create) return NULL;
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res= -1 - res; // 'un-negate' the resulr by reflecting it around X=-1
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symbol_t *new_symbol = memcheck(calloc(1, sizeof(symbol_t))); // calloc() will init all content to 0 (including .value member)
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new_symbol->ident = memcheck(strdup(ident)); // check for out-of-memory
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new_symbol->defined = false; // implicit in calloc(), but safer to do it explicitly anyway
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table_insert(&table, new_symbol, res);
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return new_symbol;
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}
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symbol_t *update_value(symbol_t * s, int value)
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{
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s->value = value;
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s->defined = true;
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return s;
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}
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char *ident_buf;
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%}
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start = e:exp { yylval = e }
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exp = - (a:assign { $$ = a }
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| s:sum { $$ = s }
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)
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assign = l:IDENT { ident_buf = strdup(l.sval) }
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EQUAL n:sum { symbol_t *nsymb = intern(ident_buf, true); $$.ival = update_value(nsymb, n.ival)->value; free(ident_buf) }
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sum = PLUS* l:prod
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( PLUS+ r:prod { l.ival += r.ival }
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| MINUS r:prod { l.ival -= r.ival }
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)* { $$.ival = l.ival }
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prod = l:neg
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( MULTI r:neg { l.ival *= r.ival }
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| DIVIDE r:neg { l.ival /= r.ival }
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| MODULO r:neg { l.ival %= r.ival }
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)* { $$.ival = l.ival }
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neg = MINUS n:neg { $$.ival = -n.ival }
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| n:value { $$.ival = n.ival }
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value = n:NUMBER { $$.ival = n.ival }
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| l:IDENT { symbol_t *fsymb = intern(l.sval, false); $$.ival = (fsymb != NULL) ? (fsymb->defined == true) ? fsymb->value : 0 : 0 }
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- = [ \t]*
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NUMBER = < [0-9]+ > - { $$.ival = atoi(yytext) }
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PLUS = '+' -
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MINUS = '-' -
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MULTI = '*' -
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DIVIDE = '/' -
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MODULO = '%' -
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EQUAL = '=' -
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IDENT = < [a-zA-Z]+ > - { $$.sval = yytext }
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%%
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int main(int argc, char **argv)
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{
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while (yyparse()) {
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printf("%d\n", yylval.ival);
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}
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return 0;
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}
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