symbol.c

四皇后问题

/*
	Little Smalltalk

		symbol creation - symbols are never deleted once created.
		timothy a. budd, 10/84
*/
/*
	The source code for the Little Smalltalk System may be freely
	copied provided that the source of all files is acknowledged
	and that this condition is copied with each file.

	The Little Smalltalk System is distributed without responsibility
	for the performance of the program and without any guarantee of
	maintenance.

	All questions concerning Little Smalltalk should be addressed to:

		Professor Tim Budd
		Department of Computer Science
		Oregon State University
		Corvallis, Oregon
		97331
		USA
*/
# include <stdio.h>
# include "object.h"
# include "symbol.h"

/*
	only one copy of symbol values are kept.
	multiple copies of the same symbol point to the same
	location.
	sy_search will find, and if necessary insert, a string into
	this common table 
*/

extern char x_str[];		/* initialized common string table */
extern symbol *x_tab[];		/* initialized common symbols table */
extern int x_tmax;		/* top of symbols table */
extern char *walloc();		/* routine to allocate a new word */
int ca_sym = 0;			/* symbol allocation counter */

/* sy_search performs a binary search of a symbol, is the main interface to
the symbols routines */
symbol *sy_search(word, insert)
char *word;
int  insert;
{	register int i;
	register int j;
	register int k;
	char *p;
	symbol *new_y();

	for (i=1; i <= x_tmax; i <<= 1);
	for (i >>= 1, j = i >>1, i--; ; j >>= 1) {
		p = symbol_value(x_tab[i]);
		if (word == p) return(x_tab[i]);
		k = *word - *p;
		if (!k) k = *(word+1) - *(p+1);
		if (!k) k = strcmp(word, p);
		if (!k)
			return(x_tab[i]);
		if (!j) break;
		if (k < 0) i -= j;
		else {
			if ((i += j) > x_tmax) i = x_tmax;
			}
		}
	if (insert) {
		if (k > 0) i++;
		if ((k = ++x_tmax) >= SYMTABMAX)
			cant_happen(12);
		for (; k > i; k--) {
			x_tab[k] = x_tab[k-1];
			}
		/*fprintf(stderr,"adding %s\n", word);*/
		x_tab[i] = new_y(walloc(word));
		x_tab[i]->y_ref_count++; /* make sure not freed */
		return(x_tab[i]);
		}
	else return((symbol *) 0);
}

/* w_search performs a search for a word, not a symbol */
char *w_search(word, insert)
char *word;
int insert;
{	symbol *sym;

	sym = sy_search(word, insert);
	if (sym)
		return(symbol_value(sym));
	else
		return((char *) 0);
}

/*---------------------------------------*/

static mstruct *fr_symbol = 0;		/* symbols free list */
static symbol strspace[SYMINITSIZE];	/* initial symbols free list */

extern object *o_object;		/* common instance of Object */
extern class *ArrayedCollection;

/* sym_init - initialize the symbols routine */
sym_init() {
	int  i;
	symbol *p;
	mstruct   *new;

	p = strspace;
	for (i = 0; i < SYMINITSIZE; i++) {
		new = (mstruct *) p;
		new->mlink = fr_symbol;
		fr_symbol = new;
		p++;
		}
}

/* new_y is the internal routine for making new symbols */
symbol *new_y(text)
char *text;
{	symbol *new;

	if (fr_symbol) {
		new = (symbol *) fr_symbol;
		fr_symbol = fr_symbol->mlink;
		}
	else {
		ca_sym++;
		new = structalloc(symbol);
		}

	new->y_ref_count = 0;
	new->y_size = SYMBOLSIZE;
	new->y_value = text;
	return(new);
}