lua/lstring.c

177 lines
4.5 KiB
C

/*
** $Id: lstring.c,v 2.38 2014/03/19 18:51:42 roberto Exp roberto $
** String table (keeps all strings handled by Lua)
** See Copyright Notice in lua.h
*/
#include <string.h>
#define lstring_c
#define LUA_CORE
#include "lua.h"
#include "ldebug.h"
#include "ldo.h"
#include "lmem.h"
#include "lobject.h"
#include "lstate.h"
#include "lstring.h"
/*
** Lua will use at most ~(2^LUAI_HASHLIMIT) bytes from a string to
** compute its hash
*/
#if !defined(LUAI_HASHLIMIT)
#define LUAI_HASHLIMIT 5
#endif
/*
** equality for long strings
*/
int luaS_eqlngstr (TString *a, TString *b) {
size_t len = a->tsv.len;
lua_assert(a->tsv.tt == LUA_TLNGSTR && b->tsv.tt == LUA_TLNGSTR);
return (a == b) || /* same instance or... */
((len == b->tsv.len) && /* equal length and ... */
(memcmp(getstr(a), getstr(b), len) == 0)); /* equal contents */
}
unsigned int luaS_hash (const char *str, size_t l, unsigned int seed) {
unsigned int h = seed ^ cast(unsigned int, l);
size_t l1;
size_t step = (l >> LUAI_HASHLIMIT) + 1;
for (l1 = l; l1 >= step; l1 -= step)
h = h ^ ((h<<5) + (h>>2) + cast_byte(str[l1 - 1]));
return h;
}
/*
** resizes the string table
*/
void luaS_resize (lua_State *L, int newsize) {
int i;
stringtable *tb = &G(L)->strt;
if (newsize > tb->size) { /* grow table if needed */
luaM_reallocvector(L, tb->hash, tb->size, newsize, TString *);
for (i = tb->size; i < newsize; i++)
tb->hash[i] = NULL;
}
for (i = 0; i < tb->size; i++) { /* rehash */
TString *p = tb->hash[i];
tb->hash[i] = NULL;
while (p) { /* for each node in the list */
TString *hnext = p->tsv.hnext; /* save next */
unsigned int h = lmod(p->tsv.hash, newsize); /* new position */
p->tsv.hnext = tb->hash[h]; /* chain it */
tb->hash[h] = p;
p = hnext;
}
}
if (newsize < tb->size) { /* shrink table if needed */
/* vanishing slice should be empty */
lua_assert(tb->hash[newsize] == NULL && tb->hash[tb->size - 1] == NULL);
luaM_reallocvector(L, tb->hash, tb->size, newsize, TString *);
}
tb->size = newsize;
}
/*
** creates a new string object
*/
static TString *createstrobj (lua_State *L, const char *str, size_t l,
int tag, unsigned int h) {
TString *ts;
size_t totalsize; /* total size of TString object */
totalsize = sizeof(TString) + ((l + 1) * sizeof(char));
ts = &luaC_newobj(L, tag, totalsize)->ts;
ts->tsv.len = l;
ts->tsv.hash = h;
ts->tsv.extra = 0;
memcpy(ts+1, str, l*sizeof(char));
((char *)(ts+1))[l] = '\0'; /* ending 0 */
return ts;
}
void luaS_remove (lua_State *L, TString *ts) {
stringtable *tb = &G(L)->strt;
TString **p = &tb->hash[lmod(ts->tsv.hash, tb->size)];
while (*p != ts) /* find previous element */
p = &(*p)->tsv.hnext;
*p = (*p)->tsv.hnext; /* remove element from its list */
tb->nuse--;
}
/*
** checks whether short string exists and reuses it or creates a new one
*/
static TString *internshrstr (lua_State *L, const char *str, size_t l) {
TString *ts;
global_State *g = G(L);
unsigned int h = luaS_hash(str, l, g->seed);
TString **list = &g->strt.hash[lmod(h, g->strt.size)];
for (ts = *list; ts != NULL; ts = ts->tsv.hnext) {
if (l == ts->tsv.len &&
(memcmp(str, getstr(ts), l * sizeof(char)) == 0)) {
/* found! */
if (isdead(g, obj2gco(ts))) /* dead (but not collected yet)? */
changewhite(obj2gco(ts)); /* resurrect it */
return ts;
}
}
if (g->strt.nuse >= g->strt.size && g->strt.size <= MAX_INT/2) {
luaS_resize(L, g->strt.size * 2);
list = &g->strt.hash[lmod(h, g->strt.size)]; /* recompute with new size */
}
ts = createstrobj(L, str, l, LUA_TSHRSTR, h);
ts->tsv.hnext = *list;
*list = ts;
g->strt.nuse++;
return ts;
}
/*
** new string (with explicit length)
*/
TString *luaS_newlstr (lua_State *L, const char *str, size_t l) {
if (l <= LUAI_MAXSHORTLEN) /* short string? */
return internshrstr(L, str, l);
else {
if (l + 1 > (MAX_SIZE - sizeof(TString))/sizeof(char))
luaM_toobig(L);
return createstrobj(L, str, l, LUA_TLNGSTR, G(L)->seed);
}
}
/*
** new zero-terminated string
*/
TString *luaS_new (lua_State *L, const char *str) {
return luaS_newlstr(L, str, strlen(str));
}
Udata *luaS_newudata (lua_State *L, size_t s) {
Udata *u;
if (s > MAX_SIZE - sizeof(Udata))
luaM_toobig(L);
u = &luaC_newobj(L, LUA_TUSERDATA, sizeof(Udata) + s)->u;
u->uv.len = s;
u->uv.metatable = NULL;
setuservalue(L, u, luaO_nilobject);
return u;
}