lstring.c
(5.3.6)
/*
** $Id: lstring.c,v 2.56.1.1 2017/04/19 17:20:42 roberto Exp $
** String table (keeps all strings handled by Lua)
** See Copyright Notice in lua.h
*/
#define lstring_c
#define LUA_CORE
#include "lprefix.h"
#include <string.h>
#include "lua.h"
#include "ldebug.h"
#include "ldo.h"
#include "lmem.h"
#include "lobject.h"
#include "lstate.h"
#include "lstring.h"
#define MEMERRMSG "not enough memory"
/*
** 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->u.lnglen;
lua_assert(a->tt == LUA_TLNGSTR && b->tt == LUA_TLNGSTR);
return (a == b) || /* same instance or... */
((len == b->u.lnglen) && /* 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 step = (l >> LUAI_HASHLIMIT) + 1;
for (; l >= step; l -= step)
h ^= ((h<<5) + (h>>2) + cast_byte(str[l - 1]));
return h;
}
unsigned int luaS_hashlongstr (TString *ts) {
lua_assert(ts->tt == LUA_TLNGSTR);
if (ts->extra == 0) { /* no hash? */
ts->hash = luaS_hash(getstr(ts), ts->u.lnglen, ts->hash);
ts->extra = 1; /* now it has its hash */
}
return ts->hash;
}
/*
** 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->u.hnext; /* save next */
unsigned int h = lmod(p->hash, newsize); /* new position */
p->u.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;
}
/*
** Clear API string cache. (Entries cannot be empty, so fill them with
** a non-collectable string.)
*/
void luaS_clearcache (global_State *g) {
int i, j;
for (i = 0; i < STRCACHE_N; i++)
for (j = 0; j < STRCACHE_M; j++) {
if (iswhite(g->strcache[i][j])) /* will entry be collected? */
g->strcache[i][j] = g->memerrmsg; /* replace it with something fixed */
}
}
/*
** Initialize the string table and the string cache
*/
void luaS_init (lua_State *L) {
global_State *g = G(L);
int i, j;
luaS_resize(L, MINSTRTABSIZE); /* initial size of string table */
/* pre-create memory-error message */
g->memerrmsg = luaS_newliteral(L, MEMERRMSG);
luaC_fix(L, obj2gco(g->memerrmsg)); /* it should never be collected */
for (i = 0; i < STRCACHE_N; i++) /* fill cache with valid strings */
for (j = 0; j < STRCACHE_M; j++)
g->strcache[i][j] = g->memerrmsg;
}
/*
** creates a new string object
*/
static TString *createstrobj (lua_State *L, size_t l, int tag, unsigned int h) {
TString *ts;
GCObject *o;
size_t totalsize; /* total size of TString object */
totalsize = sizelstring(l);
o = luaC_newobj(L, tag, totalsize);
ts = gco2ts(o);
ts->hash = h;
ts->extra = 0;
getstr(ts)[l] = '\0'; /* ending 0 */
return ts;
}
TString *luaS_createlngstrobj (lua_State *L, size_t l) {
TString *ts = createstrobj(L, l, LUA_TLNGSTR, G(L)->seed);
ts->u.lnglen = l;
return ts;
}
void luaS_remove (lua_State *L, TString *ts) {
stringtable *tb = &G(L)->strt;
TString **p = &tb->hash[lmod(ts->hash, tb->size)];
while (*p != ts) /* find previous element */
p = &(*p)->u.hnext;
*p = (*p)->u.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)];
lua_assert(str != NULL); /* otherwise 'memcmp'/'memcpy' are undefined */
for (ts = *list; ts != NULL; ts = ts->u.hnext) {
if (l == ts->shrlen &&
(memcmp(str, getstr(ts), l * sizeof(char)) == 0)) {
/* found! */
if (isdead(g, ts)) /* dead (but not collected yet)? */
changewhite(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, l, LUA_TSHRSTR, h);
memcpy(getstr(ts), str, l * sizeof(char));
ts->shrlen = cast_byte(l);
ts->u.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 {
TString *ts;
if (l >= (MAX_SIZE - sizeof(TString))/sizeof(char))
luaM_toobig(L);
ts = luaS_createlngstrobj(L, l);
memcpy(getstr(ts), str, l * sizeof(char));
return ts;
}
}
/*
** Create or reuse a zero-terminated string, first checking in the
** cache (using the string address as a key). The cache can contain
** only zero-terminated strings, so it is safe to use 'strcmp' to
** check hits.
*/
TString *luaS_new (lua_State *L, const char *str) {
unsigned int i = point2uint(str) % STRCACHE_N; /* hash */
int j;
TString **p = G(L)->strcache[i];
for (j = 0; j < STRCACHE_M; j++) {
if (strcmp(str, getstr(p[j])) == 0) /* hit? */
return p[j]; /* that is it */
}
/* normal route */
for (j = STRCACHE_M - 1; j > 0; j--)
p[j] = p[j - 1]; /* move out last element */
/* new element is first in the list */
p[0] = luaS_newlstr(L, str, strlen(str));
return p[0];
}
Udata *luaS_newudata (lua_State *L, size_t s) {
Udata *u;
GCObject *o;
if (s > MAX_SIZE - sizeof(Udata))
luaM_toobig(L);
o = luaC_newobj(L, LUA_TUSERDATA, sizeludata(s));
u = gco2u(o);
u->len = s;
u->metatable = NULL;
setuservalue(L, u, luaO_nilobject);
return u;
}