Lua2RTT/lua-5.3.4/lstring.c

/*
** $Id: lstring.c,v 2.56 2015/11/23 11:32:51 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;
}