/*
** $Id: lstring.c,v 2.26 2013/01/08 13:50:10 roberto Exp $
** 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 "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 */
}


/*
** equality for strings
*/
int luaS_eqstr(TString *a, TString *b) {
    return (a->tsv.tt == b->tsv.tt) &&
           (a->tsv.tt == LUA_TSHRSTR ? eqshrstr(a, b) : luaS_eqlngstr(a, b));
}


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;
    /* cannot resize while GC is traversing strings */
    luaC_runtilstate(L, ~bitmask(GCSsweepstring));
    if (newsize > tb->size) {
        luaM_reallocvector(L, tb->hash, tb->size, newsize, GCObject *);
        for (i = tb->size; i < newsize; i++) tb->hash[i] = NULL;
    }
    /* rehash */
    for (i = 0; i < tb->size; i++) {
        GCObject *p = tb->hash[i];
        tb->hash[i] = NULL;
        while (p) {  /* for each node in the list */
            GCObject *next = gch(p)->next;  /* save next */
            unsigned int h = lmod(gco2ts(p)->hash, newsize);  /* new position */
            gch(p)->next = tb->hash[h];  /* chain it */
            tb->hash[h] = p;
            resetoldbit(p);  /* see MOVE OLD rule */
            p = next;
        }
    }
    if (newsize < tb->size) {
        /* shrinking slice must be empty */
        lua_assert(tb->hash[newsize] == NULL && tb->hash[tb->size - 1] == NULL);
        luaM_reallocvector(L, tb->hash, tb->size, newsize, GCObject *);
    }
    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, GCObject **list) {
    TString *ts;
    size_t totalsize;  /* total size of TString object */
    totalsize = sizeof(TString) + ((l + 1) * sizeof(char));
    ts = &luaC_newobj(L, tag, totalsize, list, 0)->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;
}


/*
** creates a new short string, inserting it into string table
*/
static TString *newshrstr(lua_State *L, const char *str, size_t l,
                          unsigned int h) {
    GCObject **list;  /* (pointer to) list where it will be inserted */
    stringtable *tb = &G(L)->strt;
    TString *s;
    if (tb->nuse >= cast(lu_int32, tb->size) && tb->size <= MAX_INT / 2)
        luaS_resize(L, tb->size * 2); /* too crowded */
    list = &tb->hash[lmod(h, tb->size)];
    s = createstrobj(L, str, l, LUA_TSHRSTR, h, list);
    tb->nuse++;
    return s;
}


/*
** 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) {
    GCObject *o;
    global_State *g = G(L);
    unsigned int h = luaS_hash(str, l, g->seed);
    for (o = g->strt.hash[lmod(h, g->strt.size)];
            o != NULL;
            o = gch(o)->next) {
        TString *ts = rawgco2ts(o);
        if (h == ts->tsv.hash &&
                l == ts->tsv.len &&
                (memcmp(str, getstr(ts), l * sizeof(char)) == 0)) {
            if (isdead(G(L), o))  /* string is dead (but was not collected yet)? */
                changewhite(o);  /* resurrect it */
            return ts;
        }
    }
    return newshrstr(L, str, l, h);  /* not found; create a new string */
}


/*
** 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_SIZET - sizeof(TString)) / sizeof(char))
            luaM_toobig(L);
        return createstrobj(L, str, l, LUA_TLNGSTR, G(L)->seed, NULL);
    }
}


/*
** 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, Table *e) {
    Udata *u;
    if (s > MAX_SIZET - sizeof(Udata))
        luaM_toobig(L);
    u = &luaC_newobj(L, LUA_TUSERDATA, sizeof(Udata) + s, NULL, 0)->u;
    u->uv.len = s;
    u->uv.metatable = NULL;
    u->uv.env = e;
    return u;
}

