diff options
Diffstat (limited to 'lua/lstring.c')
-rw-r--r-- | lua/lstring.c | 115 |
1 files changed, 93 insertions, 22 deletions
diff --git a/lua/lstring.c b/lua/lstring.c index adec415..8b959f1 100644 --- a/lua/lstring.c +++ b/lua/lstring.c @@ -1,5 +1,5 @@ /* -** $Id: lstring.c,v 2.19 2011/05/03 16:01:57 roberto Exp $ +** $Id: lstring.c,v 2.24 2012/05/11 14:14:42 roberto Exp $ ** String table (keeps all strings handled by Lua) ** See Copyright Notice in lua.h */ @@ -18,7 +18,49 @@ #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 ^ 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; @@ -50,37 +92,49 @@ void luaS_resize (lua_State *L, int newsize) { } -static TString *newlstr (lua_State *L, const char *str, size_t l, - unsigned int h) { - size_t totalsize; /* total size of TString object */ - GCObject **list; /* (pointer to) list where it will be inserted */ +/* +** 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; - stringtable *tb = &G(L)->strt; - if (l+1 > (MAX_SIZET - sizeof(TString))/sizeof(char)) - luaM_toobig(L); - if (tb->nuse >= cast(lu_int32, tb->size) && tb->size <= MAX_INT/2) - luaS_resize(L, tb->size*2); /* too crowded */ + size_t totalsize; /* total size of TString object */ totalsize = sizeof(TString) + ((l + 1) * sizeof(char)); - list = &tb->hash[lmod(h, tb->size)]; - ts = &luaC_newobj(L, LUA_TSTRING, totalsize, list, 0)->ts; + ts = &luaC_newobj(L, tag, totalsize, list, 0)->ts; ts->tsv.len = l; ts->tsv.hash = h; - ts->tsv.reserved = 0; + ts->tsv.extra = 0; memcpy(ts+1, str, l*sizeof(char)); ((char *)(ts+1))[l] = '\0'; /* ending 0 */ - tb->nuse++; return ts; } -TString *luaS_newlstr (lua_State *L, const char *str, size_t l) { +/* +** 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; - unsigned int h = cast(unsigned int, l); /* seed */ - size_t step = (l>>5)+1; /* if string is too long, don't hash all its chars */ - size_t l1; - for (l1=l; l1>=step; l1-=step) /* compute hash */ - h = h ^ ((h<<5)+(h>>2)+cast(unsigned char, str[l1-1])); - for (o = G(L)->strt.hash[lmod(h, G(L)->strt.size)]; + 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); @@ -92,10 +146,27 @@ TString *luaS_newlstr (lua_State *L, const char *str, size_t l) { return ts; } } - return newlstr(L, str, l, h); /* not found; create a new string */ + 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)); } |