mirrors
/
lua
mirror of https://github.com/lua/lua
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

Short strings always use all bytes in the hash 

Collisions in short strings occurr just by their existence, when
internalizing them. (Collisions in long strings is caused/controlled
by the program, when adding them as keys to the same table.)
This commit is contained in:
Roberto Ierusalimschy 2020-04-01 10:52:41 -03:00
parent 513559cc47
commit 7288528a1e
3 changed files with 10 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
lstate.c
View File

@ -76,7 +76,7 @@ static unsigned int luai_makeseed (lua_State *L) {
addbuff(buff, p, &h); /* local variable */
addbuff(buff, p, &lua_newstate); /* public function */
lua_assert(p == sizeof(buff));
return luaS_hash(buff, p, h);
return luaS_hash(buff, p, h, 1);
}
#endif

12
lstring.c
View File

@ -23,7 +23,7 @@
/*
** Lua will use at most ~(2^LUAI_HASHLIMIT) bytes from a string to
** Lua will use at most ~(2^LUAI_HASHLIMIT) bytes from a long string to
** compute its hash
*/
#if !defined(LUAI_HASHLIMIT)
@ -50,9 +50,9 @@ int luaS_eqlngstr (TString *a, TString *b) {
}
unsigned int luaS_hash (const char *str, size_t l, unsigned int seed) {
unsigned int luaS_hash (const char *str, size_t l, unsigned int seed,
size_t step) {
unsigned int h = seed ^ cast_uint(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;
@ -62,7 +62,9 @@ unsigned int luaS_hash (const char *str, size_t l, unsigned int seed) {
unsigned int luaS_hashlongstr (TString *ts) {
lua_assert(ts->tt == LUA_VLNGSTR);
if (ts->extra == 0) { /* no hash? */
ts->hash = luaS_hash(getstr(ts), ts->u.lnglen, ts->hash);
size_t len = ts->u.lnglen;
size_t step = (len >> LUAI_HASHLIMIT) + 1;
ts->hash = luaS_hash(getstr(ts), len, ts->hash, step);
ts->extra = 1; /* now it has its hash */
}
return ts->hash;
@ -199,7 +201,7 @@ static TString *internshrstr (lua_State *L, const char *str, size_t l) {
TString *ts;
global_State *g = G(L);
stringtable *tb = &g->strt;
unsigned int h = luaS_hash(str, l, g->seed);
unsigned int h = luaS_hash(str, l, g->seed, 1);
TString **list = &tb->hash[lmod(h, tb->size)];
lua_assert(str != NULL); /* otherwise 'memcmp'/'memcpy' are undefined */
for (ts = *list; ts != NULL; ts = ts->u.hnext) {

3
lstring.h
View File

@ -37,7 +37,8 @@
#define eqshrstr(a,b) check_exp((a)->tt == LUA_VSHRSTR, (a) == (b))
LUAI_FUNC unsigned int luaS_hash (const char *str, size_t l, unsigned int seed);
LUAI_FUNC unsigned int luaS_hash (const char *str, size_t l,
unsigned int seed, size_t step);
LUAI_FUNC unsigned int luaS_hashlongstr (TString *ts);
LUAI_FUNC int luaS_eqlngstr (TString *a, TString *b);
LUAI_FUNC void luaS_resize (lua_State *L, int newsize);