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`getn' uses binary search if it has to count elements

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This commit is contained in:
Roberto Ierusalimschy 2004-06-02 16:06:14 -03:00
parent f4718544de
commit b8691f13a8
1 changed files with 27 additions and 8 deletions
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35
lauxlib.c
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@ -1,5 +1,5 @@
/*
** $Id: lauxlib.c,v 1.113 2004/05/31 19:27:14 roberto Exp roberto $
** $Id: lauxlib.c,v 1.114 2004/06/02 13:50:46 roberto Exp roberto $
** Auxiliary functions for building Lua libraries
** See Copyright Notice in lua.h
*/
@ -299,6 +299,31 @@ LUALIB_API void luaL_setn (lua_State *L, int t, int n) {
}
/* find an `n' such that t[n] ~= nil and t[n+1] == nil */
static int countn (lua_State *L, int t) {
int i = LUA_FIRSTINDEX - 1;
int j = 2;
/* find `i' such that i <= n < i*2 (= j) */
for (;;) {
lua_rawgeti(L, t, j);
if (lua_isnil(L, -1)) break;
lua_pop(L, 1);
i = j;
j = i*2;
}
lua_pop(L, 1);
/* i <= n < j; do a binary search */
while (i < j-1) {
int m = (i+j)/2;
lua_rawgeti(L, t, m);
if (lua_isnil(L, -1)) j = m;
else i = m;
lua_pop(L, 1);
}
return i - LUA_FIRSTINDEX + 1;
}
LUALIB_API int luaL_getn (lua_State *L, int t) {
int n;
t = abs_index(L, t);
@ -308,13 +333,7 @@ LUALIB_API int luaL_getn (lua_State *L, int t) {
if ((n = checkint(L, 2)) >= 0) return n;
lua_getfield(L, t, "n"); /* else try t.n */
if ((n = checkint(L, 1)) >= 0) return n;
for (n = LUA_FIRSTINDEX; ; n++) { /* else must count elements */
lua_rawgeti(L, t, n);
if (lua_isnil(L, -1)) break;
lua_pop(L, 1);
}
lua_pop(L, 1);
return n - LUA_FIRSTINDEX;
return countn(L, t);
}
/* }====================================================== */