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Small optimizations in range checks

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Checks of the form '1 <= x && x <= M' were rewritten in the form
'(unsigned)x - 1 < (unsigned)M', which is usually more efficient.
(Other similar checks have similar translations.) Although
some compilers do these optimizations, that does not happen
for all compilers or all cases.
This commit is contained in:
Roberto Ierusalimschy
2019-03-27 14:56:10 -03:00
parent 0443ad9e28
commit d12262068d
4 changed files with 20 additions and 11 deletions
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8
ltablib.c
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@@ -69,7 +69,9 @@ static int tinsert (lua_State *L) {
case 3: {
lua_Integer i;
pos = luaL_checkinteger(L, 2); /* 2nd argument is the position */
luaL_argcheck(L, 1 <= pos && pos <= e, 2, "position out of bounds");
/* check whether 'pos' is in [1, e] */
luaL_argcheck(L, (lua_Unsigned)pos - 1u < (lua_Unsigned)e, 2,
"position out of bounds");
for (i = e; i > pos; i--) { /* move up elements */
lua_geti(L, 1, i - 1);
lua_seti(L, 1, i); /* t[i] = t[i - 1] */
@@ -89,7 +91,9 @@ static int tremove (lua_State *L) {
lua_Integer size = aux_getn(L, 1, TAB_RW);
lua_Integer pos = luaL_optinteger(L, 2, size);
if (pos != size) /* validate 'pos' if given */
luaL_argcheck(L, 1 <= pos && pos <= size + 1, 1, "position out of bounds");
/* check whether 'pos' is in [1, size + 1] */
luaL_argcheck(L, (lua_Unsigned)pos - 1u <= (lua_Unsigned)size, 1,
"position out of bounds");
lua_geti(L, 1, pos); /* result = t[pos] */
for ( ; pos < size; pos++) {
lua_geti(L, 1, pos + 1);