commit e0306e386fdaa1b1f18f0c293a4b14de8b8a8536
parent 2e6e53c7ccb8634f21598b151413292c472ab432
Author: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Fri, 13 Feb 2015 11:05:09 -0200
some changes in 'hashfloat' to avoid undefined (in ISO C) numerical
conversions
Diffstat:
M | ltable.c | | | 29 | +++++++++++++++++++++-------- |
1 file changed, 21 insertions(+), 8 deletions(-)
diff --git a/ltable.c b/ltable.c
@@ -1,5 +1,5 @@
/*
-** $Id: ltable.c,v 2.100 2015/01/05 13:52:37 roberto Exp roberto $
+** $Id: ltable.c,v 2.101 2015/01/16 16:54:37 roberto Exp roberto $
** Lua tables (hash)
** See Copyright Notice in lua.h
*/
@@ -96,16 +96,29 @@ static int numisinteger (lua_Number x, lua_Integer *p) {
/*
-** hash for floating-point numbers
+** Hash for floating-point numbers.
+** The main computation should be just
+** n = frepx(n, &i); hash = (n * INT_MAX) + i
+** but there are some numerical subtleties.
+** In a two-complement representation, INT_MAX does not has an exact
+** representation as a float, but INT_MIN does; because the absolute
+** value of 'frexp' is smaller than 1 (unless 'n' is inf/NaN), the
+** absolute value of the product 'frexp * -INT_MIN' is smaller or equal
+** to INT_MAX. Next, the use of 'unsigned int' avoids overflows when
+** adding 'i'; the use of '~u' (instead of '-u') avoids problems with
+** INT_MIN.
*/
static Node *hashfloat (const Table *t, lua_Number n) {
int i;
- n = l_mathop(frexp)(n, &i) * cast_num(INT_MAX - DBL_MAX_EXP);
- i += cast_int(n);
- if (i < 0) {
- if (cast(unsigned int, i) == 0u - i) /* use unsigned to avoid overflows */
- i = 0; /* handle INT_MIN */
- i = -i; /* must be a positive value */
+ lua_Integer ni;
+ n = l_mathop(frexp)(n, &i) * -cast_num(INT_MIN);
+ if (!lua_numbertointeger(n, &ni)) { /* is 'n' inf/-inf/NaN? */
+ lua_assert(luai_numisnan(n) || l_mathop(fabs)(n) == HUGE_VAL);
+ i = 0;
+ }
+ else { /* normal case */
+ unsigned int u = cast(unsigned int, i) + cast(unsigned int, ni);
+ i = (u <= cast(unsigned int, INT_MAX) ? u : ~u);
}
return hashmod(t, i);
}