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some changes in 'hashfloat' to avoid undefined (in ISO C) numerical

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This commit is contained in:
Roberto Ierusalimschy 2015-02-13 11:05:34 -02:00
parent 2e6e53c7cc
commit e0306e386f
1 changed files with 21 additions and 8 deletions
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29
ltable.c
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@ -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);
}