On Tue, Dec 18, 2018 at 2:31 PM, Ryosuke Niwa <rn...@webkit.org> wrote:
I tend to agree but then we'd come up with other numbers for the
empty & deleted values.
I've been thinking that we could use -1 and -2 but that's also
somewhat arbitrary restriction.
Using min/max values seems much safer. E.g. we already have in
HashTraits.h:
// Default unsigned traits disallow both 0 and max as keys -- use these
traits to allow zero and disallow max - 1.
template<typename T> struct UnsignedWithZeroKeyHashTraits :
GenericHashTraits<T> {
static const bool emptyValueIsZero = false;
static T emptyValue() { return std::numeric_limits<T>::max(); }
static void constructDeletedValue(T& slot) { slot =
std::numeric_limits<T>::max() - 1; }
static bool isDeletedValue(T value) { return value ==
std::numeric_limits<T>::max() - 1; }
};
And:
template<typename T> struct SignedWithZeroKeyHashTraits :
GenericHashTraits<T> {
static const bool emptyValueIsZero = false;
static T emptyValue() { return std::numeric_limits<T>::min(); }
static void constructDeletedValue(T& slot) { slot =
std::numeric_limits<T>::max(); }
static bool isDeletedValue(T value) { return value ==
std::numeric_limits<T>::max(); }
};
Which both seem much safer than the current default:
// Default integer traits disallow both 0 and -1 as keys (max value
instead of -1 for unsigned).
template<typename T> struct GenericHashTraitsBase<true, T> :
GenericHashTraitsBase<false, T> {
static const bool emptyValueIsZero = true;
static void constructDeletedValue(T& slot) { slot =
static_cast<T>(-1); }
static bool isDeletedValue(T value) { return value ==
static_cast<T>(-1); }
};
Michael
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