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Fix underflow in out of range check (#88)

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* Special case bool in cmp_less to avoid msvc's warnings

* Fix underflow in out of range check

The previous fix addressed bool but it seems that was not the heart
of the issue.

The problem is that (lhs - 1) can underflow.

Another example of the check trigger when it shouldn't is:
uint8_t with min_value set to 0 and a value of uint8_t::max
lhs-1 would underflow and find max (see added test).

The issue happens when lhs == rhs. To avoid that situation: flip the if-else!
`cmp_less(rhs, lhs)`means that rhs is strictly less than lhs, so
the check will not trigger when lhs == rhs.

Also, cleanup the bool special-case, as it is no longer necessary.

Note: for the bug to manifest, it is important that the min
of the enums is customized to be 0, so corresponding enum_range
specializations need to be present in the regression tests.
This commit is contained in:
Alexander Karatarakis 2021-06-25 05:00:54 -07:00 • committed by GitHub
parent b927151677
commit 41c916432b
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GPG key ID: 4AEE18F83AFDEB23
2 changed files with 51 additions and 8 deletions
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43
test/test.cpp
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@ -54,12 +54,30 @@ enum number : unsigned long {
#endif
};
enum class MaxUsedAsInvalid : std::uint8_t {
ONE,
TWO,
INVALID = std::numeric_limits<std::uint8_t>::max()
};
enum class Binary : bool {
ONE,
TWO
};
namespace magic_enum::customize {
template <>
struct enum_range<MaxUsedAsInvalid> {
static constexpr int min = 0;
static constexpr int max = 64;
};
template <>
struct enum_range<Binary> {
static constexpr int min = 0;
static constexpr int max = 64;
};
template <>
struct enum_range<number> {
static constexpr int min = 100;
@ -341,6 +359,9 @@ TEST_CASE("enum_values") {
constexpr auto& s5 = enum_values<Binary>();
REQUIRE(s5 == std::array<Binary, 2>{{Binary::ONE, Binary::TWO}});
constexpr auto& s6 = enum_values<MaxUsedAsInvalid>();
REQUIRE(s6 == std::array<MaxUsedAsInvalid, 2>{{MaxUsedAsInvalid::ONE, MaxUsedAsInvalid::TWO}});
}
TEST_CASE("enum_count") {
@ -358,6 +379,9 @@ TEST_CASE("enum_count") {
constexpr auto s5 = enum_count<Binary>();
REQUIRE(s5 == 2);
constexpr auto s6 = enum_count<MaxUsedAsInvalid>();
REQUIRE(s6 == 2);
}
TEST_CASE("enum_name") {
@ -427,6 +451,7 @@ TEST_CASE("enum_name") {
REQUIRE(enum_name<number::four>() == "four");
REQUIRE(enum_name<Binary::ONE>() == "ONE");
REQUIRE(enum_name<MaxUsedAsInvalid::ONE>() == "ONE");
}
}
@ -664,6 +689,9 @@ TEST_CASE("extrema") {
REQUIRE(magic_enum::detail::reflected_min_v<Binary> == 0);
REQUIRE(magic_enum::detail::min_v<Binary> == false);
REQUIRE(magic_enum::detail::reflected_min_v<MaxUsedAsInvalid> == 0);
REQUIRE(magic_enum::detail::min_v<MaxUsedAsInvalid> == 0);
}
SECTION("max") {
@ -689,6 +717,9 @@ TEST_CASE("extrema") {
REQUIRE(magic_enum::detail::reflected_max_v<Binary> == 1);
REQUIRE(magic_enum::detail::max_v<Binary> == true);
REQUIRE(magic_enum::detail::reflected_max_v<MaxUsedAsInvalid> == 64);
REQUIRE(magic_enum::detail::max_v<MaxUsedAsInvalid> == 1);
}
}
@ -755,4 +786,16 @@ TEST_CASE("cmp_less") {
REQUIRE_FALSE(cmp_less(uint32_t_min, int64_t_min + offset_int32_t));
REQUIRE_FALSE(cmp_less(uint64_t_min, int32_t_min + offset_int64_t));
}
SECTION("bool, right") {
REQUIRE(cmp_less(true, 5));
REQUIRE(cmp_less(false, 1));
REQUIRE_FALSE(cmp_less(false, -1));
}
SECTION("left, bool") {
REQUIRE_FALSE(cmp_less(5, true));
REQUIRE_FALSE(cmp_less(1, false));
REQUIRE(cmp_less(-1, false));
}
}