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Fix silent overflow in from_string() decimal parsing #370

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Fix silent overflow in from_string() decimal parsing #370

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6 changes: 4 additions & 2 deletions include/intx/intx.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -840,9 +840,11 @@ constexpr Int from_string(const char* str)
throw_<std::out_of_range>(str);

const auto d = from_dec_digit(c);
x = x * Int{10} + d;
if (x < d)
// Check for overflow before multiplying, since checking after could be fooled by
// wraparound.
if (x > (std::numeric_limits<Int>::max() - d) / Int{10})
throw_<std::out_of_range>(str);
x = x * Int{10} + d;
}
return x;
}
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9 changes: 9 additions & 0 deletions test/unittests/test_intx.cpp
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Expand Up @@ -348,6 +348,15 @@ TYPED_TEST(uint_test, string_conversions)
}
}

TYPED_TEST(uint_test, from_string_decimal_overflow)
{
// A decimal string with as many digits as TypeParam::max() but consisting of all 9s
// is always greater than max() and must be rejected, not silently wrapped around.
const auto digits = to_string(std::numeric_limits<TypeParam>::max()).size();
const auto s = std::string(digits, '9');
EXPECT_THROW_MESSAGE(from_string<TypeParam>(s), std::out_of_range, s.c_str());
}

TYPED_TEST(uint_test, to_string_base)
{
auto x = TypeParam{1024};
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