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LibCrypto: Add a constructor to (Un)SignedBigInteger taking a double

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For now this will assume that the double given is exactly representable
as an integer, so no NaN, infinity or rounding.
This commit is contained in:
davidot 2022-08-25 23:37:09 +02:00 • committed by Linus Groh
parent c87d10365b
commit 528891bf69
5 changed files with 161 additions and 8 deletions
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74
Tests/LibCrypto/TestBigInteger.cpp
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@ -864,6 +864,80 @@ TEST_CASE(to_double)
#undef EXPECT_TO_EQUAL_DOUBLE
}
TEST_CASE(bigint_from_double)
{
{
Crypto::UnsignedBigInteger from_zero { 0.0 };
EXPECT(from_zero.is_zero());
EXPECT(!from_zero.is_invalid());
}
#define SURVIVES_ROUND_TRIP_UNSIGNED(double_value) \
{ \
Crypto::UnsignedBigInteger bigint { (double_value) }; \
EXPECT_EQ(bigint.to_double(), (double_value)); \
}
SURVIVES_ROUND_TRIP_UNSIGNED(0.0);
SURVIVES_ROUND_TRIP_UNSIGNED(1.0);
SURVIVES_ROUND_TRIP_UNSIGNED(100000.0);
SURVIVES_ROUND_TRIP_UNSIGNED(1000000000000.0);
SURVIVES_ROUND_TRIP_UNSIGNED(10000000000000000000.0);
SURVIVES_ROUND_TRIP_UNSIGNED(NumericLimits<double>::max());
SURVIVES_ROUND_TRIP_UNSIGNED(bit_cast<double>(0x4340000000000002ULL));
SURVIVES_ROUND_TRIP_UNSIGNED(bit_cast<double>(0x4340000000000001ULL));
SURVIVES_ROUND_TRIP_UNSIGNED(bit_cast<double>(0x4340000000000000ULL));
// Failed on last bits of mantissa
SURVIVES_ROUND_TRIP_UNSIGNED(bit_cast<double>(0x7EDFFFFFFFFFFFFFULL));
SURVIVES_ROUND_TRIP_UNSIGNED(bit_cast<double>(0x7ed5555555555555ULL));
SURVIVES_ROUND_TRIP_UNSIGNED(bit_cast<double>(0x7EDCBA9876543210ULL));
// Has exactly exponent of 32
SURVIVES_ROUND_TRIP_UNSIGNED(bit_cast<double>(0x41f22f74e0000000ULL));
#define SURVIVES_ROUND_TRIP_SIGNED(double_value) \
{ \
Crypto::SignedBigInteger bigint_positive { (double_value) }; \
EXPECT_EQ(bigint_positive.to_double(), (double_value)); \
Crypto::SignedBigInteger bigint_negative { -(double_value) }; \
EXPECT_EQ(bigint_negative.to_double(), -(double_value)); \
EXPECT(bigint_positive != bigint_negative); \
bigint_positive.negate(); \
EXPECT(bigint_positive == bigint_negative); \
}
{
// Negative zero should be converted to positive zero
double const negative_zero = bit_cast<double>(0x8000000000000000);
// However it should give a bit exact +0.0
Crypto::SignedBigInteger from_negative_zero { negative_zero };
EXPECT(from_negative_zero.is_zero());
EXPECT(!from_negative_zero.is_negative());
double result = from_negative_zero.to_double();
EXPECT_EQ(result, 0.0);
EXPECT_EQ(bit_cast<u64>(result), 0ULL);
}
SURVIVES_ROUND_TRIP_SIGNED(1.0);
SURVIVES_ROUND_TRIP_SIGNED(100000.0);
SURVIVES_ROUND_TRIP_SIGNED(-1000000000000.0);
SURVIVES_ROUND_TRIP_SIGNED(10000000000000000000.0);
SURVIVES_ROUND_TRIP_SIGNED(NumericLimits<double>::max());
SURVIVES_ROUND_TRIP_SIGNED(NumericLimits<double>::lowest());
SURVIVES_ROUND_TRIP_SIGNED(bit_cast<double>(0x4340000000000002ULL));
SURVIVES_ROUND_TRIP_SIGNED(bit_cast<double>(0x4340000000000001ULL));
SURVIVES_ROUND_TRIP_SIGNED(bit_cast<double>(0x4340000000000000ULL));
SURVIVES_ROUND_TRIP_SIGNED(bit_cast<double>(0x7EDFFFFFFFFFFFFFULL));
SURVIVES_ROUND_TRIP_SIGNED(bit_cast<double>(0x7ed5555555555555ULL));
SURVIVES_ROUND_TRIP_SIGNED(bit_cast<double>(0x7EDCBA9876543210ULL));
#undef SURVIVES_ROUND_TRIP_SIGNED
#undef SURVIVES_ROUND_TRIP_UNSIGNED
}
namespace AK {
template<>