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LibCrypto: Add a way to compare a SignedBigInteger with a double

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This supports any double value (except for NaNs) instead of having to
cast the double to some smaller type which doesn't work for very large
values.
This commit is contained in:
davidot 2022-08-19 23:45:36 +02:00 • committed by Linus Groh
parent 14264ca022
commit b5c00830c2
3 changed files with 271 additions and 1 deletions
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113
Tests/LibCrypto/TestBigInteger.cpp
View file

@ -9,7 +9,7 @@
#include <LibCrypto/BigInt/UnsignedBigInteger.h>
#include <LibCrypto/NumberTheory/ModularFunctions.h>
#include <LibTest/TestCase.h>
#include <cstring>
#include <math.h>
static Crypto::UnsignedBigInteger bigint_fibonacci(size_t n)
{
@ -658,3 +658,114 @@ TEST_CASE(test_negative_zero_is_not_allowed)
EXPECT(zero.unsigned_value().is_zero());
EXPECT(!zero.is_negative());
}
TEST_CASE(double_comparisons)
{
#define EXPECT_LESS_THAN(bigint, double_value) EXPECT_EQ(bigint.compare_to_double(double_value), Crypto::SignedBigInteger::CompareResult::DoubleGreaterThanBigInt)
#define EXPECT_GREATER_THAN(bigint, double_value) EXPECT_EQ(bigint.compare_to_double(double_value), Crypto::SignedBigInteger::CompareResult::DoubleLessThanBigInt)
#define EXPECT_EQUAL_TO(bigint, double_value) EXPECT_EQ(bigint.compare_to_double(double_value), Crypto::SignedBigInteger::CompareResult::DoubleEqualsBigInt)
{
Crypto::SignedBigInteger zero { 0 };
EXPECT_EQUAL_TO(zero, 0.0);
EXPECT_EQUAL_TO(zero, -0.0);
}
{
Crypto::SignedBigInteger one { 1 };
EXPECT_EQUAL_TO(one, 1.0);
EXPECT_GREATER_THAN(one, -1.0);
EXPECT_GREATER_THAN(one, 0.5);
EXPECT_GREATER_THAN(one, -0.5);
EXPECT_LESS_THAN(one, 1.000001);
one.negate();
auto const& negative_one = one;
EXPECT_EQUAL_TO(negative_one, -1.0);
EXPECT_LESS_THAN(negative_one, 1.0);
EXPECT_LESS_THAN(one, 0.5);
EXPECT_LESS_THAN(one, -0.5);
EXPECT_GREATER_THAN(one, -1.5);
EXPECT_LESS_THAN(one, 1.000001);
EXPECT_GREATER_THAN(one, -1.000001);
}
{
double double_max_value = NumericLimits<double>::max();
double double_below_max_value = nextafter(double_max_value, 0.0);
VERIFY(double_below_max_value < double_max_value);
VERIFY(double_below_max_value < (double_max_value - 1.0));
auto max_value_in_bigint = Crypto::SignedBigInteger::from_base(16, "fffffffffffff800000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"sv);
auto max_value_plus_one = max_value_in_bigint.plus(Crypto::SignedBigInteger { 1 });
auto max_value_minus_one = max_value_in_bigint.minus(Crypto::SignedBigInteger { 1 });
auto below_max_value_in_bigint = Crypto::SignedBigInteger::from_base(16, "fffffffffffff000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"sv);
EXPECT_EQUAL_TO(max_value_in_bigint, double_max_value);
EXPECT_LESS_THAN(max_value_minus_one, double_max_value);
EXPECT_GREATER_THAN(max_value_plus_one, double_max_value);
EXPECT_LESS_THAN(below_max_value_in_bigint, double_max_value);
EXPECT_GREATER_THAN(max_value_in_bigint, double_below_max_value);
EXPECT_GREATER_THAN(max_value_minus_one, double_below_max_value);
EXPECT_GREATER_THAN(max_value_plus_one, double_below_max_value);
EXPECT_EQUAL_TO(below_max_value_in_bigint, double_below_max_value);
}
{
double double_min_value = NumericLimits<double>::lowest();
double double_above_min_value = nextafter(double_min_value, 0.0);
VERIFY(double_above_min_value > double_min_value);
VERIFY(double_above_min_value > (double_min_value + 1.0));
auto min_value_in_bigint = Crypto::SignedBigInteger::from_base(16, "-fffffffffffff800000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"sv);
auto min_value_plus_one = min_value_in_bigint.plus(Crypto::SignedBigInteger { 1 });
auto min_value_minus_one = min_value_in_bigint.minus(Crypto::SignedBigInteger { 1 });
auto above_min_value_in_bigint = Crypto::SignedBigInteger::from_base(16, "-fffffffffffff000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"sv);
EXPECT_EQUAL_TO(min_value_in_bigint, double_min_value);
EXPECT_LESS_THAN(min_value_minus_one, double_min_value);
EXPECT_GREATER_THAN(min_value_plus_one, double_min_value);
EXPECT_GREATER_THAN(above_min_value_in_bigint, double_min_value);
EXPECT_LESS_THAN(min_value_in_bigint, double_above_min_value);
EXPECT_LESS_THAN(min_value_minus_one, double_above_min_value);
EXPECT_LESS_THAN(min_value_plus_one, double_above_min_value);
EXPECT_EQUAL_TO(above_min_value_in_bigint, double_above_min_value);
}
{
double just_above_255 = bit_cast<double>(0x406fe00000000001ULL);
double just_below_255 = bit_cast<double>(0x406fdfffffffffffULL);
double double_255 = 255.0;
Crypto::SignedBigInteger bigint_255 { 255 };
EXPECT_EQUAL_TO(bigint_255, double_255);
EXPECT_GREATER_THAN(bigint_255, just_below_255);
EXPECT_LESS_THAN(bigint_255, just_above_255);
}
#undef EXPECT_LESS_THAN
#undef EXPECT_GREATER_THAN
#undef EXPECT_EQUAL_TO
}
namespace AK {
template<>
struct Formatter<Crypto::SignedBigInteger::CompareResult> : Formatter<StringView> {
ErrorOr<void> format(FormatBuilder& builder, Crypto::SignedBigInteger::CompareResult const& compare_result)
{
switch (compare_result) {
case Crypto::SignedBigInteger::CompareResult::DoubleEqualsBigInt:
return builder.put_string("Equals"sv);
case Crypto::SignedBigInteger::CompareResult::DoubleLessThanBigInt:
return builder.put_string("LessThan"sv);
case Crypto::SignedBigInteger::CompareResult::DoubleGreaterThanBigInt:
return builder.put_string("GreaterThan"sv);
default:
return builder.put_string("???"sv);
}
}
};
}