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LibCrypto: Add a method to count the number of digits in a big int

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This commit is contained in:
Timothy Flynn
2026-02-21 08:46:06 -05:00
committed by Tim Flynn
parent 79d5fdc871
commit ecdaa7911f
Notes: github-actions[bot] 2026-02-22 14:40:33 +00:00 
Author: https://github.com/trflynn89
Commit: https://github.com/LadybirdBrowser/ladybird/commit/ecdaa7911f8
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/8063
3 changed files with 41 additions and 0 deletions
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14
Libraries/LibCrypto/BigInt/UnsignedBigInteger.cpp
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@@ -147,6 +147,20 @@ ErrorOr<String> UnsignedBigInteger::to_base(u16 N) const
return StringView(buffer.bytes().slice(0, written - 1)).to_ascii_lowercase_string();
}
size_t UnsignedBigInteger::count_digits_in_base(u16 base) const
{
VERIFY(base <= 36);
if (is_zero())
return 1;
int size = 0;
MP_MUST(mp_radix_size(&m_mp, base, &size));
// mp_radix_size includes a null byte.
return static_cast<size_t>(size) - 1;
}
u64 UnsignedBigInteger::to_u64() const
{
return mp_get_u64(&m_mp);

2
Libraries/LibCrypto/BigInt/UnsignedBigInteger.h
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@@ -47,6 +47,8 @@ public:
[[nodiscard]] static ErrorOr<UnsignedBigInteger> from_base(u16 N, StringView str);
[[nodiscard]] ErrorOr<String> to_base(u16 N) const;
[[nodiscard]] size_t count_digits_in_base(u16 base) const;
[[nodiscard]] u64 to_u64() const;
enum class RoundingMode {

25
Tests/LibCrypto/TestBigInteger.cpp
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@@ -209,6 +209,31 @@ TEST_CASE(test_unsigned_bigint_base10_to_string)
EXPECT_EQ(result, "57195071295721390579057195715793");
}
TEST_CASE(test_unsigned_bigint_count_digits)
{
constexpr auto count_digits = [](u64 number, u16 base) {
u8 digits = 0;
do {
number /= base;
++digits;
} while (number > 0);
return digits;
};
for (auto base : to_array<u16>({ 2, 8, 10, 16 })) {
for (auto test : to_array<u64>({ 0, 9, 10, 19, 99, 100, 999, 1000, 9999, 10000, 99999, 10000000000, 99999999999 })) {
auto bigint = Crypto::UnsignedBigInteger { test };
auto result = bigint.count_digits_in_base(base);
auto expected = count_digits(test, base);
EXPECT_EQ(result, expected);
}
}
}
static size_t count_leading_zeros(Bytes data)
{
auto leading_zeros = 0u;