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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System.Collections;
using System.Diagnostics;
using System.Security.Cryptography;
namespace System.Formats.Asn1
{
public sealed partial class AsnWriter
{
/// <summary>
/// Write a [<see cref="FlagsAttribute"/>] enum value as a NamedBitList with
/// a specified tag.
/// </summary>
/// <param name="value">The boxed enumeration value to write</param>
/// <param name="tag">The tag to write, or <see langword="null"/> for the default tag (Universal 3).</param>
/// <exception cref="ArgumentException">
/// <paramref name="tag"/>.<see cref="Asn1Tag.TagClass"/> is
/// <see cref="TagClass.Universal"/>, but
/// <paramref name="tag"/>.<see cref="Asn1Tag.TagValue"/> is not correct for
/// the method.
///
/// -or-
///
/// <paramref name="value"/> is not a boxed enum value.
///
/// -or-
///
/// the unboxed type of <paramref name="value"/> is not declared [<see cref="FlagsAttribute"/>].
/// </exception>
/// <exception cref="ArgumentNullException">
/// <paramref name="value"/> is <see langword="null"/>.
/// </exception>
public void WriteNamedBitList(Enum value, Asn1Tag? tag = null)
{
if (value is null)
{
throw new ArgumentNullException(nameof(value));
}
CheckUniversalTag(tag, UniversalTagNumber.BitString);
WriteNamedBitList(tag, value.GetType(), value);
}
/// <summary>
/// Write a [<see cref="FlagsAttribute"/>] enum value as a NamedBitList with
/// a specified tag.
/// </summary>
/// <param name="value">The enumeration value to write</param>
/// <param name="tag">The tag to write, or <see langword="null"/> for the default tag (Universal 3).</param>
/// <exception cref="ArgumentException">
/// <paramref name="tag"/>.<see cref="Asn1Tag.TagClass"/> is
/// <see cref="TagClass.Universal"/>, but
/// <paramref name="tag"/>.<see cref="Asn1Tag.TagValue"/> is not correct for
/// the method.
///
/// -or-
///
/// <typeparamref name="TEnum"/> is not an enum value.
///
/// -or-
///
/// <typeparamref name="TEnum"/> is not declared [<see cref="FlagsAttribute"/>].
/// </exception>
public void WriteNamedBitList<TEnum>(TEnum value, Asn1Tag? tag = null) where TEnum : Enum
{
CheckUniversalTag(tag, UniversalTagNumber.BitString);
WriteNamedBitList(tag, typeof(TEnum), value);
}
/// <summary>
/// Write a bit array value as a NamedBitList with a specified tag.
/// </summary>
/// <param name="value">The bits to write</param>
/// <param name="tag">The tag to write, or <see langword="null"/> for the default tag (Universal 3).</param>
/// <exception cref="ArgumentException">
/// <paramref name="tag"/>.<see cref="Asn1Tag.TagClass"/> is
/// <see cref="TagClass.Universal"/>, but
/// <paramref name="tag"/>.<see cref="Asn1Tag.TagValue"/> is not correct for
/// the method.
/// </exception>
/// <exception cref="ArgumentNullException">
/// <paramref name="value"/> is <see langword="null"/>.
/// </exception>
/// <remarks>
/// The index of the bit array corresponds to the bit number in the encoded format, which is
/// different than the value produced by <see cref="BitArray.CopyTo"/> with a byte array.
/// For example, the bit array <c>{ false, true, true }</c> encodes as <c>0b0110_0000</c> with 5
/// unused bits.
/// </remarks>
public void WriteNamedBitList(BitArray value, Asn1Tag? tag = null)
{
if (value is null)
{
throw new ArgumentNullException(nameof(value));
}
CheckUniversalTag(tag, UniversalTagNumber.BitString);
WriteBitArray(value, tag);
}
private void WriteNamedBitList(Asn1Tag? tag, Type tEnum, Enum value)
{
Type backingType = tEnum.GetEnumUnderlyingType();
if (!tEnum.IsDefined(typeof(FlagsAttribute), false))
{
throw new ArgumentException(
SR.Argument_NamedBitListRequiresFlagsEnum,
nameof(tEnum));
}
ulong integralValue;
if (backingType == typeof(ulong))
{
integralValue = Convert.ToUInt64(value);
}
else
{
// All other types fit in a (signed) long.
long numericValue = Convert.ToInt64(value);
integralValue = unchecked((ulong)numericValue);
}
WriteNamedBitList(tag, integralValue);
}
// T-REC-X.680-201508 sec 22
// T-REC-X.690-201508 sec 8.6, 11.2.2
private void WriteNamedBitList(Asn1Tag? tag, ulong integralValue)
{
Span<byte> temp = stackalloc byte[sizeof(ulong)];
// Reset to all zeros, since we're just going to or-in bits we need.
temp.Clear();
int indexOfHighestSetBit = -1;
for (int i = 0; integralValue != 0; integralValue >>= 1, i++)
{
if ((integralValue & 1) != 0)
{
temp[i / 8] |= (byte)(0x80 >> (i % 8));
indexOfHighestSetBit = i;
}
}
if (indexOfHighestSetBit < 0)
{
// No bits were set; this is an empty bit string.
// T-REC-X.690-201508 sec 11.2.2-note2
WriteBitString(ReadOnlySpan<byte>.Empty, tag: tag);
}
else
{
// At least one bit was set.
// Determine the shortest length necessary to represent the bit string.
// Since "bit 0" gets written down 0 => 1.
// Since "bit 8" is in the second byte 8 => 2.
// That makes the formula ((bit / 8) + 1) instead of ((bit + 7) / 8).
int byteLen = (indexOfHighestSetBit / 8) + 1;
int unusedBitCount = 7 - (indexOfHighestSetBit % 8);
WriteBitString(
temp.Slice(0, byteLen),
unusedBitCount,
tag);
}
}
private void WriteBitArray(BitArray value, Asn1Tag? tag)
{
if (value.Count == 0)
{
// No bits were set; this is an empty bit string.
// T-REC-X.690-201508 sec 11.2.2-note2
WriteBitString(ReadOnlySpan<byte>.Empty, tag: tag);
return;
}
int requiredBytes = checked((value.Count + 7) / 8);
int unusedBits = requiredBytes * 8 - value.Count;
byte[] rented = CryptoPool.Rent(requiredBytes);
// Export the BitArray to a byte array.
// While bits 0-7 are in the first byte, they are numbered 76543210,
// but our wire form is 01234567, so we'll need to reverse the bits on each byte.
value.CopyTo(rented, 0);
Span<byte> valueSpan = rented.AsSpan(0, requiredBytes);
AsnDecoder.ReverseBitsPerByte(valueSpan);
WriteBitString(valueSpan, unusedBits, tag);
CryptoPool.Return(rented, requiredBytes);
}
}
}
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