/// <summary>
/// Constructs an <see cref="InsertCopyLengthCode"/> that can encode the stored lengths, and can therefore be used as context in the <see cref="Serialize"/>.
/// </summary>
public InsertCopyLengthCode MakeCode(ImplicitDistanceCodeZero implicitDCZ)
{
int insertCode = CollectionHelper.FindRangeIndex(InsertCodeRanges, InsertLength);
int copyCode = CollectionHelper.FindRangeIndex(CopyCodeRanges, CopyLength);
return(new InsertCopyLengthCode(insertCode, copyCode, implicitDCZ));
}
public static bool Decide(this ImplicitDistanceCodeZero strategy, int insertCode, int copyCode)
{
return(strategy switch {
ImplicitDistanceCodeZero.Disable
=> false,
ImplicitDistanceCodeZero.PreferEnabled
=> insertCode <= 7 && copyCode <= 15,
ImplicitDistanceCodeZero.ForceEnabled when insertCode > 7
=> throw new ArgumentOutOfRangeException(nameof(insertCode), "Insert code must be in the range [0; 7] when using implied distance code zero."),
ImplicitDistanceCodeZero.ForceEnabled when copyCode > 15
=> throw new ArgumentOutOfRangeException(nameof(copyCode), "Copy code must be in the range [0; 15] when using implied distance code zero."),
ImplicitDistanceCodeZero.ForceEnabled
=> true,
_ => throw new InvalidOperationException("Invalid implicit distance code zero strategy: " + strategy),
});
/// <summary>
/// Initializes the code with the concrete insert and copy codes, and the flag which determines whether to use an implied distance code zero.
/// </summary>
public InsertCopyLengthCode(int insertCode, int copyCode, ImplicitDistanceCodeZero implicitDCZ)
{
if (insertCode < 0 || insertCode > 23)
{
throw new ArgumentOutOfRangeException(nameof(insertCode), "Insert code must be in the range [0; 23].");
}
if (copyCode < 0 || copyCode > 23)
{
throw new ArgumentOutOfRangeException(nameof(copyCode), "Copy code must be in the range [0; 23].");
}
bool useDistanceCodeZero = implicitDCZ.Decide(insertCode, copyCode);
int cell = DetermineCellIndex(insertCode, copyCode, useDistanceCodeZero);
this.CompactedCode = (64 * cell) + ((insertCode & 0b111) << 3) | (copyCode & 0b111);
this.InsertCode = insertCode;
this.CopyCode = copyCode;
this.UseDistanceCodeZero = useDistanceCodeZero;
}
