/// <summary>
/// Inject a compiled sub-unit into this writer
/// References to string constants will be recalculated
/// </summary>
public void Merge(NanCodeWriter fragment)
{
var codes = fragment._opcodes;
var strings = fragment._stringTable;
AddSymbols(fragment._symbols);
foreach (var code in codes)
{
var type = NanTags.TypeOf(code);
switch (type)
{
case DataType.Invalid: throw new Exception("Invalid opcode when merging");
case DataType.ValInt32:
case DataType.ValUInt32:
case DataType.VariableRef:
case DataType.Number:
case DataType.Opcode:
_opcodes.Add(code);
break;
case DataType.PtrString:
case DataType.PtrStaticString:
NanTags.DecodePointer(code, out var target, out _);
LiteralString(strings[(int)target]);
break;
// all other types are only expected at runtime (so far)
default: throw new Exception("Unexpected opcode when merging");
}
}
}
/// <summary>
/// Write opcodes and data section to stream
/// References to string constants will be recalculated
/// </summary>
public void WriteToStream(Stream output)
{
// a string is [NanTag(UInt32): byte length] [string bytes, padded to 8 byte chunks]
// 1) Calculate the string table size
var dataLength = _stringTable.Select(CalculatePaddedSize).Sum() + _stringTable.Count;
// 2) Write a jump command to skip the table
var jumpCode = NanTags.EncodeLongOpcode('c', 's', (uint)dataLength);
WriteCode(output, jumpCode);
// 3) Write the strings, with a mapping dictionary
long location = 1; // counting initial jump as 0
var mapping = new Dictionary <long, long>(); // original index, final memory location
for (var index = 0; index < _stringTable.Count; index++)
{
var staticStr = _stringTable[index];
var bytes = Encoding.ASCII.GetBytes(staticStr);
var chunks = CalculatePaddedSize(staticStr);
var padSize = (chunks * 8) - bytes.Length;
mapping.Add(index, location);
var headerOpCode = NanTags.EncodeUInt32((uint)bytes.Length);
WriteCode(output, headerOpCode);
location++;
output.Write(bytes, 0, bytes.Length);
location += chunks;
for (int p = 0; p < padSize; p++)
{
output.WriteByte(0);
}
}
// 4) Write the op-codes
foreach (var code in _opcodes)
{
var type = NanTags.TypeOf(code);
switch (type)
{
case DataType.PtrString:
case DataType.PtrStaticString:
NanTags.DecodePointer(code, out var original, out _);
var final = mapping[original];
WriteCode(output, NanTags.EncodePointer(final, DataType.PtrStaticString));
break;
default:
WriteCode(output, code);
break;
}
}
output.Flush();
}
