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This commit is contained in:
Thomas Harte 2023-10-24 16:43:22 -04:00
parent 26c2a29b99
commit cc9e8117ab
1 changed files with 10 additions and 0 deletions
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InstructionSets/x86/Instruction.hpp
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@ -702,6 +702,16 @@ template<bool is_32bit> class Instruction {
// [b4, b0]: dest.
uint16_t source_data_dest_sib_ = 1 << 10; // So that ::Invalid doesn't seem to have a length extension.
// Note to future self: if source length continues to prove avoidable, reuse its four bits as:
// three bits: segment (as overridden, otherwise whichever operand has a segment, if either);
// one bit: an extra bit for Operation.
//
// Then what was the length extension will hold only a repetition, if any, and the lock bit. As luck would have
// it there are six valid segment registers so there is an available sentinel value to put into the segment
// field to indicate that there's an extension if necessary. A further three bits would need to be trimmed
// to do away with that extension entirely, but since lock is rarely used and repetitions apply only to a
// small number of operations I think it'd at least be a limited problem.
bool has_length_extension() const {
return !((source_data_dest_sib_ >> 10) & 15);
}