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This commit is contained in:
Thomas Harte 2023-10-26 23:27:56 -04:00
parent 11b032fb06
commit 5b0d2d754f
1 changed files with 4 additions and 13 deletions
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17
InstructionSets/x86/Instruction.hpp
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@ -693,13 +693,11 @@ template<bool is_32bit> class Instruction {
// Packing and encoding of fields is admittedly somewhat convoluted; what this
// achieves is that instructions will be sized:
//
// four bytes + up to three extension words
// (two bytes for 16-bit instructions, four for 32)
// four bytes + up to two extension words
// (extension words being two bytes for 16-bit instructions, four for 32)
//
// Two of the extension words are used to retain an operand and displacement
// if the instruction has those. The other can store sizes greater than 15
// bytes (for earlier processors), plus any repetition, segment override or
// repetition prefixes.
// The extension words are used to retain an operand and displacement
// if the instruction has those.
// b7: address size;
// b6: has displacement;
@ -739,13 +737,6 @@ template<bool is_32bit> class Instruction {
return
offsetof(Instruction<is_32bit>, extensions) +
(has_displacement() + has_operand()) * sizeof(ImmediateT);
// To consider in the future: the length extension is always the last one,
// and uses only 8 bits of content within 32-bit instructions, so it'd be
// possible further to trim the packing size on little endian machines.
//
// ... but is that a speed improvement? How much space does it save, and
// is it enough to undo the costs of unaligned data?
}
private: