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Attempt to clarify with an enum.

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This commit is contained in:
Thomas Harte 2022-03-19 12:27:28 -04:00
parent e5af5b57ad
commit 8adb611edf
1 changed files with 24 additions and 1 deletions
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25
InstructionSets/PowerPC/Instruction.hpp
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@ -164,7 +164,30 @@ struct Instruction {
/// Floating point register destination.
uint32_t frD() const { return (opcode >> 21) & 0x1f; }
/// Branch conditional options.
enum BranchOptions: uint32_t {
// Naming convention:
//
// Dec_ prefix => decrement the CTR;
// condition starting NotZero or Zero => test CTR;
// condition ending Set or Clear => test for condition bit.
//
// Numerical suffixes are present because there's some redundancy
// in encodings.
//
// Note that the encodings themselves may suggest alternative means
// of interpretation than mapping via this enum.
Dec_NotZeroAndClear1 = 0b00000, Dec_NotZeroAndClear2 = 0b00001,
Dec_ZeroAndClear1 = 0b00010, Dec_ZeroAndClear2 = 0b00011,
Clear1 = 0b00100, Clear2 = 0b00101,
Dec_NotZeroAndSet1 = 0b01000, Dec_NotZeroAndSet2 = 0b01001,
Dec_ZeroAndSet1 = 0b01010, Dec_ZeroAndSet2 = 0b01011,
Set1 = 0b01100, Set2 = 0b01101,
Dec_NotZero1 = 0b10000, Dec_NotZero2 = 0b10001,
Dec_Zero1 = 0b10010, Dec_Zero2 = 0b10011,
Always = 0b10100,
};
/// Branch conditional options. Cf. the BranchOptions enum.
uint32_t bo() const { return (opcode >> 21) & 0x1f; }
/// Source condition register bit for branch conditionals.
uint32_t bi() const { return (opcode >> 16) & 0x1f; }