Enum RegisterWriter 

pub(crate) enum RegisterWriter {
    None,
    Mul(RegisterId),
    UMulH(u32),
    SMulH(u32),
    AddSub(RegisterId),
    AddConst,
    Xor(RegisterId),
    XorConst,
    Rotate,
}

Information about the instruction that writes to a register, from the perspective of our particular constraints here

This is conceptually similar to storing the last super::Instruction that wrote to a register, but HashX sometimes needs information for constraints which won’t end up in the final Instruction.

We’ve chosen the encoding to minimize the code size in writer_pair_allowed. Most pairwise comparisons can just be a register equality test.

The instructions here fall into three categories which use their own format for encoding arguments:

• Wide Multiply, extra u32

  UMulH and SMulH use an additional otherwise unused 32-bit value from the Rng when considering writer collisions.

  As far as I can tell this is a bug in the original implementation but we can’t change the behavior without breaking compatibility.

  The collisions are rare enough not to be a worthwhile addition to ASIC-resistance. It seems like this was a vestigial feature left over from immediate value matching features which were removed during the development of HashX, but I can’t be sure.

• Constant source

  Only considers the opcode itself, not the specific immediate value.

• Register source

  Considers the source register, collapses add/subtract into one op.

Variants

None

Register not written yet

Mul(RegisterId)

Register source writer for super::Instruction::Mul

UMulH(u32)

Wide multiply writer for super::Instruction::UMulH

SMulH(u32)

Wide multiply writer for super::Instruction::SMulH

AddSub(RegisterId)

Register source writer for super::Instruction::AddShift and super::Instruction::Sub

AddConst

Constant source writer for super::Instruction::AddConst

Xor(RegisterId)

Register source writer for super::Instruction::Xor

XorConst

Constant source writer for super::Instruction::XorConst

Rotate

Constant source writer for super::Instruction::Rotate

Trait Implementations

impl Clone for RegisterWriter

fn clone(&self) -> RegisterWriter

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for RegisterWriter

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for RegisterWriter

fn default() -> RegisterWriter

Returns the “default value” for a type.

impl PartialEq for RegisterWriter

fn eq(&self, other: &RegisterWriter) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Copy for RegisterWriter

impl Eq for RegisterWriter

impl StructuralPartialEq for RegisterWriter