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accumulator: Change to multiple rotating field elm #53

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Merged
rustaceanrob merged 1 commit into from
Nov 11, 2025
Merged

accumulator: Change to multiple rotating field elm #53

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34 changes: 7 additions & 27 deletions accumulator/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -54,15 +54,14 @@ impl Accumulator {
// ref: https://github.com/rust-bitcoin/rust-bitcoin/blob/7bbb9085c63dc69e9da16ec9c11c698d6236c95c/bitcoin/src/pow.rs#L658
pub fn add(&mut self, outpoint: OutPoint) {
let hash = hash_outpoint(outpoint);
let (big, little) = Self::create_rhs(hash);
let (high, low) = Self::add_internal(self.high, self.low, big, little);
*self = Self { high, low };
self.add_hashed_outpoint(hash);
}

/// Add a pre-hashed outpoint to the accumulator.
pub fn add_hashed_outpoint(&mut self, hash: [u8; 32]) {
let (big, little) = Self::create_rhs(hash);
let (high, low) = Self::add_internal(self.high, self.low, big, little);
let high = self.high.wrapping_add(big);
let low = self.low.wrapping_add(little);
*self = Self { high, low };
}

Expand All @@ -77,36 +76,17 @@ impl Accumulator {
/// Spend the inputs in a block by subtracing them from the accumulator.
pub fn spend(&mut self, outpoint: OutPoint) {
let hash = hash_outpoint(outpoint);
let (high, low) = Self::create_rhs(hash);
let high_inv = !high;
let low_inv = !low;
let (high, low) = Self::add_internal(self.high, self.low, high_inv, low_inv);
let (high, low) = Self::add_internal(high, low, 0, 1);
*self = Self { high, low }
self.spend_hashed_outpoint(hash);
}

/// Spend a pre-hashed outpoint from the accumulator.
pub fn spend_hashed_outpoint(&mut self, hash: [u8; 32]) {
let (high, low) = Self::create_rhs(hash);
let high_inv = !high;
let low_inv = !low;
let (high, low) = Self::add_internal(self.high, self.low, high_inv, low_inv);
let (high, low) = Self::add_internal(high, low, 0, 1);
let (big, little) = Self::create_rhs(hash);
let high = self.high.wrapping_sub(big);
let low = self.low.wrapping_sub(little);
*self = Self { high, low }
}

// Add LHS to RHS, wrapping around if necessary
fn add_internal(lhs_high: u128, lhs_low: u128, rhs_high: u128, rhs_low: u128) -> (u128, u128) {
let high = lhs_high.wrapping_add(rhs_high);
let mut ret_high = high;
let (low, low_bits_overflow) = lhs_low.overflowing_add(rhs_low);
if low_bits_overflow {
// Carry
ret_high = ret_high.wrapping_add(1);
}
(ret_high, low)
}

fn create_rhs(hash: [u8; 32]) -> (u128, u128) {
let (high, low) = split_in_half(hash);
let big = u128::from_be_bytes(high);
Expand Down