mirror of https://github.com/zcash/halo2.git
arithmetic::best_multiexp refactor buckets
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@ -56,24 +56,58 @@ impl<C: CurveAffine> Bucket<C> {
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}
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}
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fn get_at<F: PrimeField>(segment: usize, c: usize, bytes: &F::Repr) -> usize {
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let skip_bits = segment * c;
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let skip_bytes = skip_bits / 8;
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#[derive(Clone)]
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struct Buckets<C: CurveAffine> {
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c: usize,
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coeffs: Vec<Bucket<C>>,
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}
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if skip_bytes >= 32 {
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return 0;
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impl<C: CurveAffine> Buckets<C> {
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fn new(c: usize) -> Self {
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Self {
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c,
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coeffs: vec![Bucket::None; (1 << c) - 1],
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}
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}
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let mut v = [0; 8];
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for (v, o) in v.iter_mut().zip(bytes.as_ref()[skip_bytes..].iter()) {
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*v = *o;
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fn sum(&mut self, coeffs: &[C::Scalar], bases: &[C], i: usize) -> C::Curve {
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// get segmentation and add coeff to buckets content
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for (coeff, base) in coeffs.iter().zip(bases.iter()) {
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let seg = self.get_at::<C::Scalar>(i, &coeff.to_repr());
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if seg != 0 {
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self.coeffs[seg - 1].add_assign(base);
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}
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}
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// Summation by parts
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// e.g. 3a + 2b + 1c = a +
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// (a) + b +
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// ((a) + b) + c
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let mut acc = C::Curve::identity();
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let mut sum = C::Curve::identity();
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self.coeffs.iter().rev().for_each(|b| {
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sum = b.add(sum);
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acc += sum;
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});
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acc
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}
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let mut tmp = u64::from_le_bytes(v);
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tmp >>= skip_bits - (skip_bytes * 8);
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tmp %= 1 << c;
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fn get_at<F: PrimeField>(&self, segment: usize, bytes: &F::Repr) -> usize {
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let skip_bits = segment * self.c;
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let skip_bytes = skip_bits / 8;
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tmp as usize
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if skip_bytes >= 32 {
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0
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} else {
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let mut v = [0; 8];
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for (v, o) in v.iter_mut().zip(bytes.as_ref()[skip_bytes..].iter()) {
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*v = *o;
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}
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let mut tmp = u64::from_le_bytes(v);
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tmp >>= skip_bits - (skip_bytes * 8);
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(tmp % (1 << self.c)) as usize
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}
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}
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}
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/// Performs a small multi-exponentiation operation.
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@ -116,9 +150,7 @@ pub fn best_multiexp<C: CurveAffine>(coeffs: &[C::Scalar], bases: &[C]) -> C::Cu
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(f64::from(bases.len() as u32)).ln().ceil() as usize
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};
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let mut multi_buckets: Vec<Vec<Bucket<C>>> =
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vec![vec![Bucket::None; (1 << c) - 1]; (256 / c) + 1];
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let mut multi_buckets: Vec<Buckets<C>> = vec![Buckets::new(c); (256 / c) + 1];
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let num_threads = multicore::current_num_threads();
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if coeffs.len() > num_threads {
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multi_buckets
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@ -126,24 +158,7 @@ pub fn best_multiexp<C: CurveAffine>(coeffs: &[C::Scalar], bases: &[C]) -> C::Cu
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.enumerate()
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.rev()
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.map(|(i, buckets)| {
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// get segmentation and add coeff to buckets content
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for (coeff, base) in coeffs.iter().zip(bases.iter()) {
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let seg = get_at::<C::Scalar>(i, c, &coeff.to_repr());
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if seg != 0 {
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buckets[seg - 1].add_assign(base);
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}
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}
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// Summation by parts
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// e.g. 3a + 2b + 1c = a +
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// (a) + b +
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// ((a) + b) + c
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let mut acc = C::Curve::identity();
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let mut sum = C::Curve::identity();
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buckets.iter().rev().for_each(|b| {
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sum = b.add(sum);
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acc += sum;
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});
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let mut acc = buckets.sum(coeffs, bases, i);
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(0..c * i).for_each(|_| acc = acc.double());
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acc
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})
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@ -153,27 +168,7 @@ pub fn best_multiexp<C: CurveAffine>(coeffs: &[C::Scalar], bases: &[C]) -> C::Cu
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.iter_mut()
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.enumerate()
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.rev()
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.map(|(i, buckets)| {
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// get segmentation and add coeff to buckets content
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for (coeff, base) in coeffs.iter().zip(bases.iter()) {
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let seg = get_at::<C::Scalar>(i, c, &coeff.to_repr());
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if seg != 0 {
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buckets[seg - 1].add_assign(base);
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}
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}
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// Summation by parts
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// e.g. 3a + 2b + 1c = a +
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// (a) + b +
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// ((a) + b) + c
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let mut acc = C::Curve::identity();
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let mut sum = C::Curve::identity();
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buckets.iter().rev().for_each(|b| {
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sum = b.add(sum);
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acc += sum;
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});
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acc
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})
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.map(|(i, buckets)| buckets.sum(coeffs, bases, i))
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.fold(C::Curve::identity(), |mut sum, bucket| {
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// restore original evaluation point
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(0..c).for_each(|_| sum = sum.double());
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