binius_hal/common.rs
1// Copyright 2025 Irreducible Inc.
2
3use binius_field::{
4 underlier::{UnderlierType, WithUnderlier},
5 PackedField,
6};
7
8// A kibibyte per multilinear seems like a reasonable compromise.
9pub const MAX_SRC_SUBCUBE_LOG_BITS: usize = 13;
10
11// A heuristic to determine the optimal subcube size for sumcheck calc / fold stages.
12//
13// Rough idea is as follows: we want subcubes small enough to create parallelization
14// opportunities, while big enough to amortize dynamic dispatch and leverage L1 caches.
15//
16// Top to bottom, heuristics are:
17// - keep working set at constant bit size ...
18// - accounting for pre-switchover rounds reading from a larger working set (inner_product_vars)
19// - try to minimize wasted effort (max_subcube_src_vars)
20// - do not allow subcubes to be smaller than packing width (P::LOG_WIDTH) ...
21// - unless the multilinear is smaller than a single packed field (max_total_vars)
22pub fn subcube_vars_for_bits<P: PackedField>(
23 max_subcube_src_bits: usize,
24 max_subcube_src_vars: usize,
25 inner_product_vars: usize,
26 max_total_vars: usize,
27) -> usize {
28 let scalar_log_bits = <P::Scalar as WithUnderlier>::Underlier::LOG_BITS;
29 let src_vars = max_subcube_src_vars.min(max_subcube_src_bits - scalar_log_bits);
30
31 src_vars
32 .saturating_sub(inner_product_vars)
33 .max(P::LOG_WIDTH)
34 .min(max_total_vars)
35}