diff --git a/soroban-env-host/src/host/metered_map.rs b/soroban-env-host/src/host/metered_map.rs index d3bb13162..22bbcba6d 100644 --- a/soroban-env-host/src/host/metered_map.rs +++ b/soroban-env-host/src/host/metered_map.rs @@ -7,6 +7,8 @@ use crate::{ use std::{borrow::Borrow, cmp::Ordering, marker::PhantomData}; +use super::metered_vector::binary_search_by_pre_rust_182; + const MAP_OOB: Error = Error::from_type_and_code(ScErrorType::Object, ScErrorCode::IndexBounds); pub struct MeteredOrdMap { @@ -161,7 +163,7 @@ where let _span = tracy_span!("map lookup"); self.charge_binsearch(ctx)?; let mut err: Option = None; - let res = self.map.binary_search_by(|probe| { + let res = binary_search_by_pre_rust_182(self.map.as_slice(), |probe| { // We've already hit an error, return Ordering::Equal // to terminate search asap. if err.is_some() { diff --git a/soroban-env-host/src/host/metered_vector.rs b/soroban-env-host/src/host/metered_vector.rs index e492dce7d..29b157182 100644 --- a/soroban-env-host/src/host/metered_vector.rs +++ b/soroban-env-host/src/host/metered_vector.rs @@ -287,7 +287,7 @@ where { self.charge_binsearch(budget)?; let mut err: Option = None; - let res = self.vec.binary_search_by(|probe| { + let res = binary_search_by_pre_rust_182(self.vec.as_slice(), |probe| { // We've already hit an error, return Ordering::Equal // to terminate search asap. if err.is_some() { @@ -373,3 +373,57 @@ where >>::compare(self, &a.vec, &b.vec) } } + +/// This is a copy of implementation of Rust stdlib `binary_search_by` function +/// pre-Rust-1.82 with a minor modifications. +/// +/// We cannot rely on the standard library implementation as it might change and +/// thus change the observed metering as well. Thus we are just using the same +/// hardcoded implementation. +/// +/// The code is copied from the following file revision: +/// https://github.com/rust-lang/rust/blob/8f7af88b33771ab5ec92a2a767a97a068f2ea17b/library/core/src/slice/mod.rs#L2769 +/// Modifications are no-op: switched &self to an explicit `slice` argument, +/// removed assertions and unsafe blocks. +pub(crate) fn binary_search_by_pre_rust_182(slice: &[T], mut f: F) -> Result +where + F: FnMut(&T) -> std::cmp::Ordering, +{ + // INVARIANTS: + // - 0 <= left <= left + size = right <= self.len() + // - f returns Less for everything in self[..left] + // - f returns Greater for everything in self[right..] + let mut size = slice.len(); + let mut left = 0; + let mut right = size; + while left < right { + let mid = left + size / 2; + + // SAFETY: the while condition means `size` is strictly positive, so + // `size/2 < size`. Thus `left + size/2 < left + size`, which + // coupled with the `left + size <= self.len()` invariant means + // we have `left + size/2 < self.len()`, and this is in-bounds. + let cmp = f(slice.get(mid).unwrap()); + + // This control flow produces conditional moves, which results in + // fewer branches and instructions than if/else or matching on + // cmp::Ordering. + // This is x86 asm for u8: https://rust.godbolt.org/z/698eYffTx. + left = if cmp == std::cmp::Ordering::Less { + mid + 1 + } else { + left + }; + right = if cmp == std::cmp::Ordering::Greater { + mid + } else { + right + }; + if cmp == std::cmp::Ordering::Equal { + return Ok(mid); + } + + size = right - left; + } + Err(left) +}