Move to util and rename

plonky2/src/gates/base_sum.rs

@@ -3,6 +3,7 @@ use std::ops::Range;
 use plonky2_field::extension::Extendable;
 use plonky2_field::packed::PackedField;
 use plonky2_field::types::{Field, Field64};
+use plonky2_util::log_floor;
 
 use crate::gates::gate::Gate;
 use crate::gates::packed_util::PackedEvaluableBase;
@@ -33,7 +34,7 @@ impl<const B: usize> BaseSumGate<B> {
 
     pub fn new_from_config<F: Field64>(config: &CircuitConfig) -> Self {
         let num_limbs =
-            logarithm(F::ORDER as usize, B).min(config.num_routed_wires - Self::START_LIMBS);
+            log_floor(F::ORDER as usize, B).min(config.num_routed_wires - Self::START_LIMBS);
         Self::new(num_limbs)
     }
 
@@ -193,23 +194,6 @@ impl<F: RichField, const B: usize> SimpleGenerator<F> for BaseSplitGenerator<B>
     }
 }
 
-/// Returns the largest `i` such that `base**i < n`.
-const fn logarithm(n: usize, base: usize) -> usize {
-    assert!(n > 0);
-    assert!(base > 1);
-    let mut i = 0;
-    let mut cur: usize = 1;
-    loop {
-        let (mul, overflow) = cur.overflowing_mul(base);
-        if overflow || mul >= n {
-            return i;
-        } else {
-            i += 1;
-            cur = mul;
-        }
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use anyhow::Result;

util/src/lib.rs

@@ -38,6 +38,23 @@ pub fn log2_strict(n: usize) -> usize {
     res as usize
 }
 
+/// Returns the largest `i` such that `base**i < n`.
+pub const fn log_floor(n: usize, base: usize) -> usize {
+    assert!(n > 0);
+    assert!(base > 1);
+    let mut i = 0;
+    let mut cur: usize = 1;
+    loop {
+        let (mul, overflow) = cur.overflowing_mul(base);
+        if overflow || mul >= n {
+            return i;
+        } else {
+            i += 1;
+            cur = mul;
+        }
+    }
+}
+
 /// Permutes `arr` such that each index is mapped to its reverse in binary.
 pub fn reverse_index_bits<T: Copy>(arr: &[T]) -> Vec<T> {
     let n = arr.len();