From c32292ba21e778fe1567082eec4032b00c625d9e Mon Sep 17 00:00:00 2001
From: Hannes Karppila <hannes.karppila@gmail.com>
Date: Fri, 27 Jan 2023 14:03:53 +0200
Subject: [PATCH] Use the recently stabilized checked_ilog

---
 .../src/interpreter/executors/instruction.rs  | 45 +------------------
 .../instruction/tests/math_operations.rs      |  8 ++--
 2 files changed, 5 insertions(+), 48 deletions(-)

diff --git a/fuel-vm/src/interpreter/executors/instruction.rs b/fuel-vm/src/interpreter/executors/instruction.rs
index 2147e02dca..2d3efacf06 100644
--- a/fuel-vm/src/interpreter/executors/instruction.rs
+++ b/fuel-vm/src/interpreter/executors/instruction.rs
@@ -132,7 +132,7 @@ where
                 self.gas_charge(self.gas_costs.mlog)?;
                 self.alu_error(
                     ra,
-                    |b, c| checked_ilog(b, c).expect("checked_ilog returned None for valid values") as Word,
+                    |b, c| b.checked_ilog(c).expect("checked_ilog returned None for valid values") as Word,
                     b,
                     c,
                     b == 0 || c <= 1,
@@ -546,48 +546,5 @@ fn checked_nth_root(target: u64, nth_root: u64) -> Option<u64> {
     Some(guess + 1)
 }
 
-/// Computes logarithm for given exponent and base.
-/// Diverges when exp == 0 or base <= 1.
-///
-/// This code is originally from [rust corelib][rust-corelib-impl],
-/// but with all additional clutter removed.
-///
-/// [rust-corelib-impl]: https://github.com/rust-lang/rust/blob/415d8fcc3e17f8c1324a81cf2aa7127b4fcfa32e/library/core/src/num/uint_macros.rs#L774
-#[inline(always)] // Force copy of each invocation for optimization, see comments below
-const fn _unchecked_ilog_inner(exp: Word, base: Word) -> u32 {
-    let mut n = 0;
-    let mut r = exp;
-    while r >= base {
-        r /= base;
-        n += 1;
-    }
-
-    n
-}
-
-/// Logarithm for given exponent and an arbitrary base, rounded
-/// rounded down to nearest integer value.
-///
-/// Returns `None` if the exponent == 0, or if the base <= 1.
-///
-/// TODO: when <https://github.com/rust-lang/rust/issues/70887> is stabilized,
-/// consider using that instead.
-const fn checked_ilog(exp: Word, base: Word) -> Option<u32> {
-    if exp == 0 || base <= 1 {
-        return None;
-    }
-
-    // Generate separately optimized paths for some common and/or expensive bases.
-    // See <https://github.com/FuelLabs/fuel-vm/issues/150#issuecomment-1288797787> for benchmark.
-    Some(match base {
-        2 => _unchecked_ilog_inner(exp, 2),
-        3 => _unchecked_ilog_inner(exp, 3),
-        4 => _unchecked_ilog_inner(exp, 4),
-        5 => _unchecked_ilog_inner(exp, 5),
-        10 => _unchecked_ilog_inner(exp, 10),
-        n => _unchecked_ilog_inner(exp, n),
-    })
-}
-
 #[cfg(test)]
 mod tests;
diff --git a/fuel-vm/src/interpreter/executors/instruction/tests/math_operations.rs b/fuel-vm/src/interpreter/executors/instruction/tests/math_operations.rs
index 7f2e2c7068..083b979da0 100644
--- a/fuel-vm/src/interpreter/executors/instruction/tests/math_operations.rs
+++ b/fuel-vm/src/interpreter/executors/instruction/tests/math_operations.rs
@@ -1,14 +1,14 @@
 use num_integer::Roots;
 use rayon::prelude::*;
 
-use super::{checked_ilog, checked_nth_root};
+use super::checked_nth_root;
 
 /// Check for https://github.com/FuelLabs/fuel-vm/issues/150
 #[test]
 fn mlog_rounding_issues() {
-    assert_eq!(checked_ilog(999, 10), Some(2));
-    assert_eq!(checked_ilog(1000, 10), Some(3));
-    assert_eq!(checked_ilog(1001, 10), Some(3));
+    assert_eq!(999u32.checked_ilog(10), Some(2));
+    assert_eq!(1000u32.checked_ilog(10), Some(3));
+    assert_eq!(1001u32.checked_ilog(10), Some(3));
 }
 
 /// Verify some subsets of possible inputs against a known-good implementation.