From db06b0df875856968c562d564b595a4e2861144e Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@meta.com>
Date: Sun, 29 Sep 2024 16:57:29 -0700
Subject: [PATCH] Use countl_zero in bigint

---
 include/fmt/format.h | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/include/fmt/format.h b/include/fmt/format.h
index a2dbdf98..62681924 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -2831,10 +2831,8 @@ class bigint {
   FMT_CONSTEXPR20 void assign_pow10(int exp) {
     FMT_ASSERT(exp >= 0, "");
     if (exp == 0) return *this = 1;
-    // Find the top bit.
-    int bitmask = 1;
-    while (exp >= bitmask) bitmask <<= 1;
-    bitmask >>= 1;
+    int bitmask = 1 << (num_bits<unsigned>() -
+                        countl_zero(static_cast<uint32_t>(exp)) - 1);
     // pow(10, exp) = pow(5, exp) * pow(2, exp). First compute pow(5, exp) by
     // repeated squaring and multiplication.
     *this = 5;