From 505cc3d0c2fc960fb0c39abbf99662f268e26cbf Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@meta.com>
Date: Sun, 3 Aug 2025 08:44:25 -0700
Subject: [PATCH] Simplify remove_trailing_zeros

---
 include/fmt/format-inl.h | 17 +++++++----------
 include/fmt/format.h     |  2 +-
 2 files changed, 8 insertions(+), 11 deletions(-)

diff --git a/include/fmt/format-inl.h b/include/fmt/format-inl.h
index 43596a0f..f49d3beb 100644
--- a/include/fmt/format-inl.h
+++ b/include/fmt/format-inl.h
@@ -1149,7 +1149,7 @@ auto is_left_endpoint_integer_shorter_interval(int exponent) noexcept -> bool {
          exponent <= case_shorter_interval_left_endpoint_upper_threshold;
 }
 
-// Remove trailing zeros from n and return the number of zeros removed (float)
+// Remove trailing zeros from n and return the number of zeros removed (float).
 FMT_INLINE int remove_trailing_zeros(uint32_t& n, int s = 0) noexcept {
   FMT_ASSERT(n != 0, "");
   // Modular inverse of 5 (mod 2^32): (mod_inv_5 * 5) mod 2^32 = 1.
@@ -1170,22 +1170,19 @@ FMT_INLINE int remove_trailing_zeros(uint32_t& n, int s = 0) noexcept {
   return s;
 }
 
-// Removes trailing zeros and returns the number of zeros removed (double)
+// Removes trailing zeros and returns the number of zeros removed (double).
 FMT_INLINE int remove_trailing_zeros(uint64_t& n) noexcept {
   FMT_ASSERT(n != 0, "");
 
-  // This magic number is ceil(2^90 / 10^8).
-  constexpr uint64_t magic_number = 12379400392853802749ull;
-  auto nm = umul128(n, magic_number);
-
   // Is n is divisible by 10^8?
-  if ((nm.high() & ((1ull << (90 - 64)) - 1)) == 0 && nm.low() < magic_number) {
+  constexpr uint32_t ten_pow_8 = 100000000u;
+  if ((n % ten_pow_8) == 0) {
     // If yes, work with the quotient...
-    auto n32 = static_cast<uint32_t>(nm.high() >> (90 - 64));
+    auto n32 = static_cast<uint32_t>(n / ten_pow_8);
     // ... and use the 32 bit variant of the function
-    int s = remove_trailing_zeros(n32, 8);
+    int num_zeros = remove_trailing_zeros(n32, 8);
     n = n32;
-    return s;
+    return num_zeros;
   }
 
   // If n is not divisible by 10^8, work with n itself.
diff --git a/include/fmt/format.h b/include/fmt/format.h
index 11c491ff..43cf7f54 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -1339,7 +1339,7 @@ template <typename WChar, typename Buffer = memory_buffer> class to_utf8 {
 };
 
 // Computes 128-bit result of multiplication of two 64-bit unsigned integers.
-inline auto umul128(uint64_t x, uint64_t y) noexcept -> uint128_fallback {
+FMT_INLINE auto umul128(uint64_t x, uint64_t y) noexcept -> uint128_fallback {
 #if FMT_USE_INT128
   auto p = static_cast<uint128_opt>(x) * static_cast<uint128_opt>(y);
   return {static_cast<uint64_t>(p >> 64), static_cast<uint64_t>(p)};