Replace mod_inv_25 by explicit value (#3450)

fmtlib · May 18, 2023 · d60b907 · d60b907
1 parent 4ce086f
commit d60b907
Showing 1 changed file with 4 additions and 7 deletions.
diff --git a/include/fmt/format-inl.h b/include/fmt/format-inl.h
@@ -1131,11 +1131,8 @@ bool is_left_endpoint_integer_shorter_interval(int exponent) noexcept {
 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.
-  // See https://github.com/fmtlib/fmt/issues/3163 for more details.
-  const uint32_t mod_inv_5 = 0xcccccccd;
-  // Casts are needed to workaround a bug in MSVC 19.22 and older.
-  const uint32_t mod_inv_25 =
-      static_cast<uint32_t>(uint64_t(mod_inv_5) * mod_inv_5);
+  constexpr uint32_t mod_inv_5 = 0xcccccccd;
+  constexpr uint32_t mod_inv_25 = 0xc28f5c29; // = mod_inv_5 * mod_inv_5
 
   while (true) {
     auto q = rotr(n * mod_inv_25, 2);
@@ -1170,8 +1167,8 @@ FMT_INLINE int remove_trailing_zeros(uint64_t& n) noexcept {
   }
 
   // If n is not divisible by 10^8, work with n itself.
-  const uint64_t mod_inv_5 = 0xcccccccccccccccd;
-  const uint64_t mod_inv_25 = mod_inv_5 * mod_inv_5;
+  constexpr uint64_t mod_inv_5 = 0xcccccccccccccccd;
+  constexpr uint64_t mod_inv_25 = 0x8f5c28f5c28f5c29; // = mod_inv_5 * mod_inv_5
 
   int s = 0;
   while (true) {