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Simplify remove_trailing_zeros

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This commit is contained in:
Victor Zverovich
2025-08-03 08:44:25 -07:00
parent b8a502615d
commit 505cc3d0c2
2 changed files with 8 additions and 11 deletions
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17
include/fmt/format-inl.h
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@@ -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.

2
include/fmt/format.h
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@@ -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)};