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Implement 128-bit count_digits in terms of count_digits_fallback

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Victor Zverovich
2021-03-10 12:57:46 -08:00
parent d9835737f0
commit 85ba271639
1 changed files with 5 additions and 17 deletions
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22
include/fmt/format.h
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@@ -1016,6 +1016,11 @@ template <typename T> FMT_CONSTEXPR int count_digits_fallback(T n) {
count += 4; count += 4;
} }
} }
#if FMT_USE_INT128
FMT_CONSTEXPR inline int count_digits(uint128_t n) {
return count_digits_fallback(n);
}
#endif
#ifdef FMT_BUILTIN_CLZLL #ifdef FMT_BUILTIN_CLZLL
// Returns the number of decimal digits in n. Leading zeros are not counted // Returns the number of decimal digits in n. Leading zeros are not counted
@@ -1035,23 +1040,6 @@ FMT_CONSTEXPR inline int count_digits(uint64_t n) {
} }
#endif #endif
#if FMT_USE_INT128
FMT_CONSTEXPR inline int count_digits(uint128_t n) {
int count = 1;
for (;;) {
// Integer division is slow so do it for a group of four digits instead
// of for every digit. The idea comes from the talk by Alexandrescu
// "Three Optimization Tips for C++". See speed-test for a comparison.
if (n < 10) return count;
if (n < 100) return count + 1;
if (n < 1000) return count + 2;
if (n < 10000) return count + 3;
n /= 10000U;
count += 4;
}
}
#endif
// Counts the number of digits in n. BITS = log2(radix). // Counts the number of digits in n. BITS = log2(radix).
template <unsigned BITS, typename UInt> FMT_CONSTEXPR int count_digits(UInt n) { template <unsigned BITS, typename UInt> FMT_CONSTEXPR int count_digits(UInt n) {
int num_digits = 0; int num_digits = 0;