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Simplifying format_decimal() #2498

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merged 2 commits into from
Sep 12, 2021
Merged

Simplifying format_decimal() #2498

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8c5c428
Add copy2() constexpr
Roman-Koshelev Sep 12, 2021
9052207
Removed redundant format_decimal implementation for constexpr context
Roman-Koshelev Sep 12, 2021
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24 changes: 12 additions & 12 deletions include/fmt/format.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1049,11 +1049,19 @@ inline auto equal2(const char* lhs, const char* rhs) -> bool {
}

// Copies two characters from src to dst.
template <typename Char> void copy2(Char* dst, const char* src) {
*dst++ = static_cast<Char>(*src++);
*dst = static_cast<Char>(*src);
template <typename Char>
FMT_CONSTEXPR20 FMT_INLINE void copy2(Char* dst, const char* src) {
if (!is_constant_evaluated() && std::is_same<Char, char>::value) {
memcpy(dst, src, 2);
} else {
// We read both bytes before writing so that the compiler can do it in
// one pair of read/write instructions (even if Char aliases char)
char dc0 = *src++;
char dc1 = *src;
*dst++ = static_cast<Char>(dc0);
*dst = static_cast<Char>(dc1);
}
}
FMT_INLINE void copy2(char* dst, const char* src) { memcpy(dst, src, 2); }

template <typename Iterator> struct format_decimal_result {
Iterator begin;
Expand All @@ -1069,14 +1077,6 @@ FMT_CONSTEXPR20 auto format_decimal(Char* out, UInt value, int size)
FMT_ASSERT(size >= count_digits(value), "invalid digit count");
out += size;
Char* end = out;
if (is_constant_evaluated()) {
while (value >= 10) {
*--out = static_cast<Char>('0' + value % 10);
value /= 10;
}
*--out = static_cast<Char>('0' + value);
return {out, end};
}
while (value >= 100) {
// Integer division is slow so do it for a group of two digits instead
// of for every digit. The idea comes from the talk by Alexandrescu
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