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Optimize grisu_gen_digits

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This commit is contained in:
Victor Zverovich 2020-01-07 16:11:18 -10:00
parent 0201c8db21
commit cef1e4354b
1 changed files with 16 additions and 3 deletions
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19
include/fmt/format-inl.h
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@ -757,6 +757,20 @@ enum result {
};
}
// A version of count_digits optimized for grisu_gen_digits.
inline unsigned grisu_count_digits(uint32_t n) {
if (n < 10) return 1;
if (n < 100) return 2;
if (n < 1000) return 3;
if (n < 10000) return 4;
if (n < 100000) return 5;
if (n < 1000000) return 6;
if (n < 10000000) return 7;
if (n < 100000000) return 8;
if (n < 1000000000) return 9;
return 10;
}
// Generates output using the Grisu digit-gen algorithm.
// error: the size of the region (lower, upper) outside of which numbers
// definitely do not round to value (Delta in Grisu3).
@ -772,7 +786,7 @@ FMT_ALWAYS_INLINE digits::result grisu_gen_digits(fp value, uint64_t error,
FMT_ASSERT(integral == value.f >> -one.e, "");
// The fractional part of scaled value (p2 in Grisu) c = value % one.
uint64_t fractional = value.f & (one.f - 1);
exp = count_digits(integral); // kappa in Grisu.
exp = grisu_count_digits(integral); // kappa in Grisu.
// Divide by 10 to prevent overflow.
auto result = handler.on_start(data::powers_of_10_64[exp - 1] << -one.e,
value.f / 10, error * 10, exp);
@ -1366,8 +1380,7 @@ FMT_FUNC void vprint(std::FILE* f, string_view format_str, format_args args) {
FMT_FUNC void internal::vprint_mojibake(std::FILE* f, string_view format_str,
format_args args) {
memory_buffer buffer;
vformat_to(buffer, format_str,
basic_format_args<buffer_context<char>>(args));
vformat_to(buffer, format_str, basic_format_args<buffer_context<char>>(args));
fwrite_fully(buffer.data(), 1, buffer.size(), f);
}
#endif