fmt_helper.h

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// Copyright(c) 2015-present, Gabi Melman & spdlog contributors.
// Distributed under the MIT License (http://opensource.org/licenses/MIT)
#pragma once
 
#include <chrono>
#include <type_traits>
#include <iterator>
#include <spdlog/fmt/fmt.h>
#include <spdlog/common.h>
 
#ifdef SPDLOG_USE_STD_FORMAT
#    include <charconv>
#    include <limits>
#endif
 
// Some fmt helpers to efficiently format and pad ints and strings
namespace spdlog {
namespace details {
namespace fmt_helper {
 
inline spdlog::string_view_t to_string_view(const memory_buf_t &buf) SPDLOG_NOEXCEPT
{
    return spdlog::string_view_t{buf.data(), buf.size()};
}
 
inline void append_string_view(spdlog::string_view_t view, memory_buf_t &dest)
{
    auto *buf_ptr = view.data();
    dest.append(buf_ptr, buf_ptr + view.size());
}
 
#ifdef SPDLOG_USE_STD_FORMAT
template<typename T>
inline void append_int(T n, memory_buf_t &dest)
{
    // Buffer should be large enough to hold all digits (digits10 + 1) and a sign
    SPDLOG_CONSTEXPR const auto BUF_SIZE = std::numeric_limits<T>::digits10 + 2;
    char buf[BUF_SIZE];
 
    auto [ptr, ec] = std::to_chars(buf, buf + BUF_SIZE, n, 10);
    if (ec == std::errc())
    {
        dest.append(buf, ptr);
    }
    else
    {
        throw_spdlog_ex("Failed to format int", static_cast<int>(ec));
    }
}
#else
template<typename T>
inline void append_int(T n, memory_buf_t &dest)
{
    fmt::format_int i(n);
    dest.append(i.data(), i.data() + i.size());
}
#endif
 
template<typename T>
SPDLOG_CONSTEXPR_FUNC unsigned int count_digits_fallback(T n)
{
    // taken from fmt: https://github.com/fmtlib/fmt/blob/8.0.1/include/fmt/format.h#L899-L912
    unsigned 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;
    }
}
 
template<typename T>
inline unsigned int count_digits(T n)
{
    using count_type = typename std::conditional<(sizeof(T) > sizeof(uint32_t)), uint64_t, uint32_t>::type;
#ifdef SPDLOG_USE_STD_FORMAT
    return count_digits_fallback(static_cast<count_type>(n));
#else
    return static_cast<unsigned int>(fmt::
// fmt 7.0.0 renamed the internal namespace to detail.
// See: https://github.com/fmtlib/fmt/issues/1538
#    if FMT_VERSION < 70000
            internal
#    else
            detail
#    endif
        ::count_digits(static_cast<count_type>(n)));
#endif
}
 
inline void pad2(int n, memory_buf_t &dest)
{
    if (n >= 0 && n < 100) // 0-99
    {
        dest.push_back(static_cast<char>('0' + n / 10));
        dest.push_back(static_cast<char>('0' + n % 10));
    }
    else // unlikely, but just in case, let fmt deal with it
    {
        fmt_lib::format_to(std::back_inserter(dest), "{:02}", n);
    }
}
 
template<typename T>
inline void pad_uint(T n, unsigned int width, memory_buf_t &dest)
{
    static_assert(std::is_unsigned<T>::value, "pad_uint must get unsigned T");
    for (auto digits = count_digits(n); digits < width; digits++)
    {
        dest.push_back('0');
    }
    append_int(n, dest);
}
 
template<typename T>
inline void pad3(T n, memory_buf_t &dest)
{
    static_assert(std::is_unsigned<T>::value, "pad3 must get unsigned T");
    if (n < 1000)
    {
        dest.push_back(static_cast<char>(n / 100 + '0'));
        n = n % 100;
        dest.push_back(static_cast<char>((n / 10) + '0'));
        dest.push_back(static_cast<char>((n % 10) + '0'));
    }
    else
    {
        append_int(n, dest);
    }
}
 
template<typename T>
inline void pad6(T n, memory_buf_t &dest)
{
    pad_uint(n, 6, dest);
}
 
template<typename T>
inline void pad9(T n, memory_buf_t &dest)
{
    pad_uint(n, 9, dest);
}
 
// return fraction of a second of the given time_point.
// e.g.
// fraction<std::milliseconds>(tp) -> will return the millis part of the second
template<typename ToDuration>
inline ToDuration time_fraction(log_clock::time_point tp)
{
    using std::chrono::duration_cast;
    using std::chrono::seconds;
    auto duration = tp.time_since_epoch();
    auto secs = duration_cast<seconds>(duration);
    return duration_cast<ToDuration>(duration) - duration_cast<ToDuration>(secs);
}
 
} // namespace fmt_helper
} // namespace details
} // namespace spdlog