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Improve ISO week-base-year formatter

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Vladislav Shchapov 2021-10-10 19:52:02 +05:00 committed by Victor Zverovich
parent fbaaa5906b
commit 79c00ad8f2
2 changed files with 68 additions and 6 deletions
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36
include/fmt/chrono.h
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@ -1425,10 +1425,37 @@ template <typename FormatContext, typename OutputIt> struct tm_formatter {
}
return {q, r};
}
// Algorithm:
// https://en.wikipedia.org/wiki/ISO_week_date#Calculating_the_week_number_from_a_month_and_day_of_the_month_or_ordinal_date
struct iso_weak {
int year;
int woy;
};
auto tm_iso_year_weaks(int year) -> int {
int p = (year + year / 4 - year / 100 + year / 400) % daysperweek;
int year_1 = year - 1;
int p_1 = (year_1 + year_1 / 4 - year_1 / 100 + year_1 / 400) % daysperweek;
return 52 + ((p == 4 || p_1 == 3) ? 1 : 0);
}
auto tm_iso_weak() -> iso_weak {
auto year = tm_year();
int w = (tm.tm_yday + 10 - (tm.tm_wday == 0 ? daysperweek : tm.tm_wday)) /
daysperweek;
if (w < 1) {
return {year - 1, tm_iso_year_weaks(year - 1)};
} else if (w > tm_iso_year_weaks(year)) {
return {year + 1, 1};
} else {
return {year, w};
}
}
auto tm_hour12() const -> decltype(tm.tm_hour) {
auto hour = tm.tm_hour % 12;
return hour == 0 ? 12 : hour;
}
void write1(size_t value) { *out++ = detail::digits2(value)[1]; }
void write2(size_t value) {
out = std::copy_n(detail::digits2(value), 2, out);
@ -1575,19 +1602,16 @@ template <typename FormatContext, typename OutputIt> struct tm_formatter {
}
void on_iso_week_of_year(numeric_system ns) {
if (ns == numeric_system::standard) {
// TODO: Optimization
format_localized('V');
write2(detail::to_unsigned(tm_iso_weak().woy));
} else {
format_localized('V', 'O');
}
}
void on_iso_week_based_year() {
// TODO: Optimization
format_localized('G');
out = detail::write<char_type>(out, tm_iso_weak().year);
}
void on_iso_week_based_year_last2() {
// TODO: Optimization
format_localized('g');
write2(detail::to_unsigned(tm_split_year(tm_iso_weak().year).lower));
}
void on_day_of_year() {
auto yday = tm.tm_yday + 1;

38
test/chrono-test.cc
View File

@ -7,6 +7,8 @@
#include "fmt/chrono.h"
#include <time.h>
#include <vector>
#include "gtest-extra.h" // EXPECT_THROW_MSG
@ -57,6 +59,42 @@ TEST(chrono_test, format_tm) {
EXPECT_EQ(fmt::format("{:%D}", tm), "04/25/16");
EXPECT_EQ(fmt::format("{:%F}", tm), "2016-04-25");
EXPECT_EQ(fmt::format("{:%T}", tm), "11:22:33");
// for week on the year
// https://www.cl.cam.ac.uk/~mgk25/iso-time.html
std::vector<std::string> str_tm_list = {
"1975-12-29", // W01
"1977-01-02", // W53
"1999-12-27", // W52
"1999-12-31", // W52
"2000-01-01", // W52
"2000-01-02", // W52
"2000-01-03", // W1
};
std::vector<std::string> spec_list = {"%G", "%g", "%V"};
for (const auto& str_tm : str_tm_list) {
tm = std::tm();
// GCC 4 does not support std::get_time
// MSVC dows not support POSIX strptime
#ifdef _WIN32
std::istringstream ss(str_tm);
ss >> std::get_time(&tm, "%Y-%m-%d");
#else
strptime(str_tm.c_str(), "%Y-%m-%d", &tm);
#endif
// Because std::get_time doesn't calculate tm_yday, tm_wday, etc.
tm.tm_isdst = 0;
auto t = std::mktime(&tm);
tm = *std::localtime(&t);
for (const auto& spec : spec_list) {
char output[256] = {};
std::strftime(output, sizeof(output), spec.c_str(), &tm);
auto fmt_spec = std::string("{:").append(spec).append("}");
EXPECT_EQ(output, fmt::format(fmt::runtime(fmt_spec), tm));
}
}
}
// MSVC: