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◆ main openmsx / src / utils / Date.cc
4.4 KiB · C++ · last changed chore(): initial commit 1 month ago source blame history raw
e8555c89 Andy McCall 1 
#include "Date.hh"
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#include <array>
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#include <cassert>
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#include <concepts>
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#include <format>
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#include <string_view>
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namespace openmsx::Date {
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static constexpr std::array<std::string_view, 7> days = {
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	"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
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};
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static constexpr std::array<std::string_view, 12> months = {
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	"Jan", "Feb", "Mar", "Apr", "May", "Jun",
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	"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
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};
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template<bool FIRST, unsigned MUL>
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[[nodiscard]] static constexpr bool parseDigit(unsigned c, std::integral auto& t)
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{
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	c -= '0';
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	if (c > 9) return false;
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	if constexpr (FIRST) {
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		t = c * MUL;
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	} else {
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		t += c * MUL;
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	}
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	return true;
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}
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time_t fromString(std::span<const char, 24> s)
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{
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	struct tm tm{};
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	// skip day
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	// space
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	if (s[3] != ' ') return INVALID_TIME_T;
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	// Parse month
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	switch (s[4]) {
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	case 'J': // Jan Jun Jul
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		switch (s[5]) {
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		case 'a': // Jan
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			if (s[6] != 'n') return INVALID_TIME_T;
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			tm.tm_mon = 0; break;
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		case 'u': // Jun Jul
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			switch (s[6]) {
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			case 'n': tm.tm_mon = 5; break;
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			case 'l': tm.tm_mon = 6; break;
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			default: return INVALID_TIME_T;
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			}
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			break;
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		default: return INVALID_TIME_T;
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		}
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		break;
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	case 'F': // Feb
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		if (s[5] != 'e') return INVALID_TIME_T;
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		if (s[6] != 'b') return INVALID_TIME_T;
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		tm.tm_mon = 1;
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		break;
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	case 'M': // Mar May
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		if (s[5] != 'a') return INVALID_TIME_T;
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		switch (s[6]) {
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		case 'r': tm.tm_mon = 2; break;
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		case 'y': tm.tm_mon = 4; break;
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		default: return INVALID_TIME_T;
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		}
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		break;
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	case 'A': // Apr Aug
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		switch (s[5]) {
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		case 'p': // Apr
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			if (s[6] != 'r') return INVALID_TIME_T;
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			tm.tm_mon = 3; break;
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		case 'u': // Aug
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			if (s[6] != 'g') return INVALID_TIME_T;
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			tm.tm_mon = 7; break;
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		default: return INVALID_TIME_T;
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		}
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		break;
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	case 'S': // Sep
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		if (s[5] != 'e') return INVALID_TIME_T;
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		if (s[6] != 'p') return INVALID_TIME_T;
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		tm.tm_mon = 8;
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		break;
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	case 'O': // Oct
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		if (s[5] != 'c') return INVALID_TIME_T;
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		if (s[6] != 't') return INVALID_TIME_T;
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		tm.tm_mon = 9;
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		break;
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	case 'N': // Nov
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		if (s[5] != 'o') return INVALID_TIME_T;
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		if (s[6] != 'v') return INVALID_TIME_T;
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		tm.tm_mon = 10;
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		break;
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	case 'D': // Dec
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		if (s[5] != 'e') return INVALID_TIME_T;
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		if (s[6] != 'c') return INVALID_TIME_T;
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		tm.tm_mon = 11;
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		break;
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	default: return INVALID_TIME_T;
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	}
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	// space
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	if (s[7] != ' ') return INVALID_TIME_T;
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	// parse mday
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	if (!parseDigit<true, 10>(s[8], tm.tm_mday)) return INVALID_TIME_T;
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	if (!parseDigit<false, 1>(s[9], tm.tm_mday)) return INVALID_TIME_T;
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	if ((tm.tm_mday < 1) || (31 < tm.tm_mday))   return INVALID_TIME_T;
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	// space
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	if (s[10] != ' ') return INVALID_TIME_T;
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	// parse hour
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	if (!parseDigit<true, 10>(s[11], tm.tm_hour)) return INVALID_TIME_T;
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	if (!parseDigit<false, 1>(s[12], tm.tm_hour)) return INVALID_TIME_T;
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	if ((tm.tm_hour < 0) || (23 < tm.tm_hour))   return INVALID_TIME_T;
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	// colon
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	if (s[13] != ':') return INVALID_TIME_T;
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	// parse minute
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	if (!parseDigit<true, 10>(s[14], tm.tm_min)) return INVALID_TIME_T;
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	if (!parseDigit<false, 1>(s[15], tm.tm_min)) return INVALID_TIME_T;
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	if ((tm.tm_min < 0) || (59 < tm.tm_min))    return INVALID_TIME_T;
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	// colon
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	if (s[16] != ':') return INVALID_TIME_T;
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	// parse second
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	if (!parseDigit<true, 10>(s[17], tm.tm_sec)) return INVALID_TIME_T;
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	if (!parseDigit<false, 1>(s[18], tm.tm_sec)) return INVALID_TIME_T;
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	if ((tm.tm_sec < 0) || (59 < tm.tm_sec))    return INVALID_TIME_T;
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	// space
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	if (s[19] != ' ') return INVALID_TIME_T;
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	// parse year
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	if (!parseDigit<true, 1000>(s[20], tm.tm_year)) return INVALID_TIME_T;
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	if (!parseDigit<false, 100>(s[21], tm.tm_year)) return INVALID_TIME_T;
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	if (!parseDigit<false,  10>(s[22], tm.tm_year)) return INVALID_TIME_T;
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	if (!parseDigit<false,   1>(s[23], tm.tm_year)) return INVALID_TIME_T;
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	tm.tm_year -= 1900;
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	if (tm.tm_year < 0) return INVALID_TIME_T;
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	tm.tm_isdst = -1;
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	return mktime(&tm);
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}
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std::string_view toString(time_t time, std::span<char, 24> buffer)
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{
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	time = std::max(time, time_t(0));
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	const struct tm* tm = localtime(&time);
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	[[maybe_unused]] auto result = std::format_to_n(
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		buffer.data(), 24, "{} {} {:02d} {:02d}:{:02d}:{:02d} {:04d}",
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		days[tm->tm_wday], months[tm->tm_mon], tm->tm_mday,
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		tm->tm_hour, tm->tm_min, tm->tm_sec,
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		tm->tm_year + 1900);
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	assert(result.size >= 24); // most likely exactly equal to 24, but could be more for year > 9999
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	return {buffer.data(), 24};
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}
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std::string toString(time_t time)
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{
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	std::array<char, 24> buffer;
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	return std::string(toString(time, buffer));
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}
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} // namespace openmsx::Date