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Fix overflow in tm formatter #2564

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merged 1 commit into from
Oct 27, 2021
Merged

Fix overflow in tm formatter #2564

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150 changes: 92 additions & 58 deletions include/fmt/chrono.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1406,79 +1406,110 @@ template <typename OutputIt, typename Char> class tm_writer {
OutputIt out_;
const std::tm& tm_;

auto tm_year() const noexcept -> int { return 1900 + tm_.tm_year; }
auto tm_sec() const noexcept -> int {
FMT_ASSERT(tm_.tm_sec >= 0 && tm_.tm_sec <= 61, "");
return tm_.tm_sec;
}
auto tm_min() const noexcept -> int {
FMT_ASSERT(tm_.tm_min >= 0 && tm_.tm_min <= 59, "");
return tm_.tm_min;
}
auto tm_hour() const noexcept -> int {
FMT_ASSERT(tm_.tm_hour >= 0 && tm_.tm_hour <= 23, "");
return tm_.tm_hour;
}
auto tm_mday() const noexcept -> int {
FMT_ASSERT(tm_.tm_mday >= 1 && tm_.tm_mday <= 31, "");
return tm_.tm_mday;
}
auto tm_mon() const noexcept -> int {
FMT_ASSERT(tm_.tm_mon >= 0 && tm_.tm_mon <= 11, "");
return tm_.tm_mon;
}
auto tm_year() const noexcept -> long long { return 1900ll + tm_.tm_year; }
auto tm_wday() const noexcept -> int {
FMT_ASSERT(tm_.tm_wday >= 0 && tm_.tm_wday <= 6, "");
return tm_.tm_wday;
}
auto tm_yday() const noexcept -> int {
FMT_ASSERT(tm_.tm_yday >= 0 && tm_.tm_yday <= 365, "");
return tm_.tm_yday;
}

auto tm_hour12() const noexcept -> int {
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I suggest merging this function into on_12_hour since it's not used anywhere else.

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The function tm_hour12 will be used in on_12_hour_time. PR #2550 (https://github.com/fmtlib/fmt/pull/2550/files#diff-5d08eff445a9a7793fbd22d873b2284f0ae69f1550aff06f673de49768bccca0R1744-R1750)

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OK, let's keep it then.

auto hour = tm_hour() % 12;
return hour == 0 ? 12 : hour;
}

// POSIX and the C Standard are unclear or inconsistent about what %C and %y
// do if the year is negative or exceeds 9999. Use the convention that %C
// concatenated with %y yields the same output as %Y, and that %Y contains at
// least 4 characters, with more only if necessary.
auto split_year_lower(int year) const noexcept -> int {
auto split_year_lower(long long year) const noexcept -> int {
auto l = year % 100;
if (l < 0) l = -l; // l in [0, 99]
return l;
return static_cast<int>(l);
}

// Algorithm:
// https://en.wikipedia.org/wiki/ISO_week_date#Calculating_the_week_number_from_a_month_and_day_of_the_month_or_ordinal_date
auto iso_year_weeks(const int year) const noexcept -> int {
const long long curr_year = year;
const long long prev_year = curr_year - 1;
const int curr_p = static_cast<int>(
auto iso_year_weeks(long long curr_year) const noexcept -> int {
const auto prev_year = curr_year - 1;
const auto curr_p =
(curr_year + curr_year / 4 - curr_year / 100 + curr_year / 400) %
days_per_week);
const int prev_p = static_cast<int>(
days_per_week;
const auto prev_p =
(prev_year + prev_year / 4 - prev_year / 100 + prev_year / 400) %
days_per_week);
days_per_week;
return 52 + ((curr_p == 4 || prev_p == 3) ? 1 : 0);
}
auto iso_week_num(int tm_yday, int tm_wday) const noexcept -> int {
return (tm_yday + 11 - (tm_wday == 0 ? days_per_week : tm_wday)) /
days_per_week;
}
auto tm_iso_week_year() const noexcept -> int {
auto tm_iso_week_year() const noexcept -> long long {
const auto year = tm_year();
const int w = iso_week_num(tm_.tm_yday, tm_.tm_wday);
const auto w = iso_week_num(tm_yday(), tm_wday());
if (w < 1) return year - 1;
if (w > iso_year_weeks(year)) return year + 1;
return year;
}
auto tm_iso_week_of_year() const noexcept -> int {
const auto year = tm_year();
const int w = iso_week_num(tm_.tm_yday, tm_.tm_wday);
const auto w = iso_week_num(tm_yday(), tm_wday());
if (w < 1) return iso_year_weeks(year - 1);
if (w > iso_year_weeks(year)) return 1;
return w;
}

auto tm_hour12() const noexcept -> int {
auto hour = tm_.tm_hour % 12;
return hour == 0 ? 12 : hour;
void write1(int value) {
*out_++ = static_cast<char>('0' + to_unsigned(value) % 10);
}

void write1(int value) { *out_++ = static_cast<char>('0' + value % 10); }
void write2(int value) {
const char* d = digits2(to_unsigned(value));
const char* d = digits2(to_unsigned(value) % 100);
*out_++ = *d++;
*out_++ = *d;
}

void write_year(int year) {
void write_year_extended(long long year) {
// At least 4 characters.
int width = 4;
if (year < 0) {
*out_++ = '-';
year = 0 - year;
--width;
}
uint32_or_64_or_128_t<long long> n = to_unsigned(year);
const int num_digits = count_digits(n);
if (width > num_digits) out_ = std::fill_n(out_, width - num_digits, '0');
out_ = format_decimal<Char>(out_, n, num_digits).end;
}
void write_year(long long year) {
if (year >= 0 && year < 10000) {
write2(year / 100);
write2(year % 100);
write2(static_cast<int>(year / 100));
write2(static_cast<int>(year % 100));
} else {
// At least 4 characters.
int width = 4;
if (year < 0) {
*out_++ = '-';
year = 0 - year;
--width;
}
uint32_or_64_or_128_t<int> n =
to_unsigned(to_nonnegative_int(year, max_value<int>()));
const int num_digits = count_digits(n);
if (width > num_digits) out_ = std::fill_n(out_, width - num_digits, '0');
out_ = format_decimal<Char>(out_, n, num_digits).end;
write_year_extended(year);
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}
}

Expand Down Expand Up @@ -1522,11 +1553,12 @@ template <typename OutputIt, typename Char> class tm_writer {
void on_full_weekday() { format_localized('A'); }
void on_dec0_weekday(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('w', 'O');
write1(tm_.tm_wday);
write1(tm_wday());
}
void on_dec1_weekday(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('u', 'O');
write1(tm_.tm_wday == 0 ? days_per_week : tm_.tm_wday);
auto wday = tm_wday();
write1(wday == 0 ? days_per_week : wday);
}

void on_abbr_month() { format_localized('b'); }
Expand All @@ -1543,8 +1575,8 @@ template <typename OutputIt, typename Char> class tm_writer {
}
void on_us_date() {
char buf[8];
write_digit2_separated(buf, to_unsigned(tm_.tm_mon + 1),
to_unsigned(tm_.tm_mday),
write_digit2_separated(buf, to_unsigned(tm_mon() + 1),
to_unsigned(tm_mday()),
to_unsigned(split_year_lower(tm_year())), '/');
out_ = copy_str<Char>(std::begin(buf), std::end(buf), out_);
}
Expand All @@ -1556,11 +1588,12 @@ template <typename OutputIt, typename Char> class tm_writer {
copy2(buf, digits2(to_unsigned(year / 100)));
} else {
offset = 4;
write_year(year);
write_year_extended(year);
year = 0;
}
write_digit2_separated(buf + 2, year % 100, to_unsigned(tm_.tm_mon + 1),
to_unsigned(tm_.tm_mday), '-');
write_digit2_separated(buf + 2, static_cast<unsigned>(year % 100),
to_unsigned(tm_mon() + 1), to_unsigned(tm_mday()),
'-');
out_ = copy_str<Char>(std::begin(buf) + offset, std::end(buf), out_);
}

Expand All @@ -1586,25 +1619,26 @@ template <typename OutputIt, typename Char> class tm_writer {
*out_++ = '-';
*out_++ = '0';
} else if (upper >= 0 && upper < 100) {
write2(upper);
write2(static_cast<int>(upper));
} else {
out_ = write<Char>(out_, upper);
}
}

void on_dec_month(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('m', 'O');
write2(tm_.tm_mon + 1);
write2(tm_mon() + 1);
}

void on_dec0_week_of_year(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('U', 'O');
write2((tm_.tm_yday + days_per_week - tm_.tm_wday) / days_per_week);
write2((tm_yday() + days_per_week - tm_wday()) / days_per_week);
}
void on_dec1_week_of_year(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('W', 'O');
write2((tm_.tm_yday + days_per_week -
(tm_.tm_wday == 0 ? (days_per_week - 1) : (tm_.tm_wday - 1))) /
auto wday = tm_wday();
write2((tm_yday() + days_per_week -
(wday == 0 ? (days_per_week - 1) : (wday - 1))) /
days_per_week);
}
void on_iso_week_of_year(numeric_system ns) {
Expand All @@ -1618,49 +1652,49 @@ template <typename OutputIt, typename Char> class tm_writer {
}

void on_day_of_year() {
auto yday = tm_.tm_yday + 1;
auto yday = tm_yday() + 1;
write1(yday / 100);
write2(yday % 100);
}
void on_day_of_month(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('d', 'O');
write2(tm_.tm_mday);
write2(tm_mday());
}
void on_day_of_month_space(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('e', 'O');
const char* d2 = digits2(to_unsigned(tm_.tm_mday));
*out_++ = tm_.tm_mday < 10 ? ' ' : d2[0];
auto mday = to_unsigned(tm_mday()) % 100;
const char* d2 = digits2(mday);
*out_++ = mday < 10 ? ' ' : d2[0];
*out_++ = d2[1];
}

void on_24_hour(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('H', 'O');
write2(tm_.tm_hour);
write2(tm_hour());
}
void on_12_hour(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('I', 'O');
write2(tm_hour12());
}
void on_minute(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('M', 'O');
write2(tm_.tm_min);
write2(tm_min());
}
void on_second(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('S', 'O');
write2(tm_.tm_sec);
write2(tm_sec());
}

void on_12_hour_time() { format_localized('r'); }
void on_24_hour_time() {
write2(tm_.tm_hour);
write2(tm_hour());
*out_++ = ':';
write2(tm_.tm_min);
write2(tm_min());
}
void on_iso_time() {
char buf[8];
write_digit2_separated(buf, to_unsigned(tm_.tm_hour),
to_unsigned(tm_.tm_min), to_unsigned(tm_.tm_sec),
':');
write_digit2_separated(buf, to_unsigned(tm_hour()), to_unsigned(tm_min()),
to_unsigned(tm_sec()), ':');
out_ = copy_str<Char>(std::begin(buf), std::end(buf), out_);
}

Expand Down
7 changes: 7 additions & 0 deletions test/chrono-test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -93,6 +93,13 @@ TEST(chrono_test, format_tm) {
EXPECT_EQ(fmt::format("{:%Y}", tm), "0027");
EXPECT_EQ(fmt::format("{:%C%y}", tm), "0027");

// Overflow year
tm.tm_year = 2147483647;
EXPECT_EQ(fmt::format("{:%Y}", tm), "2147485547");

tm.tm_year = -2147483648;
EXPECT_EQ(fmt::format("{:%Y}", tm), "-2147481748");

// for week on the year
// https://www.cl.cam.ac.uk/~mgk25/iso-time.html
std::vector<std::tm> tm_list = {
Expand Down