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Fix formatting of padding #306

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Merged
mborland merged 3 commits into from
Jan 30, 2026
+112 −32
Merged

Fix formatting of padding #306

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b18f324
Add padding failure
mborland Jan 30, 2026
3862036
Fix fmt support and testing
mborland Jan 30, 2026
1a5b81f
Fix <format> support and testing
mborland Jan 30, 2026
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43 changes: 41 additions & 2 deletions include/boost/int128/fmt_format.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -286,10 +286,49 @@ struct formatter
const auto end = detail::mini_to_chars(buffer, abs_v, base, is_upper);
std::string s(end, buffer + sizeof(buffer));

// Calculate prefix length that will be added later
std::size_t prefix_len {0};
if (prefix)
{
switch (base)
{
case 2:
case 16:
prefix_len = 2; // "0b", "0B", "0x", or "0X"
break;
case 8:
prefix_len = 1; // "0"
break;
default:
break;
}
}

// Calculate sign length that will be added later
std::size_t sign_len {0};
if (sign == sign_option::plus || sign == sign_option::space || isneg)
{
sign_len = 1;
}

// Zero-padding only applies when no explicit alignment is set
if (align == alignment::none && s.size() - 1u < static_cast<std::size_t>(padding_digits))
// Account for prefix and sign in the padding calculation
if (align == alignment::none && padding_digits > 0)
{
s.insert(s.begin(), static_cast<std::size_t>(padding_digits) - s.size() + 1u, '0');
auto target_digit_width {static_cast<std::size_t>(padding_digits)};
if (target_digit_width > prefix_len + sign_len)
{
target_digit_width -= prefix_len + sign_len;
}
else
{
target_digit_width = 0;
}

if (s.size() - 1u < target_digit_width)
{
s.insert(s.begin(), target_digit_width - s.size() + 1u, '0');
}
}

if (prefix)
Expand Down
43 changes: 41 additions & 2 deletions include/boost/int128/format.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -274,10 +274,49 @@ struct formatter<T>
const auto end = boost::int128::detail::mini_to_chars(buffer, abs_v, base, is_upper);
std::string s(end, buffer + sizeof(buffer));

// Calculate prefix length that will be added later
std::size_t prefix_len {0};
if (prefix)
{
switch (base)
{
case 2:
case 16:
prefix_len = 2; // "0b", "0B", "0x", or "0X"
break;
case 8:
prefix_len = 1; // "0"
break;
default:
break;
}
}

// Calculate sign length that will be added later
std::size_t sign_len {0};
if (sign == boost::int128::detail::sign_option::plus || sign == boost::int128::detail::sign_option::space || isneg)
{
sign_len = 1;
}

// Zero-padding only applies when no explicit alignment is set
if (align == boost::int128::detail::alignment::none && s.size() - 1u < static_cast<std::size_t>(padding_digits))
// Account for prefix and sign in the padding calculation
if (align == boost::int128::detail::alignment::none && padding_digits > 0)
{
s.insert(s.begin(), static_cast<std::size_t>(padding_digits) - s.size() + 1u, '0');
auto target_digit_width {static_cast<std::size_t>(padding_digits)};
if (target_digit_width > prefix_len + sign_len)
{
target_digit_width -= prefix_len + sign_len;
}
else
{
target_digit_width = 0;
}

if (s.size() - 1u < target_digit_width)
{
s.insert(s.begin(), target_digit_width - s.size() + 1u, '0');
}
}

if (prefix)
Expand Down
30 changes: 16 additions & 14 deletions test/test_fmt_format.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -48,8 +48,10 @@ void test_binary()
BOOST_TEST_CSTR_EQ(fmt::format("{:#B}", T{5}).c_str(), "0B101");

BOOST_TEST_CSTR_EQ(fmt::format("{:6b}", T{5}).c_str(), "000101");
BOOST_TEST_CSTR_EQ(fmt::format("{:#6b}", T{5}).c_str(), "0b000101");
BOOST_TEST_CSTR_EQ(fmt::format("{:#06B}", T{5}).c_str(), "0B000101");
BOOST_TEST_CSTR_EQ(fmt::format("{:#6b}", T{5}).c_str(), "0b0101");
BOOST_TEST_CSTR_EQ(fmt::format("{:#06B}", T{5}).c_str(), "0B0101");

BOOST_TEST_CSTR_EQ(fmt::format("{:#010b}", T{42}).c_str(), "0b00101010");
}

template <typename T>
Expand All @@ -59,7 +61,7 @@ void test_octal()
BOOST_TEST_CSTR_EQ(fmt::format("{:#o}", T{42}).c_str(), "052");

BOOST_TEST_CSTR_EQ(fmt::format("{:4o}", T{42}).c_str(), "0052");
BOOST_TEST_CSTR_EQ(fmt::format("{:#4o}", T{42}).c_str(), "00052");
BOOST_TEST_CSTR_EQ(fmt::format("{:#4o}", T{42}).c_str(), "0052");
}

template <typename T>
Expand All @@ -74,8 +76,8 @@ void test_decimal()
BOOST_TEST_CSTR_EQ(fmt::format("{: d}", T{42}).c_str(), " 42");
BOOST_TEST_CSTR_EQ(fmt::format("{: #d}", T{42}).c_str(), " 42");

BOOST_TEST_CSTR_EQ(fmt::format("{:+3d}", T{42}).c_str(), "+042");
BOOST_TEST_CSTR_EQ(fmt::format("{:+#3d}", T{42}).c_str(), "+042");
BOOST_TEST_CSTR_EQ(fmt::format("{:+3d}", T{42}).c_str(), "+42");
BOOST_TEST_CSTR_EQ(fmt::format("{:+#3d}", T{42}).c_str(), "+42");

BOOST_TEST_CSTR_EQ(fmt::format("{:-3d}", T{42}).c_str(), "042");
BOOST_TEST_CSTR_EQ(fmt::format("{:-#3d}", T{42}).c_str(), "042");
Expand All @@ -84,14 +86,14 @@ void test_decimal()
template <typename T>
void test_decimal_negative()
{
BOOST_TEST_CSTR_EQ(fmt::format("{: 3d}", T{42}).c_str(), " 042");
BOOST_TEST_CSTR_EQ(fmt::format("{: #3d}", T{42}).c_str(), " 042");
BOOST_TEST_CSTR_EQ(fmt::format("{: 3d}", T{42}).c_str(), " 42");
BOOST_TEST_CSTR_EQ(fmt::format("{: #3d}", T{42}).c_str(), " 42");

BOOST_TEST_CSTR_EQ(fmt::format("{:-3d}", T{-42}).c_str(), "-042");
BOOST_TEST_CSTR_EQ(fmt::format("{:-#3d}", T{-42}).c_str(), "-042");
BOOST_TEST_CSTR_EQ(fmt::format("{:-3d}", T{-42}).c_str(), "-42");
BOOST_TEST_CSTR_EQ(fmt::format("{:-#3d}", T{-42}).c_str(), "-42");

BOOST_TEST_CSTR_EQ(fmt::format("{: 3d}", T{-42}).c_str(), "-042");
BOOST_TEST_CSTR_EQ(fmt::format("{: #3d}", T{-42}).c_str(), "-042");
BOOST_TEST_CSTR_EQ(fmt::format("{: 3d}", T{-42}).c_str(), "-42");
BOOST_TEST_CSTR_EQ(fmt::format("{: #3d}", T{-42}).c_str(), "-42");
}

template <typename T>
Expand All @@ -110,10 +112,10 @@ void test_hex()
BOOST_TEST_CSTR_EQ(fmt::format("{:+#X}", T{42}).c_str(), "+0X2A");

BOOST_TEST_CSTR_EQ(fmt::format("{:5X}", T{42}).c_str(), "0002A");
BOOST_TEST_CSTR_EQ(fmt::format("{:#5X}", T{42}).c_str(), "0X0002A");
BOOST_TEST_CSTR_EQ(fmt::format("{:#5X}", T{42}).c_str(), "0X02A");

BOOST_TEST_CSTR_EQ(fmt::format("{: 5X}", T{42}).c_str(), " 0002A");
BOOST_TEST_CSTR_EQ(fmt::format("{: #5X}", T{42}).c_str(), " 0X0002A");
BOOST_TEST_CSTR_EQ(fmt::format("{: 5X}", T{42}).c_str(), " 002A");
BOOST_TEST_CSTR_EQ(fmt::format("{: #5X}", T{42}).c_str(), " 0X2A");
}

template <typename T>
Expand Down
28 changes: 14 additions & 14 deletions test/test_format.cpp
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -41,8 +41,8 @@ void test_binary()
BOOST_TEST_CSTR_EQ(std::format("{:#B}", T{5}).c_str(), "0B101");

BOOST_TEST_CSTR_EQ(std::format("{:6b}", T{5}).c_str(), "000101");
BOOST_TEST_CSTR_EQ(std::format("{:#6b}", T{5}).c_str(), "0b000101");
BOOST_TEST_CSTR_EQ(std::format("{:#06B}", T{5}).c_str(), "0B000101");
BOOST_TEST_CSTR_EQ(std::format("{:#6b}", T{5}).c_str(), "0b0101");
BOOST_TEST_CSTR_EQ(std::format("{:#06B}", T{5}).c_str(), "0B0101");
}

template <typename T>
Expand All @@ -52,7 +52,7 @@ void test_octal()
BOOST_TEST_CSTR_EQ(std::format("{:#o}", T{42}).c_str(), "052");

BOOST_TEST_CSTR_EQ(std::format("{:4o}", T{42}).c_str(), "0052");
BOOST_TEST_CSTR_EQ(std::format("{:#4o}", T{42}).c_str(), "00052");
BOOST_TEST_CSTR_EQ(std::format("{:#4o}", T{42}).c_str(), "0052");
}

template <typename T>
Expand All @@ -67,22 +67,22 @@ void test_decimal()
BOOST_TEST_CSTR_EQ(std::format("{: d}", T{42}).c_str(), " 42");
BOOST_TEST_CSTR_EQ(std::format("{: #d}", T{42}).c_str(), " 42");

BOOST_TEST_CSTR_EQ(std::format("{:+3d}", T{42}).c_str(), "+042");
BOOST_TEST_CSTR_EQ(std::format("{:+#3d}", T{42}).c_str(), "+042");
BOOST_TEST_CSTR_EQ(std::format("{:+3d}", T{42}).c_str(), "+42");
BOOST_TEST_CSTR_EQ(std::format("{:+#3d}", T{42}).c_str(), "+42");

BOOST_TEST_CSTR_EQ(std::format("{:-3d}", T{42}).c_str(), "042");
BOOST_TEST_CSTR_EQ(std::format("{:-#3d}", T{42}).c_str(), "042");

if constexpr (std::is_same_v<T, boost::int128::int128_t>)
{
BOOST_TEST_CSTR_EQ(std::format("{: 3d}", T{42}).c_str(), " 042");
BOOST_TEST_CSTR_EQ(std::format("{: #3d}", T{42}).c_str(), " 042");
BOOST_TEST_CSTR_EQ(std::format("{: 3d}", T{42}).c_str(), " 42");
BOOST_TEST_CSTR_EQ(std::format("{: #3d}", T{42}).c_str(), " 42");

BOOST_TEST_CSTR_EQ(std::format("{:-3d}", T{-42}).c_str(), "-042");
BOOST_TEST_CSTR_EQ(std::format("{:-#3d}", T{-42}).c_str(), "-042");
BOOST_TEST_CSTR_EQ(std::format("{:-3d}", T{-42}).c_str(), "-42");
BOOST_TEST_CSTR_EQ(std::format("{:-#3d}", T{-42}).c_str(), "-42");

BOOST_TEST_CSTR_EQ(std::format("{: 3d}", T{-42}).c_str(), "-042");
BOOST_TEST_CSTR_EQ(std::format("{: #3d}", T{-42}).c_str(), "-042");
BOOST_TEST_CSTR_EQ(std::format("{: 3d}", T{-42}).c_str(), "-42");
BOOST_TEST_CSTR_EQ(std::format("{: #3d}", T{-42}).c_str(), "-42");
}

BOOST_TEST_CSTR_EQ(std::format("{:+d}", T{42}).c_str(), "+42");
Expand Down Expand Up @@ -112,10 +112,10 @@ void test_hex()
}

BOOST_TEST_CSTR_EQ(std::format("{:5X}", T{42}).c_str(), "0002A");
BOOST_TEST_CSTR_EQ(std::format("{:#5X}", T{42}).c_str(), "0X0002A");
BOOST_TEST_CSTR_EQ(std::format("{:#5X}", T{42}).c_str(), "0X02A");

BOOST_TEST_CSTR_EQ(std::format("{: 5X}", T{42}).c_str(), " 0002A");
BOOST_TEST_CSTR_EQ(std::format("{: #5X}", T{42}).c_str(), " 0X0002A");
BOOST_TEST_CSTR_EQ(std::format("{: 5X}", T{42}).c_str(), " 002A");
BOOST_TEST_CSTR_EQ(std::format("{: #5X}", T{42}).c_str(), " 0X2A");
}

template <typename T>
Expand Down