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Basics of formatting at compile-time based on compile-time API (#2019)

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Alexey Ochapov 2020-11-29 19:59:11 +03:00 committed by GitHub
parent 119f7dc3d6
commit dac753b81e
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GPG Key ID: 4AEE18F83AFDEB23
4 changed files with 137 additions and 34 deletions
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18
include/fmt/compile.h
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@ -394,7 +394,7 @@ template <typename Char> struct text {
using char_type = Char;
template <typename OutputIt, typename... Args>
OutputIt format(OutputIt out, const Args&...) const {
constexpr OutputIt format(OutputIt out, const Args&...) const {
return write<Char>(out, data);
}
};
@ -413,7 +413,7 @@ template <typename Char> struct code_unit {
using char_type = Char;
template <typename OutputIt, typename... Args>
OutputIt format(OutputIt out, const Args&...) const {
constexpr OutputIt format(OutputIt out, const Args&...) const {
return write<Char>(out, value);
}
};
@ -426,7 +426,7 @@ template <typename Char, typename T, int N> struct field {
using char_type = Char;
template <typename OutputIt, typename... Args>
OutputIt format(OutputIt out, const Args&... args) const {
constexpr OutputIt format(OutputIt out, const Args&... args) const {
// This ensures that the argument type is convertile to `const T&`.
const T& arg = get<N>(args...);
return write<Char>(out, arg);
@ -461,7 +461,7 @@ template <typename L, typename R> struct concat {
using char_type = typename L::char_type;
template <typename OutputIt, typename... Args>
OutputIt format(OutputIt out, const Args&... args) const {
constexpr OutputIt format(OutputIt out, const Args&... args) const {
out = lhs.format(out, args...);
return rhs.format(out, args...);
}
@ -617,8 +617,8 @@ FMT_INLINE std::basic_string<Char> format(const CompiledFormat& cf,
template <typename OutputIt, typename CompiledFormat, typename... Args,
FMT_ENABLE_IF(detail::is_compiled_format<CompiledFormat>::value)>
OutputIt format_to(OutputIt out, const CompiledFormat& cf,
const Args&... args) {
constexpr OutputIt format_to(OutputIt out, const CompiledFormat& cf,
const Args&... args) {
return cf.format(out, args...);
}
# endif // __cpp_if_constexpr
@ -654,8 +654,8 @@ FMT_INLINE std::basic_string<typename S::char_type> format(const S&,
template <typename OutputIt, typename CompiledFormat, typename... Args,
FMT_ENABLE_IF(std::is_base_of<detail::basic_compiled_format,
CompiledFormat>::value)>
OutputIt format_to(OutputIt out, const CompiledFormat& cf,
const Args&... args) {
constexpr OutputIt format_to(OutputIt out, const CompiledFormat& cf,
const Args&... args) {
using char_type = typename CompiledFormat::char_type;
using context = format_context_t<OutputIt, char_type>;
return detail::cf::vformat_to<context>(out, cf,
@ -664,7 +664,7 @@ OutputIt format_to(OutputIt out, const CompiledFormat& cf,
template <typename OutputIt, typename S, typename... Args,
FMT_ENABLE_IF(detail::is_compiled_string<S>::value)>
OutputIt format_to(OutputIt out, const S&, const Args&... args) {
FMT_CONSTEXPR OutputIt format_to(OutputIt out, const S&, const Args&... args) {
constexpr auto compiled = detail::compile<Args...>(S());
return format_to(out, compiled, args...);
}

14
include/fmt/core.h
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@ -96,6 +96,12 @@
# define FMT_CONSTEXPR_DECL
#endif
#if __cplusplus >= 202002L
# define FMT_CONSTEXPR20 constexpr
#else
# define FMT_CONSTEXPR20 inline
#endif
#ifndef FMT_OVERRIDE
# if FMT_HAS_FEATURE(cxx_override_control) || \
(FMT_GCC_VERSION >= 408 && FMT_HAS_GXX_CXX11) || FMT_MSC_VER >= 1900
@ -283,6 +289,14 @@ struct monostate {};
namespace detail {
constexpr bool is_constant_evaluated() FMT_DETECTED_NOEXCEPT {
#ifdef __cpp_lib_is_constant_evaluated
return std::is_constant_evaluated();
#else
return false;
#endif
}
// A helper function to suppress "conditional expression is constant" warnings.
template <typename T> constexpr T const_check(T value) { return value; }

70
include/fmt/format.h
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@ -390,7 +390,7 @@ inline buffer_appender<T> reserve(buffer_appender<T> it, size_t n) {
return it;
}
template <typename Iterator> inline Iterator& reserve(Iterator& it, size_t) {
template <typename Iterator> constexpr Iterator& reserve(Iterator& it, size_t) {
return it;
}
@ -414,7 +414,7 @@ inline std::back_insert_iterator<Container> base_iterator(
}
template <typename Iterator>
inline Iterator base_iterator(Iterator, Iterator it) {
constexpr Iterator base_iterator(Iterator, Iterator it) {
return it;
}
@ -587,14 +587,17 @@ using needs_conversion = bool_constant<
template <typename OutChar, typename InputIt, typename OutputIt,
FMT_ENABLE_IF(!needs_conversion<InputIt, OutChar>::value)>
OutputIt copy_str(InputIt begin, InputIt end, OutputIt it) {
FMT_CONSTEXPR OutputIt copy_str(InputIt begin, InputIt end, OutputIt it) {
while (begin != end) *it++ = *begin++;
return it;
}
template <typename OutChar, typename InputIt,
FMT_ENABLE_IF(!needs_conversion<InputIt, OutChar>::value)>
inline OutChar* copy_str(InputIt begin, InputIt end, OutChar* out) {
FMT_CONSTEXPR20 OutChar* copy_str(InputIt begin, InputIt end, OutChar* out) {
if (is_constant_evaluated()) {
return copy_str<OutChar, InputIt, OutChar*>(begin, end, out);
}
return std::uninitialized_copy(begin, end, out);
}
@ -951,17 +954,7 @@ FMT_EXTERN template struct basic_data<void>;
// This is a struct rather than an alias to avoid shadowing warnings in gcc.
struct data : basic_data<> {};
#ifdef FMT_BUILTIN_CLZLL
// Returns the number of decimal digits in n. Leading zeros are not counted
// except for n == 0 in which case count_digits returns 1.
inline int count_digits(uint64_t n) {
// https://github.com/fmtlib/format-benchmark/blob/master/digits10
auto t = bsr2log10(FMT_BUILTIN_CLZLL(n | 1) ^ 63);
return t - (n < data::zero_or_powers_of_10_64_new[t]);
}
#else
// Fallback version of count_digits used when __builtin_clz is not available.
inline int count_digits(uint64_t n) {
template <typename T> FMT_CONSTEXPR int count_digits_fallback(T n) {
int count = 1;
for (;;) {
// Integer division is slow so do it for a group of four digits instead
@ -975,10 +968,25 @@ inline int count_digits(uint64_t n) {
count += 4;
}
}
#ifdef FMT_BUILTIN_CLZLL
// Returns the number of decimal digits in n. Leading zeros are not counted
// except for n == 0 in which case count_digits returns 1.
FMT_CONSTEXPR20 int count_digits(uint64_t n) {
if (is_constant_evaluated()) {
return count_digits_fallback(n);
}
// https://github.com/fmtlib/format-benchmark/blob/master/digits10
auto t = bsr2log10(FMT_BUILTIN_CLZLL(n | 1) ^ 63);
return t - (n < data::zero_or_powers_of_10_64_new[t]);
}
#else
// Fallback version of count_digits used when __builtin_clz is not available.
FMT_CONSTEXPR int count_digits(uint64_t n) { return count_digits_fallback(n); }
#endif
#if FMT_USE_INT128
inline int count_digits(uint128_t n) {
FMT_CONSTEXPR int count_digits(uint128_t n) {
int count = 1;
for (;;) {
// Integer division is slow so do it for a group of four digits instead
@ -995,7 +1003,7 @@ inline int count_digits(uint128_t n) {
#endif
// Counts the number of digits in n. BITS = log2(radix).
template <unsigned BITS, typename UInt> inline int count_digits(UInt n) {
template <unsigned BITS, typename UInt> FMT_CONSTEXPR int count_digits(UInt n) {
int num_digits = 0;
do {
++num_digits;
@ -1015,7 +1023,10 @@ template <> int count_digits<4>(detail::fallback_uintptr n);
#ifdef FMT_BUILTIN_CLZ
// Optional version of count_digits for better performance on 32-bit platforms.
inline int count_digits(uint32_t n) {
FMT_CONSTEXPR20 int count_digits(uint32_t n) {
if (is_constant_evaluated()) {
return count_digits_fallback(n);
}
auto t = bsr2log10(FMT_BUILTIN_CLZ(n | 1) ^ 31);
return t - (n < data::zero_or_powers_of_10_32_new[t]);
}
@ -1075,11 +1086,20 @@ template <typename Iterator> struct format_decimal_result {
// buffer of specified size. The caller must ensure that the buffer is large
// enough.
template <typename Char, typename UInt>
inline format_decimal_result<Char*> format_decimal(Char* out, UInt value,
int size) {
FMT_CONSTEXPR20 format_decimal_result<Char*> format_decimal(Char* out,
UInt value,
int size) {
FMT_ASSERT(size >= count_digits(value), "invalid digit count");
out += size;
Char* end = out;
if (is_constant_evaluated()) {
while (value >= 10) {
*--out = static_cast<Char>('0' + value % 10);
value /= 10;
}
*--out = static_cast<Char>('0' + value);
return {out, end};
}
while (value >= 100) {
// Integer division is slow so do it for a group of two digits instead
// of for every digit. The idea comes from the talk by Alexandrescu
@ -2048,7 +2068,7 @@ OutputIt write(OutputIt out, string_view value) {
}
template <typename Char, typename OutputIt>
OutputIt write(OutputIt out, basic_string_view<Char> value) {
FMT_CONSTEXPR OutputIt write(OutputIt out, basic_string_view<Char> value) {
auto it = reserve(out, value.size());
it = copy_str<Char>(value.begin(), value.end(), it);
return base_iterator(out, it);
@ -2058,7 +2078,7 @@ template <typename Char, typename OutputIt, typename T,
FMT_ENABLE_IF(is_integral<T>::value &&
!std::is_same<T, bool>::value &&
!std::is_same<T, Char>::value)>
OutputIt write(OutputIt out, T value) {
FMT_CONSTEXPR OutputIt write(OutputIt out, T value) {
auto abs_value = static_cast<uint32_or_64_or_128_t<T>>(value);
bool negative = is_negative(value);
// Don't do -abs_value since it trips unsigned-integer-overflow sanitizer.
@ -2077,19 +2097,19 @@ OutputIt write(OutputIt out, T value) {
}
template <typename Char, typename OutputIt>
OutputIt write(OutputIt out, bool value) {
constexpr OutputIt write(OutputIt out, bool value) {
return write<Char>(out, string_view(value ? "true" : "false"));
}
template <typename Char, typename OutputIt>
OutputIt write(OutputIt out, Char value) {
FMT_CONSTEXPR OutputIt write(OutputIt out, Char value) {
auto it = reserve(out, 1);
*it++ = value;
return base_iterator(out, it);
}
template <typename Char, typename OutputIt>
OutputIt write(OutputIt out, const Char* value) {
FMT_CONSTEXPR OutputIt write(OutputIt out, const Char* value) {
if (!value) {
FMT_THROW(format_error("string pointer is null"));
} else {

69
test/compile-test.cc
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@ -7,6 +7,9 @@
#include <string>
#include <type_traits>
#if __cplusplus >= 202002L
# include <string_view>
#endif
// Check that fmt/compile.h compiles with windows.h included before it.
#ifdef _WIN32
@ -171,3 +174,69 @@ TEST(CompileTest, TextAndArg) {
EXPECT_EQ("42!", fmt::format(FMT_COMPILE("{}!"), 42));
}
#endif
#if __cplusplus >= 202002L
template <size_t max_string_length> struct test_string {
template <typename T> constexpr bool operator==(const T& rhs) const noexcept {
return (std::string_view(rhs).compare(buffer.data()) == 0);
}
std::array<char, max_string_length> buffer{};
};
template <size_t max_string_length, typename... Args>
consteval auto test_format(auto format, const Args&... args) {
test_string<max_string_length> string{};
fmt::format_to(string.buffer.data(), format, args...);
return string;
}
TEST(CompileTimeFormattingTest, Bool) {
{
constexpr auto result = test_format<5>(FMT_COMPILE("{}"), true);
EXPECT_EQ(result, "true");
}
{
constexpr auto result = test_format<6>(FMT_COMPILE("{}"), false);
EXPECT_EQ(result, "false");
}
}
TEST(CompileTimeFormattingTest, Integer) {
{
constexpr auto result = test_format<3>(FMT_COMPILE("{}"), 42);
EXPECT_EQ(result, "42");
}
{
constexpr auto result = test_format<4>(FMT_COMPILE("{}"), 420);
EXPECT_EQ(result, "420");
}
{
constexpr auto result = test_format<6>(FMT_COMPILE("{} {}"), 42, 42);
EXPECT_EQ(result, "42 42");
}
{
constexpr auto result =
test_format<6>(FMT_COMPILE("{} {}"), uint32_t{42}, uint64_t{42});
EXPECT_EQ(result, "42 42");
}
}
TEST(CompileTimeFormattingTest, String) {
{
constexpr auto result = test_format<3>(FMT_COMPILE("{}"), "42");
EXPECT_EQ(result, "42");
}
{
constexpr auto result =
test_format<17>(FMT_COMPILE("{} is {}"), "The answer", "42");
EXPECT_EQ(result, "The answer is 42");
}
}
TEST(CompileTimeFormattingTest, Combination) {
constexpr auto result =
test_format<18>(FMT_COMPILE("{}, {}, {}"), 420, true, "answer");
EXPECT_EQ(result, "420, true, answer");
}
#endif