Expose in-place decimal integer formatting via FormatDec. Improve performance of CountDigits based on the results from https://github.com/localvoid/cxx-benchmark-count-digits.
This commit is contained in:
Victor Zverovich
parent
d473a79581
commit
6f0387fc22
@ -1422,6 +1422,20 @@ TEST(FormatIntTest, FormatInt) {
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EXPECT_EQ(os.str(), fmt::FormatInt(std::numeric_limits<int64_t>::max()).str());
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}
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TEST(FormatIntTest, FormatDec) {
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char buffer[10];
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char *ptr = buffer;
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fmt::FormatDec(ptr, 42);
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EXPECT_EQ(buffer + 2, ptr);
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*ptr = '\0';
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EXPECT_STREQ("42", buffer);
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ptr = buffer;
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fmt::FormatDec(ptr, -42);
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*ptr = '\0';
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EXPECT_EQ(buffer + 3, ptr);
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EXPECT_STREQ("-42", buffer);
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}
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template <typename T>
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std::string str(const T &value) {
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return fmt::str(fmt::Format("{0}") << value);
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35
format.cc
35
format.cc
@ -116,6 +116,29 @@ const char fmt::internal::DIGITS[] =
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"4041424344454647484950515253545556575859"
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"6061626364656667686970717273747576777879"
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"8081828384858687888990919293949596979899";
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const uint64_t fmt::internal::POWERS_OF_10[] = {
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0,
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10,
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100,
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1000,
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10000,
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100000,
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1000000,
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10000000,
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100000000,
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1000000000,
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10000000000,
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100000000000,
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1000000000000,
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10000000000000,
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100000000000000,
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1000000000000000,
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10000000000000000,
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100000000000000000,
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1000000000000000000,
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10000000000000000000u
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};
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void fmt::internal::ReportUnknownType(char code, const char *type) {
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if (std::isprint(static_cast<unsigned char>(code))) {
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@ -145,8 +168,8 @@ typename fmt::BasicWriter<Char>::CharPtr
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}
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template <typename Char>
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void fmt::BasicWriter<Char>::FormatDecimal(
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CharPtr buffer, uint64_t value, unsigned num_digits) {
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void fmt::internal::FormatDecimal(
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Char *buffer, uint64_t value, unsigned num_digits) {
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--num_digits;
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while (value >= 100) {
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// Integer division is slow so do it for a group of two digits instead
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@ -675,8 +698,8 @@ template fmt::BasicWriter<char>::CharPtr
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fmt::BasicWriter<char>::FillPadding(CharPtr buffer,
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unsigned total_size, std::size_t content_size, wchar_t fill);
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template void fmt::BasicWriter<char>::FormatDecimal(
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CharPtr buffer, uint64_t value, unsigned num_digits);
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template void fmt::internal::FormatDecimal<char>(
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char *buffer, uint64_t value, unsigned num_digits);
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template fmt::BasicWriter<char>::CharPtr
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fmt::BasicWriter<char>::PrepareFilledBuffer(
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@ -707,8 +730,8 @@ template fmt::BasicWriter<wchar_t>::CharPtr
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fmt::BasicWriter<wchar_t>::FillPadding(CharPtr buffer,
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unsigned total_size, std::size_t content_size, wchar_t fill);
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template void fmt::BasicWriter<wchar_t>::FormatDecimal(
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CharPtr buffer, uint64_t value, unsigned num_digits);
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template void fmt::internal::FormatDecimal<wchar_t>(
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wchar_t *buffer, uint64_t value, unsigned num_digits);
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template fmt::BasicWriter<wchar_t>::CharPtr
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fmt::BasicWriter<wchar_t>::PrepareFilledBuffer(
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52
format.h
52
format.h
@ -49,6 +49,7 @@
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// Compatibility with compilers other than clang.
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#ifndef __has_feature
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# define __has_feature(x) 0
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# define __has_builtin(x) 0
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#endif
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#ifndef FMT_USE_INITIALIZER_LIST
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@ -171,8 +172,18 @@ void Array<T, SIZE>::append(const T *begin, const T *end) {
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template <typename Char>
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class CharTraits;
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template <typename Char>
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class BasicCharTraits {
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public:
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#if _SECURE_SCL
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typedef stdext::checked_array_iterator<Char*> CharPtr;
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#else
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typedef Char *CharPtr;
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#endif
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};
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template <>
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class CharTraits<char> {
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class CharTraits<char> : public BasicCharTraits<char> {
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private:
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// Conversion from wchar_t to char is not supported.
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// TODO: rename to ConvertChar
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@ -189,7 +200,7 @@ class CharTraits<char> {
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};
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template <>
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class CharTraits<wchar_t> {
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class CharTraits<wchar_t> : public BasicCharTraits<wchar_t> {
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public:
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typedef const char *UnsupportedStrType;
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@ -233,9 +244,17 @@ struct IsLongDouble<long double> { enum {VALUE = 1}; };
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void ReportUnknownType(char code, const char *type);
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extern const uint64_t POWERS_OF_10[];
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// Returns the number of decimal digits in n. Leading zeros are not counted
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// except for n == 0 in which case CountDigits returns 1.
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inline unsigned CountDigits(uint64_t n) {
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#if FMT_GCC_VERSION >= 400 or __has_builtin(__builtin_clzll)
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// Based on http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog10
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// and the benchmark https://github.com/localvoid/cxx-benchmark-count-digits.
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uint64_t t = (64 - __builtin_clzll(n | 1)) * 1233 >> 12;
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return t - (n < POWERS_OF_10[t]) + 1;
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#else
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unsigned count = 1;
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for (;;) {
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// Integer division is slow so do it for a group of four digits instead
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@ -248,12 +267,16 @@ inline unsigned CountDigits(uint64_t n) {
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n /= 10000u;
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count += 4;
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}
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#endif
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}
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extern const char DIGITS[];
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template <typename Char>
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class FormatterProxy;
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template <typename Char>
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void FormatDecimal(Char *buffer, uint64_t value, unsigned num_digits);
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}
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/**
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@ -581,17 +604,14 @@ class BasicWriter {
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friend class BasicFormatter<Char>;
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typedef typename internal::CharTraits<Char>::CharPtr CharPtr;
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#if _SECURE_SCL
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typedef stdext::checked_array_iterator<Char*> CharPtr;
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static Char *GetBase(CharPtr p) { return p.base(); }
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#else
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typedef Char *CharPtr;
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static Char *GetBase(Char *p) { return p; }
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#endif
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static void FormatDecimal(
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CharPtr buffer, uint64_t value, unsigned num_digits);
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static CharPtr FillPadding(CharPtr buffer,
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unsigned total_size, std::size_t content_size, wchar_t fill);
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@ -812,7 +832,7 @@ void BasicWriter<Char>::FormatInt(T value, const Spec &spec) {
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unsigned num_digits = internal::CountDigits(abs_value);
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CharPtr p =
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PrepareFilledBuffer(size + num_digits, spec, sign) + 1 - num_digits;
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BasicWriter::FormatDecimal(p, abs_value, num_digits);
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internal::FormatDecimal(GetBase(p), abs_value, num_digits);
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break;
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}
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case 'x': case 'X': {
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@ -1316,6 +1336,22 @@ class FormatInt {
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std::size_t size() const { return buffer_ - str_ + BUFFER_SIZE - 1; }
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};
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// Formats a decimal integer value writing into buffer and returns
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// a pointer to the end of the formatted string. This function doesn't
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// write a terminating null character.
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template <typename T>
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inline void FormatDec(char *&buffer, T value) {
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typedef typename internal::IntTraits<T>::UnsignedType UnsignedType;
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UnsignedType abs_value = value;
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if (internal::IntTraits<T>::IsNegative(value)) {
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*buffer++ = '-';
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abs_value = 0 - abs_value;
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}
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unsigned num_digits = internal::CountDigits(abs_value);
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internal::FormatDecimal(buffer, abs_value, num_digits);
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buffer += num_digits;
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}
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/**
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\rst
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Formats a string similarly to Python's `str.format
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