MySQL  8.0.26
Source Code Documentation
integer_digits.h
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24 
25 #ifndef INTEGER_DIGITS_INCLUDED
26 #define INTEGER_DIGITS_INCLUDED
27 
28 #include <assert.h>
29 #include <algorithm>
30 #include <limits>
31 #include <type_traits>
32 
33 /**
34  @file
35 
36  This file contains utilities for accessing digits of integers, and for
37  converting them to strings.
38 */
39 
40 /**
41  Helper class for #write_two_digits(), which creates a table that maps every
42  integer from 0 to 99 to a two-char sequence that represents its two base 10
43  digits.
44 */
46  public:
47  constexpr TwoDigitWriter() {
48  for (int i = 0; i < 100; ++i) {
49  m_digits[i][0] = '0' + i / 10;
50  m_digits[i][1] = '0' + i % 10;
51  }
52  }
53 
54  char *Write(int value, char *to) const {
55  assert(value >= 0 && value < 100);
56  return std::copy_n(m_digits[value], 2, to);
57  }
58 
59  private:
60  char m_digits[100][2]{};
61 };
62 
63 /**
64  Writes an integer, which is between 0 (inclusive) and 100 (exclusive), to a
65  string in base 10. Always writes two digits, zero-padded if necessary. The
66  string is not zero-terminated.
67 
68  @param value the number to write
69  @param[in,out] to the destination string
70  @return pointer to the character just after the last digit
71 */
72 inline char *write_two_digits(int value, char *to) {
73  static constexpr TwoDigitWriter writer;
74  return writer.Write(value, to);
75 }
76 
77 /**
78  Functor that calculates the number of digits in an unsigned integer using
79  binary search. The code for doing the binary search is generated and unrolled
80  at compile time.
81 
82  @tparam T the unsigned integer type of the input to the functor
83  @tparam MinDigits the minimum number of digits the integer is known to have
84  @tparam MaxDigits the maximum number of digits the integer is known to have
85 */
86 template <typename T, int MinDigits, int MaxDigits, typename = void>
87 struct DigitCounter {
88  static_assert(MinDigits < MaxDigits, "");
90  "The input should be an unsigned integer.");
91 
92  constexpr int operator()(T x) const {
93  constexpr int mid = (MinDigits + MaxDigits) / 2;
94  constexpr T pivot = pow10(mid);
95  if (x < pivot)
97  else
99  }
100 
101  private:
102  static constexpr T pow10(int n) {
103  T x = 1;
104  for (int i = 0; i < n; ++i) x *= 10;
105  return x;
106  }
107 };
108 
109 /**
110  Counts the number of digits for the trivial case where the known minimum
111  number of digits is equal to the known maximum number of digits.
112 */
113 template <typename T, int MinDigits, int MaxDigits>
114 struct DigitCounter<T, MinDigits, MaxDigits,
115  typename std::enable_if<MinDigits == MaxDigits>::type> {
116  constexpr int operator()(T) const { return MinDigits; }
117 };
118 
119 /**
120  Counts the number of base 10 digits in an unsigned integer.
121 
122  @param x the number whose digits to count
123  @return the number of digits in the number
124 */
125 template <typename T>
126 constexpr int count_digits(T x) {
128 }
129 
130 /**
131  Writes an unsigned integer of the specified length to a string. The string is
132  not zero-terminated.
133 
134  @param number the number to write
135  @param digits the number of digits to write (the number is zero-padded if it
136  is shorter)
137  @param[in,out] to the destination string
138  @return pointer to the character just after the last digit
139 */
140 template <typename T>
141 inline char *write_digits(T number, int digits, char *to) {
142  assert(digits >= count_digits(number));
143 
144  // The string is built from the end, starting with the least significant
145  // digits.
146  char *pos = to + digits;
147 
148  // The digits are written in groups of two in order to reduce the number of
149  // the relatively expensive modulo and division by 10 operations. If it has an
150  // odd number of digits, write the leftover digit separately.
151  if (digits % 2 != 0) {
152  *--pos = '0' + number % 10;
153  number /= 10;
154  }
155 
156  while (pos > to) {
157  pos -= 2;
158  write_two_digits(number % 100, pos);
159  number /= 100;
160  }
161 
162  return to + digits;
163 }
164 
165 #endif // INTEGER_DIGITS_INCLUDED
Helper class for write_two_digits(), which creates a table that maps every integer from 0 to 99 to a ...
Definition: integer_digits.h:45
char * Write(int value, char *to) const
Definition: integer_digits.h:54
constexpr TwoDigitWriter()
Definition: integer_digits.h:47
char m_digits[100][2]
Definition: integer_digits.h:60
char * pos
Definition: do_ctype.cc:76
char * write_two_digits(int value, char *to)
Writes an integer, which is between 0 (inclusive) and 100 (exclusive), to a string in base 10.
Definition: integer_digits.h:72
constexpr int count_digits(T x)
Counts the number of base 10 digits in an unsigned integer.
Definition: integer_digits.h:126
char * write_digits(T number, int digits, char *to)
Writes an unsigned integer of the specified length to a string.
Definition: integer_digits.h:141
Definition: varlen_sort.h:183
const string value("\"Value\"")
required string type
Definition: replication_group_member_actions.proto:33
static const char digits[]
Definition: stacktrace.cc:592
Functor that calculates the number of digits in an unsigned integer using binary search.
Definition: integer_digits.h:87
constexpr int operator()(T x) const
Definition: integer_digits.h:92
static constexpr T pow10(int n)
Definition: integer_digits.h:102
int n
Definition: xcom_base.cc:445