GeographicLib: Utility.cpp Source File

GeographicLib 2.5

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Utility.cpp
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1/**
2 * \file Utility.cpp
3 * \brief Implementation for GeographicLib::Utility class
4 *
5 * Copyright (c) Charles Karney (2011-2022) <karney@alum.mit.edu> and licensed
6 * under the MIT/X11 License. For more information, see
7 * https://geographiclib.sourceforge.io/
8 **********************************************************************/
9
10#include <cstdlib>
11#include <GeographicLib/Utility.hpp>
12
13#if defined(_MSC_VER)
14// Squelch warnings about unsafe use of getenv
15# pragma warning (disable: 4996)
16#endif
17
18namespace GeographicLib {
19
20 using namespace std;
21
22 int Utility::day(int y, int m, int d) {
23 // Convert from date to sequential day and vice versa
24 //
25 // Here is some code to convert a date to sequential day and vice
26 // versa. The sequential day is numbered so that January 1, 1 AD is day 1
27 // (a Saturday). So this is offset from the "Julian" day which starts the
28 // numbering with 4713 BC.
29 //
30 // This is inspired by a talk by John Conway at the John von Neumann
31 // National Supercomputer Center when he described his Doomsday algorithm
32 // for figuring the day of the week. The code avoids explicitly doing ifs
33 // (except for the decision of whether to use the Julian or Gregorian
34 // calendar). Instead the equivalent result is achieved using integer
35 // arithmetic. I got this idea from the routine for the day of the week
36 // in MACLisp (I believe that that routine was written by Guy Steele).
37 //
38 // There are three issues to take care of
39 //
40 // 1. the rules for leap years,
41 // 2. the inconvenient placement of leap days at the end of February,
42 // 3. the irregular pattern of month lengths.
43 //
44 // We deal with these as follows:
45 //
46 // 1. Leap years are given by simple rules which are straightforward to
47 // accommodate.
48 //
49 // 2. We simplify the calculations by moving January and February to the
50 // previous year. Here we internally number the months March–December,
51 // January, February as 0–9, 10, 11.
52 //
53 // 3. The pattern of month lengths from March through January is regular
54 // with a 5-month period—31, 30, 31, 30, 31, 31, 30, 31, 30, 31, 31. The
55 // 5-month period is 153 days long. Since February is now at the end of
56 // the year, we don't need to include its length in this part of the
57 // calculation.
58 bool greg = gregorian(y, m, d);
59 y += (m + 9) / 12 - 1; // Move Jan and Feb to previous year,
60 m = (m + 9) % 12; // making March month 0.
61 return
62 (1461 * y) / 4 // Julian years converted to days. Julian year is 365 +
63 // 1/4 = 1461/4 days.
64 // Gregorian leap year corrections. The 2 offset with respect to the
65 // Julian calendar synchronizes the vernal equinox with that at the
66 // time of the Council of Nicea (325 AD).
67 + (greg ? (y / 100) / 4 - (y / 100) + 2 : 0)
68 + (153 * m + 2) / 5 // The zero-based start of the m'th month
69 + d - 1 // The zero-based day
70 - 305; // The number of days between March 1 and December 31.
71 // This makes 0001-01-01 day 1
72 }
73
74 int Utility::day(int y, int m, int d, bool check) {
75 int s = day(y, m, d);
76 if (!check)
77 return s;
78 int y1, m1, d1;
79 date(s, y1, m1, d1);
80 if (!(s > 0 && y == y1 && m == m1 && d == d1))
81 throw GeographicErr("Invalid date " +
82 str(y) + "-" + str(m) + "-" + str(d)
83 + (s > 0 ? "; use " +
84 str(y1) + "-" + str(m1) + "-" + str(d1) :
85 " before 0001-01-01"));
86 return s;
87 }
88
89 void Utility::date(int s, int& y, int& m, int& d) {
90 int c = 0;
91 bool greg = gregorian(s);
92 s += 305; // s = 0 on March 1, 1BC
93 if (greg) {
94 s -= 2; // The 2 day Gregorian offset
95 // Determine century with the Gregorian rules for leap years. The
96 // Gregorian year is 365 + 1/4 - 1/100 + 1/400 = 146097/400 days.
97 c = (4 * s + 3) / 146097;
98 s -= (c * 146097) / 4; // s = 0 at beginning of century
99 }
100 y = (4 * s + 3) / 1461; // Determine the year using Julian rules.
101 s -= (1461 * y) / 4; // s = 0 at start of year, i.e., March 1
102 y += c * 100; // Assemble full year
103 m = (5 * s + 2) / 153; // Determine the month
104 s -= (153 * m + 2) / 5; // s = 0 at beginning of month
105 d = s + 1; // Determine day of month
106 y += (m + 2) / 12; // Move Jan and Feb back to original year
107 m = (m + 2) % 12 + 1; // Renumber the months so January = 1
108 }
109
110 void Utility::date(const std::string& s, int& y, int& m, int& d) {
111 if (s == "now") {
112 time_t t = time(0);
113 struct tm* now = gmtime(&t);
114 y = now->tm_year + 1900;
115 m = now->tm_mon + 1;
116 d = now->tm_mday;
117 return;
118 }
119 int y1, m1 = 1, d1 = 1;
120 const char* digits = "0123456789";
121 string::size_type p1 = s.find_first_not_of(digits);
122 if (p1 == string::npos)
123 y1 = val<int>(s);
124 else if (s[p1] != '-')
125 throw GeographicErr("Delimiter not hyphen in date " + s);
126 else if (p1 == 0)
127 throw GeographicErr("Empty year field in date " + s);
128 else {
129 y1 = val<int>(s.substr(0, p1));
130 if (++p1 == s.size())
131 throw GeographicErr("Empty month field in date " + s);
132 string::size_type p2 = s.find_first_not_of(digits, p1);
133 if (p2 == string::npos)
134 m1 = val<int>(s.substr(p1));
135 else if (s[p2] != '-')
136 throw GeographicErr("Delimiter not hyphen in date " + s);
137 else if (p2 == p1)
138 throw GeographicErr("Empty month field in date " + s);
139 else {
140 m1 = val<int>(s.substr(p1, p2 - p1));
141 if (++p2 == s.size())
142 throw GeographicErr("Empty day field in date " + s);
143 d1 = val<int>(s.substr(p2));
144 }
145 }
146 y = y1; m = m1; d = d1;
147 }
148
149 std::string Utility::trim(const std::string& s) {
150 unsigned
151 beg = 0,
152 end = unsigned(s.size());
153 while (beg < end && isspace(s[beg]))
154 ++beg;
155 while (beg < end && isspace(s[end - 1]))
156 --end;
157 return string(s, beg, end-beg);
158 }
159
160 int Utility::lookup(const std::string& s, char c) {
161 string::size_type r = s.find(char(toupper(c)));
162 return r == string::npos ? -1 : int(r);
163 }
164
165 int Utility::lookup(const char* s, char c) {
166 const char* p = strchr(s, toupper(c));
167 return p != NULL ? int(p - s) : -1;
168 }
169
170 bool Utility::ParseLine(const std::string& line,
171 std::string& key, std::string& value,
172 char equals, char comment) {
173 key.clear(); value.clear();
174 string::size_type n = comment ? line.find(comment) : line.size();
175 string linea = trim(line.substr(0, n));
176 if (linea.empty()) return false;
177 n = equals ? linea.find(equals) : linea.find_first_of(" \t\n\v\f\r");
178 key = trim(linea.substr(0, n));
179 if (key.empty()) return false;
180 if (n != string::npos) value = trim(linea.substr(n + 1));
181 return true;
182 }
183
184 int Utility::set_digits(int ndigits) {
185#if GEOGRAPHICLIB_PRECISION == 5
186 if (ndigits <= 0) {
187 char* digitenv = getenv("GEOGRAPHICLIB_DIGITS");
188 if (digitenv)
189 ndigits = strtol(digitenv, NULL, 0);
190 if (ndigits <= 0)
191 ndigits = 256;
192 }
193#endif
194 return Math::set_digits(ndigits);
195 }
196
197} // namespace GeographicLib
Utility.hpp
Header for GeographicLib::Utility class.
GeographicLib::GeographicErr
Exception handling for GeographicLib.
Definition Constants.hpp:316
GeographicLib::Math::set_digits
static int set_digits(int ndigits)
Definition Math.cpp:29
GeographicLib::Utility::date
static void date(int s, int &y, int &m, int &d)
Definition Utility.cpp:89
GeographicLib::Utility::lookup
static int lookup(const std::string &s, char c)
Definition Utility.cpp:160
GeographicLib::Utility::ParseLine
static bool ParseLine(const std::string &line, std::string &key, std::string &value, char equals='\0', char comment='#')
Definition Utility.cpp:170
GeographicLib::Utility::val
static T val(const std::string &s)
Definition Utility.hpp:225
GeographicLib::Utility::set_digits
static int set_digits(int ndigits=0)
Definition Utility.cpp:184
GeographicLib::Utility::trim
static std::string trim(const std::string &s)
Definition Utility.cpp:149
GeographicLib::Utility::day
static int day(int y, int m=1, int d=1)
Definition Utility.cpp:22
GeographicLib::Utility::str
static std::string str(T x, int p=-1)
Definition Utility.hpp:161
GeographicLib
Namespace for GeographicLib.
Definition Accumulator.cpp:12