lib/main/google/olc/olc_private.h

   1 /*
   2  * We place these static definitions on a separate header file so that we can
   3  * include the file in both the library and the tests.
   4  */
   5
   6 #include <ctype.h>
   7 #include <float.h>
   8 #include <math.h>
   9 #include <memory.h>
  10
  11 #define OLC_kEncodingBase 20
  12 #define OLC_kGridCols 4
  13 #define OLC_kLatMaxDegrees 90
  14 #define OLC_kLonMaxDegrees 180
  15
  16 // Separates the first eight digits from the rest of the code.
  17 static const char kSeparator = '+';
  18 // Used to indicate null values before the separator.
  19 static const char kPaddingCharacter = '0';
  20 // Digits used in the codes.
  21 static const char kAlphabet[] = "23456789CFGHJMPQRVWX";
  22 // Number of digits in the alphabet.
  23 static const size_t kEncodingBase = OLC_kEncodingBase;
  24 // The max number of digits returned in a plus code. Roughly 1 x 0.5 cm.
  25 static const size_t kMaximumDigitCount = 15;
  26 // The number of code characters that are lat/lng pairs.
  27 static const size_t kPairCodeLength = 10;
  28 // The number of characters that combine lat and lng into a grid.
  29 // kMaximumDigitCount - kPairCodeLength
  30 static const size_t kGridCodeLength = 5;
  31 // The number of columns in each grid step.
  32 static const size_t kGridCols = OLC_kGridCols;
  33 // The number of rows in each grid step.
  34 static const size_t kGridRows = OLC_kEncodingBase / OLC_kGridCols;
  35 // The number of digits before the separator.
  36 static const size_t kSeparatorPosition = 8;
  37 // Inverse of the precision of the last pair digits (in degrees).
  38 static const size_t kPairPrecisionInverse = 8000;
  39 // Inverse (1/) of the precision of the final grid digits in degrees.
  40 // Latitude is kEncodingBase^3 * kGridRows^kGridCodeLength
  41 static const size_t kGridLatPrecisionInverse = 2.5e7;
  42 // Longitude is kEncodingBase^3 * kGridColumns^kGridCodeLength
  43 static const size_t kGridLonPrecisionInverse = 8.192e6;
  44 // Latitude bounds are -kLatMaxDegrees degrees and +kLatMaxDegrees degrees
  45 // which we transpose to 0 and 180 degrees.
  46 static const double kLatMaxDegrees = OLC_kLatMaxDegrees;
  47 static const double kLatMaxDegreesT2 = 2 * OLC_kLatMaxDegrees;
  48
  49 // Longitude bounds are -kLonMaxDegrees degrees and +kLonMaxDegrees degrees
  50 // which we transpose to 0 and 360 degrees.
  51 static const double kLonMaxDegrees = OLC_kLonMaxDegrees;
  52 static const double kLonMaxDegreesT2 = 2 * OLC_kLonMaxDegrees;
  53
  54 // Lookup table of the alphabet positions of characters 'C' through 'X',
  55 // inclusive. A value of -1 means the character isn't part of the alphabet.
  56 static const int kPositionLUT['X' - 'C' + 1] = {
  57     8,  -1, -1, 9,  10, 11, -1, 12, -1, -1, 13,
  58     -1, -1, 14, 15, 16, -1, -1, -1, 17, 18, 19,
  59 };
  60
  61 // Returns the position of a char in the encoding alphabet, or -1 if invalid.
  62 static int get_alphabet_position(char c) {
  63   char uc = toupper(c);
  64   // We use a lookup table for performance reasons.
  65   if (uc >= 'C' && uc <= 'X') return kPositionLUT[uc - 'C'];
  66   if (uc >= 'c' && uc <= 'x') return kPositionLUT[uc - 'c'];
  67   if (uc >= '2' && uc <= '9') return uc - '2';
  68   return -1;
  69 }