text: /**
   * The MIT License (MIT)
   *
   * Copyright (c) 2017 Richard Moore
   *
   * Permission is hereby granted, free of charge, to any person obtaining a copy
   * of this software and associated documentation files (the "Software"), to deal
   * in the Software without restriction, including without limitation the rights
   * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
   * copies of the Software, and to permit persons to whom the Software is
   * furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be included in
   * all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
   * THE SOFTWARE.
   */
  
  /**
   *  Special thanks to Nayuki (https://www.nayuki.io/) from which this library was
   *  heavily inspired and compared against.
   *
   *  See: https://github.com/nayuki/QR-Code-generator/tree/master/cpp
   */
  
  #include "qrcode.h"
  
  #include <stdlib.h>
  #include <string.h>
  #include <alloca.h>
  
  //#pragma mark - Error Correction Lookup tables
  
  #if LOCK_VERSION == 0
  
  static const uint16_t NUM_ERROR_CORRECTION_CODEWORDS[4][40] = {
      // 1,  2,  3,  4,  5,   6,   7,   8,   9,  10,  11,  12,  13,  14,  15,  16,  17,  18,  19,  20,  21,  22,  23,  24,   25,   26,   27,   28,   29,   30,   31,   32,   33,   34,   35,   36,   37,   38,   39,   40    Error correction level
      { 10, 16, 26, 36, 48,  64,  72,  88, 110, 130, 150, 176, 198, 216, 240, 280, 308, 338, 364, 416, 442, 476, 504, 560,  588,  644,  700,  728,  784,  812,  868,  924,  980, 1036, 1064, 1120, 1204, 1260, 1316, 1372},  // Medium
      {  7, 10, 15, 20, 26,  36,  40,  48,  60,  72,  80,  96, 104, 120, 132, 144, 168, 180, 196, 224, 224, 252, 270, 300,  312,  336,  360,  390,  420,  450,  480,  510,  540,  570,  570,  600,  630,  660,  720,  750},  // Low
      { 17, 28, 44, 64, 88, 112, 130, 156, 192, 224, 264, 308, 352, 384, 432, 480, 532, 588, 650, 700, 750, 816, 900, 960, 1050, 1110, 1200, 1260, 1350, 1440, 1530, 1620, 1710, 1800, 1890, 1980, 2100, 2220, 2310, 2430},  // High
      { 13, 22, 36, 52, 72,  96, 108, 132, 160, 192, 224, 260, 288, 320, 360, 408, 448, 504, 546, 600, 644, 690, 750, 810,  870,  952, 1020, 1050, 1140, 1200, 1290, 1350, 1440, 1530, 1590, 1680, 1770, 1860, 1950, 2040},  // Quartile
  };
  
  static const uint8_t NUM_ERROR_CORRECTION_BLOCKS[4][40] = {
      // Version: (note that index 0 is for padding, and is set to an illegal value)
      // 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40    Error correction level
      {  1, 1, 1, 2, 2, 4, 4, 4, 5, 5,  5,  8,  9,  9, 10, 10, 11, 13, 14, 16, 17, 17, 18, 20, 21, 23, 25, 26, 28, 29, 31, 33, 35, 37, 38, 40, 43, 45, 47, 49},  // Medium
      {  1, 1, 1, 1, 1, 2, 2, 2, 2, 4,  4,  4,  4,  4,  6,  6,  6,  6,  7,  8,  8,  9,  9, 10, 12, 12, 12, 13, 14, 15, 16, 17, 18, 19, 19, 20, 21, 22, 24, 25},  // Low
      {  1, 1, 2, 4, 4, 4, 5, 6, 8, 8, 11, 11, 16, 16, 18, 16, 19, 21, 25, 25, 25, 34, 30, 32, 35, 37, 40, 42, 45, 48, 51, 54, 57, 60, 63, 66, 70, 74, 77, 81},  // High
      {  1, 1, 2, 2, 4, 4, 6, 6, 8, 8,  8, 10, 12, 16, 12, 17, 16, 18, 21, 20, 23, 23, 25, 27, 29, 34, 34, 35, 38, 40, 43, 45, 48, 51, 53, 56, 59, 62, 65, 68},  // Quartile
  };
  
  static const uint16_t NUM_RAW_DATA_MODULES[40] = {
      //  1,   2,   3,   4,    5,    6,    7,    8,    9,   10,   11,   12,   13,   14,   15,   16,   17,
        208, 359, 567, 807, 1079, 1383, 1568, 1936, 2336, 2768, 3232, 3728, 4256, 4651, 5243, 5867, 6523,
      //   18,   19,   20,   21,    22,    23,    24,    25,   26,    27,     28,    29,    30,    31,
         7211, 7931, 8683, 9252, 10068, 10916, 11796, 12708, 13652, 14628, 15371, 16411, 17483, 18587,
      //    32,    33,    34,    35,    36,    37,    38,    39,    40
         19723, 20891, 22091, 23008, 24272, 25568, 26896, 28256, 29648
  };
  
  // @TODO: Put other LOCK_VERSIONS here
  #elif LOCK_VERSION == 3
  
  static const int16_t NUM_ERROR_CORRECTION_CODEWORDS[4] = {
      26, 15, 44, 36
  };
  
  static const int8_t NUM_ERROR_CORRECTION_BLOCKS[4] = {
      1, 1, 2, 2
  };
  
  static const uint16_t NUM_RAW_DATA_MODULES = 567;
  
  #else
  
  #error Unsupported LOCK_VERSION (add it...)
  
  #endif
  
  
  static int max(int a, int b) {
      if (a > b) { return a; }
      return b;
  }
  
  /*
  static int abs(int value) {
      if (value < 0) { return -value; }
      return value;
  }
  */
  
  
  //#pragma mark - Mode testing and conversion
  
  static int8_t getAlphanumeric(char c) {
      
      if (c >= '0' && c <= '9') { return (c - '0'); }
      if (c >= 'A' && c <= 'Z') { return (c - 'A' + 10); }
      
      switch (c) {
          case ' ': return 36;
          case '$': return 37;
          case '%': return 38;
          case '*': return 39;
          case '+': return 40;
          case '-': return 41;
          case '.': return 42;
          case '/': return 43;
          case ':': return 44;
      }
      
      return -1;
  }
  
  static bool isAlphanumeric(const char *text, uint16_t length) {
      while (length != 0) {
          if (getAlphanumeric(text[--length]) == -1) { return false; }
      }
      return true;
  }
  
  
  static bool isNumeric(const char *text, uint16_t length) {
      while (length != 0) {
          char c = text[--length];
          if (c < '0' || c > '9') { return false; }
      }
      return true;
  }
  
  
  //#pragma mark - Counting
  
  // We store the following tightly packed (less 8) in modeInfo
  //               <=9  <=26  <= 40
  // NUMERIC      ( 10,   12,    14);
  // ALPHANUMERIC (  9,   11,    13);
  // BYTE         (  8,   16,    16);
  static char getModeBits(uint8_t version, uint8_t mode) {
      // Note: We use 15 instead of 16; since 15 doesn't exist and we cannot store 16 (8 + 8) in 3 bits
      // hex(int("".join(reversed([('00' + bin(x - 8)[2:])[-3:] for x in [10, 9, 8, 12, 11, 15, 14, 13, 15]])), 2))
      unsigned int modeInfo = 0x7bbb80a;
      
  #if LOCK_VERSION == 0 || LOCK_VERSION > 9
      if (version > 9) { modeInfo >>= 9; }
  #endif
      
  #if LOCK_VERSION == 0 || LOCK_VERSION > 26
      if (version > 26) { modeInfo >>= 9; }
  #endif
      
      char result = 8 + ((modeInfo >> (3 * mode)) & 0x07);
      if (result == 15) { result = 16; }
      
      return result;
  }
  
  
  //#pragma mark - BitBucket
  
  typedef struct BitBucket {
      uint32_t bitOffsetOrWidth;
      uint16_t capacityBytes;
      uint8_t *data;
  } BitBucket;
  
  /*
  void bb_dump(BitBucket *bitBuffer) {
      printf("Buffer: ");
      for (uint32_t i = 0; i < bitBuffer->capacityBytes; i++) {
          printf("%02x", bitBuffer->data[i]);
          if ((i % 4) == 3) { printf(" "); }
      }
      printf("\n");
  }
  */
  
  static uint16_t bb_getGridSizeBytes(uint8_t size) {
      return (((size * size) + 7) / 8);
  }
  
  static uint16_t bb_getBufferSizeBytes(uint32_t bits) {
      return ((bits + 7) / 8);
  }
  
  static void bb_initBuffer(BitBucket *bitBuffer, uint8_t *data, int32_t capacityBytes) {
      bitBuffer->bitOffsetOrWidth = 0;
      bitBuffer->capacityBytes = capacityBytes;
      bitBuffer->data = data;
      
      memset(data, 0, bitBuffer->capacityBytes);
  }
  
  static void bb_initGrid(BitBucket *bitGrid, uint8_t *data, uint8_t size) {
      bitGrid->bitOffsetOrWidth = size;
      bitGrid->capacityBytes = bb_getGridSizeBytes(size);
      bitGrid->data = data;
  
      memset(data, 0, bitGrid->capacityBytes);
  }
  
  static void bb_appendBits(BitBucket *bitBuffer, uint32_t val, uint8_t length) {
      uint32_t offset = bitBuffer->bitOffsetOrWidth;
      for (int8_t i = length - 1; i >= 0; i--, offset++) {
          bitBuffer->data[offset >> 3] |= ((val >> i) & 1) << (7 - (offset & 7));
      }
      bitBuffer->bitOffsetOrWidth = offset;
  }
  /*
  void bb_setBits(BitBucket *bitBuffer, uint32_t val, int offset, uint8_t length) {
      for (int8_t i = length - 1; i >= 0; i--, offset++) {
          bitBuffer->data[offset >> 3] |= ((val >> i) & 1) << (7 - (offset & 7));
      }
  }
  */
  static void bb_setBit(BitBucket *bitGrid, uint8_t x, uint8_t y, bool on) {
      uint32_t offset = y * bitGrid->bitOffsetOrWidth + x;
      uint8_t mask = 1 << (7 - (offset & 0x07));
      if (on) {
          bitGrid->data[offset >> 3] |= mask;
      } else {
          bitGrid->data[offset >> 3] &= ~mask;
      }
  }
  
  static void bb_invertBit(BitBucket *bitGrid, uint8_t x, uint8_t y, bool invert) {
      uint32_t offset = y * bitGrid->bitOffsetOrWidth + x;
      uint8_t mask = 1 << (7 - (offset & 0x07));
      bool on = ((bitGrid->data[offset >> 3] & (1 << (7 - (offset & 0x07)))) != 0);
      if (on ^ invert) {
          bitGrid->data[offset >> 3] |= mask;
      } else {
          bitGrid->data[offset >> 3] &= ~mask;
      }
  }
  
  static bool bb_getBit(BitBucket *bitGrid, uint8_t x, uint8_t y) {
      uint32_t offset = y * bitGrid->bitOffsetOrWidth + x;
      return (bitGrid->data[offset >> 3] & (1 << (7 - (offset & 0x07)))) != 0;
  }
  
  
  //#pragma mark - Drawing Patterns
  
  // XORs the data modules in this QR Code with the given mask pattern. Due to XOR's mathematical
  // properties, calling applyMask(m) twice with the same value is equivalent to no change at all.
  // This means it is possible to apply a mask, undo it, and try another mask. Note that a final
  // well-formed QR Code symbol needs exactly one mask applied (not zero, not two, etc.).
  static void applyMask(BitBucket *modules, BitBucket *isFunction, uint8_t mask) {
      uint8_t size = modules->bitOffsetOrWidth;
      
      for (uint8_t y = 0; y < size; y++) {
          for (uint8_t x = 0; x < size; x++) {
              if (bb_getBit(isFunction, x, y)) { continue; }
              
              bool invert = 0;
              switch (mask) {
                  case 0:  invert = (x + y) % 2 == 0;                    break;
                  case 1:  invert = y % 2 == 0;                          break;
                  case 2:  invert = x % 3 == 0;                          break;
                  case 3:  invert = (x + y) % 3 == 0;                    break;
                  case 4:  invert = (x / 3 + y / 2) % 2 == 0;            break;
                  case 5:  invert = x * y % 2 + x * y % 3 == 0;          break;
                  case 6:  invert = (x * y % 2 + x * y % 3) % 2 == 0;    break;
                  case 7:  invert = ((x + y) % 2 + x * y % 3) % 2 == 0;  break;
              }
              bb_invertBit(modules, x, y, invert);
          }
      }
  }
  
  static void setFunctionModule(BitBucket *modules, BitBucket *isFunction, uint8_t x, uint8_t y, bool on) {
      bb_setBit(modules, x, y, on);
      bb_setBit(isFunction, x, y, true);
  }
  
  // Draws a 9*9 finder pattern including the border separator, with the center module at (x, y).
  static void drawFinderPattern(BitBucket *modules, BitBucket *isFunction, uint8_t x, uint8_t y) {
      uint8_t size = modules->bitOffsetOrWidth;
  
      for (int8_t i = -4; i <= 4; i++) {
          for (int8_t j = -4; j <= 4; j++) {
              uint8_t dist = max(abs(i), abs(j));  // Chebyshev/infinity norm
              int16_t xx = x + j, yy = y + i;
              if (0 <= xx && xx < size && 0 <= yy && yy < size) {
                  setFunctionModule(modules, isFunction, xx, yy, dist != 2 && dist != 4);
              }
          }
      }
  }
  
  // Draws a 5*5 alignment pattern, with the center module at (x, y).
  static void drawAlignmentPattern(BitBucket *modules, BitBucket *isFunction, uint8_t x, uint8_t y) {
      for (int8_t i = -2; i <= 2; i++) {
          for (int8_t j = -2; j <= 2; j++) {
              setFunctionModule(modules, isFunction, x + j, y + i, max(abs(i), abs(j)) != 1);
          }
      }
  }
  
  // Draws two copies of the format bits (with its own error correction code)
  // based on the given mask and this object's error correction level field.
  static void drawFormatBits(BitBucket *modules, BitBucket *isFunction, uint8_t ecc, uint8_t mask) {
      
      uint8_t size = modules->bitOffsetOrWidth;
  
      // Calculate error correction code and pack bits
      uint32_t data = ecc << 3 | mask;  // errCorrLvl is uint2, mask is uint3
      uint32_t rem = data;
      for (int i = 0; i < 10; i++) {
          rem = (rem << 1) ^ ((rem >> 9) * 0x537);
      }
      
      data = data << 10 | rem;
      data ^= 0x5412;  // uint15
      
      // Draw first copy
      for (uint8_t i = 0; i <= 5; i++) {
          setFunctionModule(modules, isFunction, 8, i, ((data >> i) & 1) != 0);
      }
      
      setFunctionModule(modules, isFunction, 8, 7, ((data >> 6) & 1) != 0);
      setFunctionModule(modules, isFunction, 8, 8, ((data >> 7) & 1) != 0);
      setFunctionModule(modules, isFunction, 7, 8, ((data >> 8) & 1) != 0);
      
      for (int8_t i = 9; i < 15; i++) {
          setFunctionModule(modules, isFunction, 14 - i, 8, ((data >> i) & 1) != 0);
      }
      
      // Draw second copy
      for (int8_t i = 0; i <= 7; i++) {
          setFunctionModule(modules, isFunction, size - 1 - i, 8, ((data >> i) & 1) != 0);
      }
      
      for (int8_t i = 8; i < 15; i++) {
          setFunctionModule(modules, isFunction, 8, size - 15 + i, ((data >> i) & 1) != 0);
      }
      
      setFunctionModule(modules, isFunction, 8, size - 8, true);
  }
  
  
  // Draws two copies of the version bits (with its own error correction code),
  // based on this object's version field (which only has an effect for 7 <= version <= 40).
  static void drawVersion(BitBucket *modules, BitBucket *isFunction, uint8_t version) {
      
      int8_t size = modules->bitOffsetOrWidth;
  
  #if LOCK_VERSION != 0 && LOCK_VERSION < 7
      return;
      
  #else
      if (version < 7) { return; }
      
      // Calculate error correction code and pack bits
      uint32_t rem = version;  // version is uint6, in the range [7, 40]
      for (uint8_t i = 0; i < 12; i++) {
          rem = (rem << 1) ^ ((rem >> 11) * 0x1F25);
      }
      
      uint32_t data = version << 12 | rem;  // uint18
      
      // Draw two copies
      for (uint8_t i = 0; i < 18; i++) {
          bool bit = ((data >> i) & 1) != 0;
          uint8_t a = size - 11 + i % 3, b = i / 3;
          setFunctionModule(modules, isFunction, a, b, bit);
          setFunctionModule(modules, isFunction, b, a, bit);
      }
      
  #endif
  }
  
  static void drawFunctionPatterns(BitBucket *modules, BitBucket *isFunction, uint8_t version, uint8_t ecc) {
      
      uint8_t size = modules->bitOffsetOrWidth;
  
      // Draw the horizontal and vertical timing patterns
      for (uint8_t i = 0; i < size; i++) {
          setFunctionModule(modules, isFunction, 6, i, i % 2 == 0);
          setFunctionModule(modules, isFunction, i, 6, i % 2 == 0);
      }
      
      // Draw 3 finder patterns (all corners except bottom right; overwrites some timing modules)
      drawFinderPattern(modules, isFunction, 3, 3);
      drawFinderPattern(modules, isFunction, size - 4, 3);
      drawFinderPattern(modules, isFunction, 3, size - 4);
      
  #if LOCK_VERSION == 0 || LOCK_VERSION > 1
  
      if (version > 1) {
  
          // Draw the numerous alignment patterns
          
          uint8_t alignCount = version / 7 + 2;
          uint8_t step;
          if (version != 32) {
              step = (version * 4 + alignCount * 2 + 1) / (2 * alignCount - 2) * 2;  // ceil((size - 13) / (2*numAlign - 2)) * 2
          } else { // C-C-C-Combo breaker!
              step = 26;
          }
          
          uint8_t alignPositionIndex = alignCount - 1;
          uint8_t alignPosition[alignCount];
          
          alignPosition[0] = 6;
          
          uint8_t size = version * 4 + 17;
          for (uint8_t i = 0, pos = size - 7; i < alignCount - 1; i++, pos -= step) {
              alignPosition[alignPositionIndex--] = pos;
          }
          
          for (uint8_t i = 0; i < alignCount; i++) {
              for (uint8_t j = 0; j < alignCount; j++) {
                  if ((i == 0 && j == 0) || (i == 0 && j == alignCount - 1) || (i == alignCount - 1 && j == 0)) {
                      continue;  // Skip the three finder corners
                  } else {
                      drawAlignmentPattern(modules, isFunction, alignPosition[i], alignPosition[j]);
                  }
              }
          }
      }
      
  #endif
      
      // Draw configuration data
      drawFormatBits(modules, isFunction, ecc, 0);  // Dummy mask value; overwritten later in the constructor
      drawVersion(modules, isFunction, version);
  }
  
  
  // Draws the given sequence of 8-bit codewords (data and error correction) onto the entire
  // data area of this QR Code symbol. Function modules need to be marked off before this is called.
  static void drawCodewords(BitBucket *modules, BitBucket *isFunction, BitBucket *codewords) {
      
      uint32_t bitLength = codewords->bitOffsetOrWidth;
      uint8_t *data = codewords->data;
      
      uint8_t size = modules->bitOffsetOrWidth;
      
      // Bit index into the data
      uint32_t i = 0;
      
      // Do the funny zigzag scan
      for (int16_t right = size - 1; right >= 1; right -= 2) {  // Index of right column in each column pair
          if (right == 6) { right = 5; }
          
          for (uint8_t vert = 0; vert < size; vert++) {  // Vertical counter
              for (int j = 0; j < 2; j++) {
                  uint8_t x = right - j;  // Actual x coordinate
                  bool upwards = ((right & 2) == 0) ^ (x < 6);
                  uint8_t y = upwards ? size - 1 - vert : vert;  // Actual y coordinate
                  if (!bb_getBit(isFunction, x, y) && i < bitLength) {
                      bb_setBit(modules, x, y, ((data[i >> 3] >> (7 - (i & 7))) & 1) != 0);
                      i++;
                  }
                  // If there are any remainder bits (0 to 7), they are already
                  // set to 0/false/white when the grid of modules was initialized
              }
          }
      }
  }
  
  
  
  //#pragma mark - Penalty Calculation
  
  #define PENALTY_N1      3
  #define PENALTY_N2      3
  #define PENALTY_N3     40
  #define PENALTY_N4     10
  
  // Calculates and returns the penalty score based on state of this QR Code's current modules.
  // This is used by the automatic mask choice algorithm to find the mask pattern that yields the lowest score.
  // @TODO: This can be optimized by working with the bytes instead of bits.
  static uint32_t getPenaltyScore(BitBucket *modules) {
      uint32_t result = 0;
      
      uint8_t size = modules->bitOffsetOrWidth;
      
      // Adjacent modules in row having same color
      for (uint8_t y = 0; y < size; y++) {
          
          bool colorX = bb_getBit(modules, 0, y);
          for (uint8_t x = 1, runX = 1; x < size; x++) {
              bool cx = bb_getBit(modules, x, y);
              if (cx != colorX) {
                  colorX = cx;
                  runX = 1;
                  
              } else {
                  runX++;
                  if (runX == 5) {
                      result += PENALTY_N1;
                  } else if (runX > 5) {
                      result++;
                  }
              }
          }
      }
      
      // Adjacent modules in column having same color
      for (uint8_t x = 0; x < size; x++) {
          bool colorY = bb_getBit(modules, x, 0);
          for (uint8_t y = 1, runY = 1; y < size; y++) {
              bool cy = bb_getBit(modules, x, y);
              if (cy != colorY) {
                  colorY = cy;
                  runY = 1;
              } else {
                  runY++;
                  if (runY == 5) {
                      result += PENALTY_N1;
                  } else if (runY > 5) {
                      result++;
                  }
              }
          }
      }
      
      uint16_t black = 0;
      for (uint8_t y = 0; y < size; y++) {
          uint16_t bitsRow = 0, bitsCol = 0;
          for (uint8_t x = 0; x < size; x++) {
              bool color = bb_getBit(modules, x, y);
  
              // 2*2 blocks of modules having same color
              if (x > 0 && y > 0) {
                  bool colorUL = bb_getBit(modules, x - 1, y - 1);
                  bool colorUR = bb_getBit(modules, x, y - 1);
                  bool colorL = bb_getBit(modules, x - 1, y);
                  if (color == colorUL && color == colorUR && color == colorL) {
                      result += PENALTY_N2;
                  }
              }
  
              // Finder-like pattern in rows and columns
              bitsRow = ((bitsRow << 1) & 0x7FF) | color;
              bitsCol = ((bitsCol << 1) & 0x7FF) | bb_getBit(modules, y, x);
  
              // Needs 11 bits accumulated
              if (x >= 10) {
                  if (bitsRow == 0x05D || bitsRow == 0x5D0) {
                      result += PENALTY_N3;
                  }
                  if (bitsCol == 0x05D || bitsCol == 0x5D0) {
                      result += PENALTY_N3;
                  }
              }
  
              // Balance of black and white modules
              if (color) { black++; }
          }
      }
  
      // Find smallest k such that (45-5k)% <= dark/total <= (55+5k)%
      uint16_t total = size * size;
      for (uint16_t k = 0; black * 20 < (9 - k) * total || black * 20 > (11 + k) * total; k++) {
          result += PENALTY_N4;
      }
      
      return result;
  }
  
  
  //#pragma mark - Reed-Solomon Generator
  
  static uint8_t rs_multiply(uint8_t x, uint8_t y) {
      // Russian peasant multiplication
      // See: https://en.wikipedia.org/wiki/Ancient_Egyptian_multiplication
      uint16_t z = 0;
      for (int8_t i = 7; i >= 0; i--) {
          z = (z << 1) ^ ((z >> 7) * 0x11D);
          z ^= ((y >> i) & 1) * x;
      }
      return z;
  }
  
  static void rs_init(uint8_t degree, uint8_t *coeff) {
      memset(coeff, 0, degree);
      coeff[degree - 1] = 1;
      
      // Compute the product polynomial (x - r^0) * (x - r^1) * (x - r^2) * ... * (x - r^{degree-1}),
      // drop the highest term, and store the rest of the coefficients in order of descending powers.
      // Note that r = 0x02, which is a generator element of this field GF(2^8/0x11D).
      uint16_t root = 1;
      for (uint8_t i = 0; i < degree; i++) {
          // Multiply the current product by (x - r^i)
          for (uint8_t j = 0; j < degree; j++) {
              coeff[j] = rs_multiply(coeff[j], root);
              if (j + 1 < degree) {
                  coeff[j] ^= coeff[j + 1];
              }
          }
          root = (root << 1) ^ ((root >> 7) * 0x11D);  // Multiply by 0x02 mod GF(2^8/0x11D)
      }
  }
  
  static void rs_getRemainder(uint8_t degree, uint8_t *coeff, uint8_t *data, uint8_t length, uint8_t *result, uint8_t stride) {
      // Compute the remainder by performing polynomial division
      
      //for (uint8_t i = 0; i < degree; i++) { result[] = 0; }
      //memset(result, 0, degree);
      
      for (uint8_t i = 0; i < length; i++) {
          uint8_t factor = data[i] ^ result[0];
          for (uint8_t j = 1; j < degree; j++) {
              result[(j - 1) * stride] = result[j * stride];
          }
          result[(degree - 1) * stride] = 0;
          
          for (uint8_t j = 0; j < degree; j++) {
              result[j * stride] ^= rs_multiply(coeff[j], factor);
          }
      }
  }
  
  
  
  //#pragma mark - QrCode
  
  static int8_t encodeDataCodewords(BitBucket *dataCodewords, const uint8_t *text, uint16_t length, uint8_t version) {
      int8_t mode = MODE_BYTE;
      
      if (isNumeric((char*)text, length)) {
          mode = MODE_NUMERIC;
          bb_appendBits(dataCodewords, 1 << MODE_NUMERIC, 4);
          bb_appendBits(dataCodewords, length, getModeBits(version, MODE_NUMERIC));
  
          uint16_t accumData = 0;
          uint8_t accumCount = 0;
          for (uint16_t i = 0; i < length; i++) {
              accumData = accumData * 10 + ((char)(text[i]) - '0');
              accumCount++;
              if (accumCount == 3) {
                  bb_appendBits(dataCodewords, accumData, 10);
                  accumData = 0;
                  accumCount = 0;
              }
          }
          
          // 1 or 2 digits remaining
          if (accumCount > 0) {
              bb_appendBits(dataCodewords, accumData, accumCount * 3 + 1);
          }
          
      } else if (isAlphanumeric((char*)text, length)) {
          mode = MODE_ALPHANUMERIC;
          bb_appendBits(dataCodewords, 1 << MODE_ALPHANUMERIC, 4);
          bb_appendBits(dataCodewords, length, getModeBits(version, MODE_ALPHANUMERIC));
  
          uint16_t accumData = 0;
          uint8_t accumCount = 0;
          for (uint16_t i = 0; i  < length; i++) {
              accumData = accumData * 45 + getAlphanumeric((char)(text[i]));
              accumCount++;
              if (accumCount == 2) {
                  bb_appendBits(dataCodewords, accumData, 11);
                  accumData = 0;
                  accumCount = 0;
              }
          }
          
          // 1 character remaining
          if (accumCount > 0) {
              bb_appendBits(dataCodewords, accumData, 6);
          }
          
      } else {
          bb_appendBits(dataCodewords, 1 << MODE_BYTE, 4);
          bb_appendBits(dataCodewords, length, getModeBits(version, MODE_BYTE));
          for (uint16_t i = 0; i < length; i++) {
              bb_appendBits(dataCodewords, (char)(text[i]), 8);
          }
      }
      
      //bb_setBits(dataCodewords, length, 4, getModeBits(version, mode));
      
      return mode;
  }
  
  static void performErrorCorrection(uint8_t version, uint8_t ecc, BitBucket *data) {
      
      // See: http://www.thonky.com/qr-code-tutorial/structure-final-message
      
  #if LOCK_VERSION == 0
      uint8_t numBlocks = NUM_ERROR_CORRECTION_BLOCKS[ecc][version - 1];
      uint16_t totalEcc = NUM_ERROR_CORRECTION_CODEWORDS[ecc][version - 1];
      uint16_t moduleCount = NUM_RAW_DATA_MODULES[version - 1];
  #else
      uint8_t numBlocks = NUM_ERROR_CORRECTION_BLOCKS[ecc];
      uint16_t totalEcc = NUM_ERROR_CORRECTION_CODEWORDS[ecc];
      uint16_t moduleCount = NUM_RAW_DATA_MODULES;
  #endif
      
      uint8_t blockEccLen = totalEcc / numBlocks;
      uint8_t numShortBlocks = numBlocks - moduleCount / 8 % numBlocks;
      uint8_t shortBlockLen = moduleCount / 8 / numBlocks;
      
      uint8_t shortDataBlockLen = shortBlockLen - blockEccLen;
      
  //    uint8_t result[data->capacityBytes];
  //    memset(result, 0, sizeof(result));
      uint8_t *result = alloca(data->capacityBytes);
      memset(result, 0, data->capacityBytes);    
      
  //    uint8_t coeff[blockEccLen];
      uint8_t *coeff = alloca(blockEccLen);
      rs_init(blockEccLen, coeff);
      
      uint16_t offset = 0;
      uint8_t *dataBytes = data->data;
      
      
      // Interleave all short blocks
      for (uint8_t i = 0; i < shortDataBlockLen; i++) {
          uint16_t index = i;
          uint8_t stride = shortDataBlockLen;
          for (uint8_t blockNum = 0; blockNum < numBlocks; blockNum++) {
              result[offset++] = dataBytes[index];
              
  #if LOCK_VERSION == 0 || LOCK_VERSION >= 5
              if (blockNum == numShortBlocks) { stride++; }
  #endif
              index += stride;
          }
      }
      
      // Version less than 5 only have short blocks
  #if LOCK_VERSION == 0 || LOCK_VERSION >= 5
      {
          // Interleave long blocks
          uint16_t index = shortDataBlockLen * (numShortBlocks + 1);
          uint8_t stride = shortDataBlockLen;
          for (uint8_t blockNum = 0; blockNum < numBlocks - numShortBlocks; blockNum++) {
              result[offset++] = dataBytes[index];
              
              if (blockNum == 0) { stride++; }
              index += stride;
          }
      }
  #endif
      
      // Add all ecc blocks, interleaved
      uint8_t blockSize = shortDataBlockLen;
      for (uint8_t blockNum = 0; blockNum < numBlocks; blockNum++) {
          
  #if LOCK_VERSION == 0 || LOCK_VERSION >= 5
          if (blockNum == numShortBlocks) { blockSize++; }
  #endif
          rs_getRemainder(blockEccLen, coeff, dataBytes, blockSize, &result[offset + blockNum], numBlocks);
          dataBytes += blockSize;
      }
      
      memcpy(data->data, result, data->capacityBytes);
      data->bitOffsetOrWidth = moduleCount;
  }
  
  // We store the Format bits tightly packed into a single byte (each of the 4 modes is 2 bits)
  // The format bits can be determined by ECC_FORMAT_BITS >> (2 * ecc)
  static const uint8_t ECC_FORMAT_BITS = (0x02 << 6) | (0x03 << 4) | (0x00 << 2) | (0x01 << 0);
  
  
  //#pragma mark - Public QRCode functions
  
  uint16_t qrcode_getBufferSize(uint8_t version) {
      return bb_getGridSizeBytes(4 * version + 17);
  }
  
  // @TODO: Return error if data is too big.
  int8_t qrcode_initBytes(QRCode *qrcode, uint8_t *modules, uint8_t version, uint8_t ecc, uint8_t *data, uint16_t length) {
      uint8_t size = version * 4 + 17;
      qrcode->version = version;
      qrcode->size = size;
      qrcode->ecc = ecc;
      qrcode->modules = modules;
      
      uint8_t eccFormatBits = (ECC_FORMAT_BITS >> (2 * ecc)) & 0x03;
      
  #if LOCK_VERSION == 0
      uint16_t moduleCount = NUM_RAW_DATA_MODULES[version - 1];
      uint16_t dataCapacity = moduleCount / 8 - NUM_ERROR_CORRECTION_CODEWORDS[eccFormatBits][version - 1];
  #else
      version = LOCK_VERSION;
      uint16_t moduleCount = NUM_RAW_DATA_MODULES;
      uint16_t dataCapacity = moduleCount / 8 - NUM_ERROR_CORRECTION_CODEWORDS[eccFormatBits];
  #endif
      
      struct BitBucket codewords;
  //    uint8_t codewordBytes[bb_getBufferSizeBytes(moduleCount)];  
  //    bb_initBuffer(&codewords, codewordBytes, (int32_t)sizeof(codewordBytes));
      uint8_t *codewordBytes = alloca(bb_getBufferSizeBytes(moduleCount));
      bb_initBuffer(&codewords, codewordBytes, bb_getBufferSizeBytes(moduleCount));
  
      // Place the data code words into the buffer
      int8_t mode = encodeDataCodewords(&codewords, data, length, version);
      
      if (mode < 0) { return -1; }
      qrcode->mode = mode;
      
      // Add terminator and pad up to a byte if applicable
      uint32_t padding = (dataCapacity * 8) - codewords.bitOffsetOrWidth;
      if (padding > 4) { padding = 4; }
      bb_appendBits(&codewords, 0, padding);
      bb_appendBits(&codewords, 0, (8 - codewords.bitOffsetOrWidth % 8) % 8);
  
      // Pad with alternate bytes until data capacity is reached
      for (uint8_t padByte = 0xEC; codewords.bitOffsetOrWidth < (dataCapacity * 8); padByte ^= 0xEC ^ 0x11) {
          bb_appendBits(&codewords, padByte, 8);
      }
  
      BitBucket modulesGrid;
      bb_initGrid(&modulesGrid, modules, size);
      
      BitBucket isFunctionGrid;
  //    uint8_t isFunctionGridBytes[bb_getGridSizeBytes(size)];
      uint8_t *isFunctionGridBytes = alloca(bb_getGridSizeBytes(size));
      bb_initGrid(&isFunctionGrid, isFunctionGridBytes, size);
      
      // Draw function patterns, draw all codewords, do masking
      drawFunctionPatterns(&modulesGrid, &isFunctionGrid, version, eccFormatBits);
      performErrorCorrection(version, eccFormatBits, &codewords);
      drawCodewords(&modulesGrid, &isFunctionGrid, &codewords);
      
      // Find the best (lowest penalty) mask
      uint8_t mask = 0;
      int32_t minPenalty = INT32_MAX;
      for (uint8_t i = 0; i < 8; i++) {
          drawFormatBits(&modulesGrid, &isFunctionGrid, eccFormatBits, i);
          applyMask(&modulesGrid, &isFunctionGrid, i);
          int penalty = getPenaltyScore(&modulesGrid);
          if (penalty < minPenalty) {
              mask = i;
              minPenalty = penalty;
          }
          applyMask(&modulesGrid, &isFunctionGrid, i);  // Undoes the mask due to XOR
      }
      
      qrcode->mask = mask;
      
      // Overwrite old format bits
      drawFormatBits(&modulesGrid, &isFunctionGrid, eccFormatBits, mask);
      
      // Apply the final choice of mask
      applyMask(&modulesGrid, &isFunctionGrid, mask);
  
      return 0;
  }
  
  int8_t qrcode_initText(QRCode *qrcode, uint8_t *modules, uint8_t version, uint8_t ecc, const char *data) {
      return qrcode_initBytes(qrcode, modules, version, ecc, (uint8_t*)data, strlen(data));
  }
  
  bool qrcode_getModule(QRCode *qrcode, uint8_t x, uint8_t y) {
      if (x >= qrcode->size || y >= qrcode->size) {
          return false;
      }
  
      uint32_t offset = y * qrcode->size + x;
      return (qrcode->modules[offset >> 3] & (1 << (7 - (offset & 0x07)))) != 0;
  }
  
  /*
  uint8_t qrcode_getHexLength(QRCode *qrcode) {
      return ((qrcode->size * qrcode->size) + 7) / 4;
  }
  
  void qrcode_getHex(QRCode *qrcode, char *result) {
      
  }
  */
  