Parse web color hexes for pallet (e.g. `0xFFAD63, ...`) (e.g. `#FFAD63, ...`)

palletColorParse.c

#include <stdio.h>
#include <stdint.h>

int palletColorParse(uint32_t *palletColor, const int palletColorSize, const char * parameterStr)
{
  // Parse web color hexes for pallet (e.g. `0xFFAD63, ...`) (e.g. `#FFAD63, ...`)
  // This was created for the cdecoder in https://github.com/mofosyne/arduino-gameboy-printer-emulator
  // https://gist.github.com/mofosyne/b1fc240b64c520c0bf3541a029e3dcc3
  // Brian Khuu 2021
  if (!parameterStr)
    return 0;
  int palletCounter = 0;
  int nibIndex = 0;
  uint32_t pallet = 0;
  char prevChar = 0;
  for ( ; (*(parameterStr)) != '\0' ; parameterStr++)
  {
    const char ch = *parameterStr;
    // Search for start of #XXXXXX, we are looking for 4 pallets
    if (nibIndex == 0)
    {
      if ((ch == '#') || ((prevChar == '0')&&(ch == 'x')))
      {
        pallet = 0;
        nibIndex = 3*2; // [R, G, B]
        prevChar = 0;
        continue;
      }
      prevChar = ch;
      continue;
    }
    nibIndex--;
    // Parse Nibble
    char nib = -1;
    if (('0' <= ch) && (ch <= '9'))
      nib = ch - '0';
    else if (('a' <= ch) && (ch <= 'f'))
      nib = ch - 'a' + 10;
    else if (('A' <= ch) && (ch <= 'F'))
      nib = ch - 'A' + 10;
    else
    {
      nibIndex = 0;
      palletColor[palletCounter] = pallet;
      palletCounter++;
      if (palletCounter >= palletColorSize)
        break;
      continue;
    }
    // Pallet
    pallet |= nib << (nibIndex*4);
    if (nibIndex == 0)
    {
      palletColor[palletCounter] = pallet;
      palletCounter++;
      if (palletCounter >= palletColorSize)
        break;
    }
  }
  return palletCounter;
}

void test(char *str)
{
  uint32_t palletColor[4] = {0,0,0,0};
  int count = palletColorParse(palletColor, sizeof(palletColor)/sizeof(palletColor[0]), str);
  printf("0x%06X, 0x%06X, 0x%06X, 0x%06X (parseCount %d) <-- '%s'\n", palletColor[0], palletColor[1], palletColor[2], palletColor[3], count, str);
}

int main (void)
{
  /*
    0xFFFFFF, 0xFFAD63, 0x833100, 0x000000 (parseCount 4) <-- '0xffffff, 0xffad63, 0x833100, 0x000000'
    0xFFFFFF, 0xFFAD63, 0x833100, 0x000000 (parseCount 4) <-- '#ffffff#ffad63#833100#000000'
    0xFFFFFF, 0xFFAD63, 0x833100, 0x000000 (parseCount 4) <-- '#ffffff, #ffad63, #833100, #000000'
    0xFAFAFA, 0xFAFAFA, 0xFAFAFA, 0xFAFAFA (parseCount 4) <-- '#fafafa  #fafafa  #fafafa  #fafafa  #fafafa'
    0xFFFFFF, 0xFFAD63, 0x833100, 0x000000 (parseCount 4) <-- '#ffffffff, #ffad63aa, #83310066, #00000088'
    0xFFFF00, 0xFFAD00, 0x833100, 0x000000 (parseCount 3) <-- '#ffff, #ffad, #8331, #0000'
    0xFF0000, 0xFF0000, 0x830000, 0x000000 (parseCount 3) <-- '#ff, #ff, #83, #00'
  */
  test("0xffffff, 0xffad63, 0x833100, 0x000000");
  test("#ffffff#ffad63#833100#000000");
  test("#ffffff, #ffad63, #833100, #000000");
  test("#fafafa  #fafafa  #fafafa  #fafafa  #fafafa");
  test("#ffffffff, #ffad63aa, #83310066, #00000088");
  test("#ffff, #ffad, #8331, #0000");
  test("#ff, #ff, #83, #00");
  return 0;
}