/* ------------------------------------------------------------------------- */

static int _glewExtensionCompare(const void *a, const void *b)
{
  /* http://www.chanduthedev.com/2012/07/strcmp-implementation-in-c.html */
  const char *s1 = (const char *) a;
  const char *s2 = (const char *) b;
  while (*s1 || *s2)
  {
      if (*s1 > *s2)
          return 1;
      if (*s1 < *s2)
          return -1;
      s1++;
      s2++;
  }
  return 0;
}

static GLboolean *_glewGetExtensionString(const char *name)
{
  const char **n = (const char **) bsearch(name, _glewExtensionLookup, sizeof(_glewExtensionLookup)/sizeof(char *)-1, sizeof(char *), _glewExtensionCompare);
  ptrdiff_t i;

  if (n)
  {
      i = n-_glewExtensionLookup;
      return _glewExtensionString+i;
  }

  return NULL;
}

static GLboolean *_glewGetExtensionEnable(const char *name)
{
  const char **n = (const char **) bsearch(name, _glewExtensionLookup, sizeof(_glewExtensionLookup)/sizeof(char *)-1, sizeof(char *), _glewExtensionCompare);
  ptrdiff_t i;

  if (n)
  {
      i = n-_glewExtensionLookup;
      return _glewExtensionEnabled[i];
  }

  return NULL;
}

static const char *_glewNextSpace(const char *i)
{
  const char *j = i;
  if (j)
    while (*j!=' ' && *j) ++j;
  return j;
}

static const char *_glewNextNonSpace(const char *i)
{
  const char *j = i;
  if (j)
    while (*j==' ') ++j;
  return j;
}

GLboolean GLEWAPIENTRY glewGetExtension (const char* name)
{
  GLboolean *enable = _glewGetExtensionString(name);
  if (enable)
    return *enable;
  return GL_FALSE;
}

/* ------------------------------------------------------------------------- */

static GLenum GLEWAPIENTRY glewContextInit ()
{
  const GLubyte* s;
  GLuint dot;
  GLint major, minor;

  /* query opengl version */
  s = glGetString(GL_VERSION);
  dot = _glewStrCLen(s, '.');
  if (dot == 0)
    return GLEW_ERROR_NO_GL_VERSION;

  major = s[dot-1]-'0';
  minor = s[dot+1]-'0';

  if (minor < 0 || minor > 9)
    minor = 0;
  if (major<0 || major>9)
    return GLEW_ERROR_NO_GL_VERSION;

  if (major == 1 && minor == 0)
  {
    return GLEW_ERROR_GL_VERSION_10_ONLY;
  }
  else
  {
    GLEW_VERSION_4_5   = ( major > 4 )                 || ( major == 4 && minor >= 5 ) ? GL_TRUE : GL_FALSE;
    GLEW_VERSION_4_4   = GLEW_VERSION_4_5   == GL_TRUE || ( major == 4 && minor >= 4 ) ? GL_TRUE : GL_FALSE;
    GLEW_VERSION_4_3   = GLEW_VERSION_4_4   == GL_TRUE || ( major == 4 && minor >= 3 ) ? GL_TRUE : GL_FALSE;
    GLEW_VERSION_4_2   = GLEW_VERSION_4_3   == GL_TRUE || ( major == 4 && minor >= 2 ) ? GL_TRUE : GL_FALSE;
    GLEW_VERSION_4_1   = GLEW_VERSION_4_2   == GL_TRUE || ( major == 4 && minor >= 1 ) ? GL_TRUE : GL_FALSE;
    GLEW_VERSION_4_0   = GLEW_VERSION_4_1   == GL_TRUE || ( major == 4               ) ? GL_TRUE : GL_FALSE;
    GLEW_VERSION_3_3   = GLEW_VERSION_4_0   == GL_TRUE || ( major == 3 && minor >= 3 ) ? GL_TRUE : GL_FALSE;
    GLEW_VERSION_3_2   = GLEW_VERSION_3_3   == GL_TRUE || ( major == 3 && minor >= 2 ) ? GL_TRUE : GL_FALSE;
    GLEW_VERSION_3_1   = GLEW_VERSION_3_2   == GL_TRUE || ( major == 3 && minor >= 1 ) ? GL_TRUE : GL_FALSE;
    GLEW_VERSION_3_0   = GLEW_VERSION_3_1   == GL_TRUE || ( major == 3               ) ? GL_TRUE : GL_FALSE;
    GLEW_VERSION_2_1   = GLEW_VERSION_3_0   == GL_TRUE || ( major == 2 && minor >= 1 ) ? GL_TRUE : GL_FALSE;
    GLEW_VERSION_2_0   = GLEW_VERSION_2_1   == GL_TRUE || ( major == 2               ) ? GL_TRUE : GL_FALSE;
    GLEW_VERSION_1_5   = GLEW_VERSION_2_0   == GL_TRUE || ( major == 1 && minor >= 5 ) ? GL_TRUE : GL_FALSE;
    GLEW_VERSION_1_4   = GLEW_VERSION_1_5   == GL_TRUE || ( major == 1 && minor >= 4 ) ? GL_TRUE : GL_FALSE;
    GLEW_VERSION_1_3   = GLEW_VERSION_1_4   == GL_TRUE || ( major == 1 && minor >= 3 ) ? GL_TRUE : GL_FALSE;
    GLEW_VERSION_1_2_1 = GLEW_VERSION_1_3   == GL_TRUE                                 ? GL_TRUE : GL_FALSE;
    GLEW_VERSION_1_2   = GLEW_VERSION_1_2_1 == GL_TRUE || ( major == 1 && minor >= 2 ) ? GL_TRUE : GL_FALSE;
    GLEW_VERSION_1_1   = GLEW_VERSION_1_2   == GL_TRUE || ( major == 1 && minor >= 1 ) ? GL_TRUE : GL_FALSE;
  }

  memset(_glewExtensionString,0,sizeof(_glewExtensionString));

  if (GLEW_VERSION_3_0)
  {
    GLint n = 0;
    GLint i;
    PFNGLGETSTRINGIPROC getStringi;
    const char *ext;
    GLboolean *enable;

    glGetIntegerv(GL_NUM_EXTENSIONS, &n);

    /* glGetStringi is OpenGL 3.0 */
    getStringi = (PFNGLGETSTRINGIPROC) glewGetProcAddress((const GLubyte*)"glGetStringi");
    if (getStringi)
      for (i = 0; i<n; ++i)
      {
        ext = (const char *) getStringi(GL_EXTENSIONS, i);

        /* Based on extension string(s), glewGetExtension purposes */
        enable = _glewGetExtensionString(ext);
        if (enable)
          *enable = GL_TRUE;

        /* Based on extension string(s), experimental mode, glewIsSupported purposes */
        enable = _glewGetExtensionEnable(ext);
        if (enable)
          *enable = GL_TRUE;
      }
  }
  else
  {
    const char *extensions;
    const char *end;
    const char *i;
    const char *j;
    char ext[128];
    GLboolean *enable;

    extensions = (const char *) glGetString(GL_EXTENSIONS);

    if (extensions)
    {
      end = extensions + _glewStrLen((const GLubyte *) extensions);
      for (i=extensions; i<end; i = j + 1)
      {
        i = _glewNextNonSpace(i);
        j = _glewNextSpace(i);

        /* Copy extension into NUL terminated string */
        if (j-i >= (ptrdiff_t) sizeof(ext))
          continue;
        _glewStrCopy(ext, i, ' ');

        /* Based on extension string(s), glewGetExtension purposes */
        enable = _glewGetExtensionString(ext);
        if (enable)
          *enable = GL_TRUE;

        /* Based on extension string(s), experimental mode, glewIsSupported purposes */
        enable = _glewGetExtensionEnable(ext);
        if (enable)
          *enable = GL_TRUE;
      }
    }
  }