Better bitwise conversion

[dbeckwith]

Well one way you could do it is with a for loop, but that would only really be efficient if the bit masks are consecutive. I only know Java, so I might get the C++ syntax wrong, but here is what it might look like:

int keys = keysHeld();
byte packedKeys = 0;

for (int i = 0; i < 8; i++) {
  if (keys & (1 << i)) packedKeys |= 1 << i;
}

That would pack the values of the keys, but only if the bit masks were all in a line. You could also start the i variable at the first mask if it isn't zero. I have the same question as mikets though. Why do you even need to do this if keysHeld() already returns the key values? It seems redundant to me.

[mikets]

Originally Posted by dbeckwith

Well one way you could do it is with a for loop, but that would only really be efficient if the bit masks are consecutive. I only know Java, so I might get the C++ syntax wrong, but here is what it might look like:

int keys = keysHeld();
byte packedKeys = 0;
 
for (int i = 0; i < 8; i++) {
  if (keys & (1 << i)) packedKeys |= 1 << i;
}

That would pack the values of the keys, but only if the bit masks were all in a line. You could also start the i variable at the first mask if it isn't zero. I have the same question as mikets though. Why do you even need to do this if keysHeld() already returns the key values? It seems redundant to me.

But this for-loop is copying the exact same bit pattern from keys to packedKeys. So what's the difference between that and this?

packedKeys = keys;

[demosthenes2k8]

keys stores them differently, according to this:

typedef enum KEYPAD_BITS {
  KEY_A      = BIT(0),  //!< Keypad A button.
  KEY_B      = BIT(1),  //!< Keypad B button.
  KEY_SELECT = BIT(2),  //!< Keypad SELECT button.
  KEY_START  = BIT(3),  //!< Keypad START button.
  KEY_RIGHT  = BIT(4),  //!< Keypad RIGHT button.
  KEY_LEFT   = BIT(5),  //!< Keypad LEFT button.
  KEY_UP     = BIT(6),  //!< Keypad UP button.
  KEY_DOWN   = BIT(7),  //!< Keypad DOWN button.
  KEY_R      = BIT(8),  //!< Right shoulder button.
  KEY_L      = BIT(9),  //!< Left shoulder button.
  KEY_X      = BIT(10), //!< Keypad X button.
  KEY_Y      = BIT(11), //!< Keypad Y button.
  KEY_TOUCH  = BIT(12), //!< Touchscreen pendown.
  KEY_LID    = BIT(13)  //!< Lid state.
} KEYPAD_BITS;