Get led code

<source lang='cpp'> /**

* A data structure for a sparse representation of values in a LED string.
*
* A non-sparse representation of an LED string holds 3 bytes for every
* LED in the string. For a 60 LED string this means that at least 180 bytes
* of memory are required.
*
* This type also has a buffer of bytes, but these bytes hold sequences of
* the form:
* <jump>, <count>, G1, R1, B1, G2, R2, B2, <jump>, <count>, G3, R3, B3, etc...
*
* <jump> represents an amount of black pixels, <count> is the number of GRB values
* that follow
*
* A buffer is terminated by a zero <jump> value or a zero <count>. The first <jump>
* never terminates the sequence, even if it is zero. A zero <jump> count at the start
* means the string starts with a lit LED.
*/

template<uint8_t buffer_size, uint8_t led_string_size> struct sparse_leds { uint8_t buffer[buffer_size];

/// move the range [begin, end> towards buffer_end. /// buffer_end must be higher than end, for this function to work correctly. /// The bytes that become available are filled with zeros. static void move_right( uint8_t *begin, uint8_t *end, uint8_t *buffer_end) { while (begin < end) *(--buffer_end) = *(--end); while( begin < buffer_end) *(--buffer_end) = 0; } };

/**

* specialization of the led_buffer_traits for sparse buffers.
*
* For regular arrays, the led string size is simply the number of bytes
* divided by three. A sparse buffer has the number of leds encoded in the
* type as a template argument.
*/

template< uint8_t buffer_size, uint8_t led_string_size> struct led_buffer_traits<sparse_leds<buffer_size, led_string_size> > { static const uint8_t count = led_string_size; static const uint8_t size = buffer_size; };

/**

* clear a sparse buffer. This fills the buffer with as many
* black leds as there are leds in the string.
*/

template<uint8_t buffer_size, uint8_t led_string_size> inline void clear( sparse_leds<buffer_size, led_string_size> &leds) { leds.buffer[0] = led_string_size; leds.buffer[1] = 0; }

/**

* Given a sparse buffer and a position in the LED string, find the position in
* the buffer that corresponds with this LED. If such a position did not exist, it
* will be created by introducing a new block inside the buffer or by appending
* a location for the LED at the start or end of an existing block.
*
* This function assumes that the current buffer already covers the complete LED
* string, or in other words, the sum of all <jump> and <count> values must be higher
* than the argument 'position' to this function. This function makes sure that
* the sum of <jump>s and <count>s remains the same.
*
* This function is deliberately not implemented as an operator[] of sparse_leds, because
* using an explicit function call makes it clear that code is being run and that it is
* worthwhile to store the result of this function instead of calling the function twice.
* Measurements have shown that the compiler will not memoize a second call to this function with
* the same arguments.
*/

template<uint8_t buffer_size, uint8_t led_string_size> rgb & get( sparse_leds<buffer_size, led_string_size> &leds, uint8_t position) {

uint8_t *buffer_iterator = &leds.buffer[0]; uint8_t * const end = buffer_iterator + buffer_size; uint8_t current_pos = 0; while (buffer_iterator < end) { // current_pos pointing one past the previous block // buffer_iterator pointing at a 'jump'

uint8_t jump_pos = current_pos + *buffer_iterator; if (jump_pos > position + 1) { // need to add a new block before the one we're pointing at. *buffer_iterator = (jump_pos - position - 1); leds.move_right( buffer_iterator, end - 5, end); *buffer_iterator++ = position - current_pos; *buffer_iterator++=1; break; } current_pos = jump_pos; // current_pos now pointing at the location of the first led in the block if (current_pos == position + 1) { // prepend the new led to the current block of leds --(*buffer_iterator); ++buffer_iterator; ++*buffer_iterator; ++buffer_iterator; leds.move_right( buffer_iterator, end-3, end); break; } ++buffer_iterator; // pointing at the led block size jump_pos = position - current_pos; if ( jump_pos < *buffer_iterator) { // we're actually pointing to a led that is inside the current block buffer_iterator += (1 + 3 * jump_pos); break; } current_pos += *buffer_iterator; // pointing one past the last led in the string. jump_pos = 3 * (*buffer_iterator) + 1; //buffer_iterator += 3 * (*buffer_iterator); if (position == current_pos) { // decrease distance between this block and the next by one if (--(*(buffer_iterator+jump_pos)) == 0) { // distance is zero, concatenate two blocks.

// new size is the old size plus the size of the next block plus // 1 for the new led. *buffer_iterator += *(buffer_iterator + jump_pos + 1)+1; buffer_iterator += jump_pos; leds.move_right( buffer_iterator, end - 1, end); } else { // distance is non-zero, just enlarge the current block ++*buffer_iterator; buffer_iterator += jump_pos; leds.move_right( buffer_iterator, end - 3, end); } break; } buffer_iterator+=jump_pos; }

return *(reinterpret_cast<rgb *>(buffer_iterator)); } </source>