#include <FastLED.h>

CRGBArray<110> leds;

void setup() {
  FastLED.addLeds<WS2812B, PB1, GRB>(leds, leds.size());
}

uint32_t seed = 0x5eed517;
void loop() {
  const auto fades = 128; // number of simultaneous fades
  seed -= 0x2a08c07 * 2 * (fades - 1); // rewind PRNG by N-1 fades
  uint16_t v16 = 0; // accumulator for Value/Brightness
  for (auto i = 0; i < fades; i++) {
    uint16_t rnd = hash16();
    uint8_t h = rnd >> 8;
    uint8_t s = rnd;
    uint8_t v = v16 >> 8;
    if (v < 128) v *= 2; // fade out
    else v = 255 - 2 * v; // fade in
    leds[hash16() % leds.size()] += CHSV(h, s, v);
    v16 += 65536 / fades;
  }
  FastLED.show();
  FastLED.clear();
}

// a simple 16-bit PRNG using a 32-bit seed
uint16_t hash16() {
  seed += 0x2a08c07;
  return (seed >> 16) ^ (uint16_t)seed;
}