#!/usr/bin/ruby

#
## http://rosettacode.org/wiki/Perlin_noise
#

const p = (%w'47 4G 3T 2J 2I F 3N D 5L 2N 2O 1H 5E 6H 7 69 3W 10 2V U 1X 3Y 8
2R 11 6O L A N 5A 6 44 6V 3C 6I 23 0 Q 5H 1Q 2M 70 63 5N 39 Z B W 1L 4X X 2G
6L 45 1K 2F 4U K 3H 3S 4R 4O 1W 4V 22 4L 1Z 3Q 3V 1C R 4M 25 42 4E 6F 2B 33 6D
3E 1O 5V 3P 6E 64 2X 2K 15 1J 1A 6T 14 6S 2U 3Z 1I 1T P 1R 4H 1 60 28 21 5T 24
3O 57 5S 2H I 4P 5K 5G 3R 3M 38 58 4F 2E 4K 2S 31 5I 4T 56 3 1S 1G 61 6A 6Y 3G
3F 5 5M 12 43 3A 3I 73 2A 2D 5W 5R 5Q 1N 6B 1B G 1M H 52 59 S 16 67 53 4Q 5X
3B 6W 48 2 18 4A 4J 1Y 65 49 2T 4B 4N 17 4S 9 3L M 13 71 J 2Q 30 32 27 35 68
6G 4Y 55 34 2W 62 6U 2P 6C 6Z Y 6Q 5D 6M 5U 40 C 5B 4Z 4I 6P 29 1F 41 6J 6X E
6N 2Z 1D 5C 5Y V 51 5J 2Y 4D 54 2C 5O 4W 37 3D 1E 19 3J 4 46 72 3U 6K 5P 2L 66
36 1V T O 20 6R 3X 3K 5F 26 1U 5Z 1P 4C 50' * 2 -> map {|n| Num(n, 36) })

func fade(n) { n * n * n * (n * (n * 6 - 15) + 10) }
func lerp(t, a, b) { a + t*(b-a) }

func grad(h, x, y, z) {
    h &= 15
    var u = (h < 8 ? x : y)
    var v = (h < 4 ? y : (h ~~ [12,14] ? x : z))
    (h&1 ? -u : u) + (h&2 ? -v : v)
}

func noise(x, y, z) {
    var(X, Y, Z) = [x, y, z].map { .floor & 255 }...
    var (u, v, w) = [x-=X, y-=Y, z-=Z].map { fade(_) }...
    var (AA, AB) = with(p[X]   + Y) {|i| (p[i] + Z, p[i+1] + Z) }
    var (BA, BB) = with(p[X+1] + Y) {|i| (p[i] + Z, p[i+1] + Z) }
    lerp(w, lerp(v, lerp(u, grad(p[AA  ], x  , y  , z  ),
                            grad(p[BA  ], x-1, y  , z  )),
                    lerp(u, grad(p[AB  ], x  , y-1, z  ),
                            grad(p[BB  ], x-1, y-1, z  ))),
            lerp(v, lerp(u, grad(p[AA+1], x  , y  , z-1),
                            grad(p[BA+1], x-1, y  , z-1)),
                    lerp(u, grad(p[AB+1], x  , y-1, z-1),
                            grad(p[BB+1], x-1, y-1, z-1))))
}

var r = noise(3.14, 42, 7)
assert_eq(r, 534843589/3906250000)
say r