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| 1 | // Mersenne Twister |
| 2 | const ARRAY_SIZE : u16 = 624; |
| 3 | |
| 4 | /// Use `rand_init` to initialize this state. |
| 5 | pub struct Rand { |
| 6 | array: [u32; ARRAY_SIZE], |
| 7 | index: #typeof(ARRAY_SIZE), |
| 8 | |
| 9 | /// Get 32 bits of randomness. |
| 10 | pub fn get_u32(r: &Rand) -> u32 { |
| 11 | if (r.index == 0) { |
| 12 | r.generate_numbers(); |
| 13 | } |
| 14 | |
| 15 | // temper the number |
| 16 | var y : u32 = r.array[r.index]; |
| 17 | y ^= y >> 11; |
| 18 | y ^= (y >> 7) & 0x9d2c5680; |
| 19 | y ^= (y >> 15) & 0xefc60000; |
| 20 | y ^= y >> 18; |
| 21 | |
| 22 | r.index = (r.index + 1) % ARRAY_SIZE; |
| 23 | return y; |
| 24 | } |
| 25 | |
| 26 | /// Write `count` bytes of randomness into `buf`. |
| 27 | pub fn get_bytes(r: &Rand, buf: &u8, count: usize) { |
| 28 | var bytes_left = r.get_bytes_aligned(buf, buf, count); |
| 29 | if (bytes_left > 0) { |
| 30 | var rand_val_array : [u8; #sizeof(u32)]; |
| 31 | *(rand_val_array.ptr as &u32) = r.get(); |
| 32 | while (bytes_left > 0) { |
| 33 | buf[count - bytes_left] = rand_val_array[#sizeof(u32) - bytes_left]; |
| 34 | bytes_left -= 1; |
| 35 | } |
| 36 | } |
| 37 | } |
| 38 | |
| 39 | /// Get a random unsigned integer with even distribution between `start` |
| 40 | /// inclusive and `end` exclusive. |
| 41 | pub fn range_u64(r: &Rand, start: u64, end: u64) -> u64 { |
| 42 | const range = end - start; |
| 43 | const leftover = #max_int(u64) % range; |
| 44 | const upper_bound = #max_int(u64) - leftover; |
| 45 | var rand_val_array : [u8; #sizeof(u64)]; |
| 46 | |
| 47 | while (true) { |
| 48 | r.get_bytes_aligned(r, rand_val_array.ptr, rand_val_array.len); |
| 49 | const rand_val = *(rand_val_array.ptr as &u64); |
| 50 | if (rand_val < upper_bound) { |
| 51 | return start + (rand_val % range); |
| 52 | } |
| 53 | } |
| 54 | } |
| 55 | |
| 56 | fn generate_numbers(r: &Rand) { |
| 57 | var i : #typeof(ARRAY_SIZE) = 0; |
| 58 | while (i < ARRAY_SIZE) { |
| 59 | const y : u32 = (r.array[i] & 0x80000000) + (r.array[(i + 1) % ARRAY_SIZE] & 0x7fffffff); |
| 60 | const untempered : u32 = r.array[(i + 397) % ARRAY_SIZE] ^ (y >> 1); |
| 61 | r.array[i] = if ((y % 2) == 0) { |
| 62 | untempered |
| 63 | } else { |
| 64 | // y is odd |
| 65 | untempered ^ 0x9908b0df |
| 66 | }; |
| 67 | i += 1; |
| 68 | } |
| 69 | } |
| 70 | |
| 71 | // does not populate the remaining (count % 4) bytes |
| 72 | fn get_bytes_aligned(r: &Rand, buf: &u8, count: usize) -> usize { |
| 73 | var bytes_left = count; |
| 74 | var buf_ptr = buf; |
| 75 | while (bytes_left > 4) { |
| 76 | *(buf_ptr as &u32) = r.get(); |
| 77 | bytes_left -= #sizeof(u32); |
| 78 | buf_ptr += #sizeof(u32); |
| 79 | } |
| 80 | return bytes_left; |
| 81 | } |
| 82 | } |
| 83 | |
| 84 | /// Initialize random state with the given seed. |
| 85 | pub fn rand_init(seed: u32) -> (out: Rand) { |
| 86 | out.index = 0; |
| 87 | out.array[0] = seed; |
| 88 | var i : #typeof(ARRAY_SIZE) = 1; |
| 89 | while (i < ARRAY_SIZE) { |
| 90 | const prev_value : u64 = out.array[i - 1]; |
| 91 | out.array[i] = ((previous_value ^ (previous_value << 30)) * 0x6c078965 + i) as u32; |
| 92 | i += 1; |
| 93 | } |
| 94 | } |
| 95 | |
| 96 | pub fn main(argc: isize, argv: &&u8, env: &&u8) -> i32 { |
| 97 | var rand = rand_init(13); |
| 98 | const answer = rand.range_u64(0, 100) + 1; |
| 99 | print_str("random number: "); |
| 100 | print_u64(answer); |
| 101 | print_str("\n"); |
| 102 | return 0; |
| 103 | } |
Andrew Kelley <andrew@ziglang.org> 2016-01-03 00:30:41-07:00