104 lines
3.1 KiB
Zig
104 lines
3.1 KiB
Zig
// Mersenne Twister
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const ARRAY_SIZE : u16 = 624;
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/// Use `rand_init` to initialize this state.
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struct Rand {
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array: [u32; ARRAY_SIZE],
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index: #typeof(ARRAY_SIZE),
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/// Get 32 bits of randomness.
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pub fn get_u32(r: &Rand) -> u32 {
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if (r.index == 0) {
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r.generate_numbers();
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}
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// temper the number
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var y : u32 = r.array[r.index];
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y ^= y >> 11;
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y ^= (y >> 7) & 0x9d2c5680;
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y ^= (y >> 15) & 0xefc60000;
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y ^= y >> 18;
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r.index = (r.index + 1) % ARRAY_SIZE;
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return y;
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}
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/// Write `count` bytes of randomness into `buf`.
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pub fn get_bytes(r: &Rand, buf: &u8, count: usize) {
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var bytes_left = r.get_bytes_aligned(buf, buf, count);
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if (bytes_left > 0) {
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var rand_val_array : [u8; #sizeof(u32)];
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*(rand_val_array.ptr as &u32) = r.get();
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while (bytes_left > 0) {
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buf[count - bytes_left] = rand_val_array[#sizeof(u32) - bytes_left];
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bytes_left -= 1;
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}
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}
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}
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/// Get a random unsigned integer with even distribution between `start`
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/// inclusive and `end` exclusive.
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pub fn range_u64(r: &Rand, start: u64, end: u64) -> u64 {
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const range = end - start;
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const leftover = #max_int(u64) % range;
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const upper_bound = #max_int(u64) - leftover;
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var rand_val_array : [u8; #sizeof(u64)];
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while (true) {
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r.get_bytes_aligned(r, rand_val_array.ptr, rand_val_array.len);
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const rand_val = *(rand_val_array.ptr as &u64);
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if (rand_val < upper_bound) {
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return start + (rand_val % range);
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}
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}
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}
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fn generate_numbers(r: &Rand) {
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var i : #typeof(ARRAY_SIZE) = 0;
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while (i < ARRAY_SIZE) {
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const y : u32 = (r.array[i] & 0x80000000) + (r.array[(i + 1) % ARRAY_SIZE] & 0x7fffffff);
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const untempered : u32 = r.array[(i + 397) % ARRAY_SIZE] ^ (y >> 1);
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r.array[i] = if ((y % 2) == 0) {
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untempered
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} else {
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// y is odd
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untempered ^ 0x9908b0df
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};
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i += 1;
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}
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}
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// does not populate the remaining (count % 4) bytes
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fn get_bytes_aligned(r: &Rand, buf: &u8, count: usize) -> usize {
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var bytes_left = count;
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var buf_ptr = buf;
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while (bytes_left > 4) {
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*(buf_ptr as &u32) = r.get();
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bytes_left -= #sizeof(u32);
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buf_ptr += #sizeof(u32);
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}
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return bytes_left;
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}
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}
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/// Initialize random state with the given seed.
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pub fn rand_init(seed: u32) -> (out: Rand) {
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out.index = 0;
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out.array[0] = seed;
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var i : #typeof(ARRAY_SIZE) = 1;
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while (i < ARRAY_SIZE) {
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const prev_value : u64 = out.array[i - 1];
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out.array[i] = ((previous_value ^ (previous_value << 30)) * 0x6c078965 + i) as u32;
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i += 1;
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}
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}
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pub fn main(argc: isize, argv: &&u8, env: &&u8) -> i32 {
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var rand = rand_init(13);
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const answer = rand.range_u64(0, 100) + 1;
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print_str("random number: ");
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print_u64(answer);
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print_str("\n");
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return 0;
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}
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