zig/std/rand.zig
Andrew Kelley 987768778a bit shifting safety
* add u3, u4, u5, u6, u7 and i3, i4, i5, i6, i7
 * shift operations shift amount parameter type is
   integer with log2 bit width of other param
   - This enforces not violating undefined behavior on
     shift amount >= bit width with the type system
 * clean up math.log, math.ln, math.log2, math.log10

closes #403
2017-08-19 01:43:43 -04:00

239 lines
7.3 KiB
Zig

const assert = @import("debug.zig").assert;
const rand_test = @import("rand_test.zig");
const mem = @import("mem.zig");
const math = @import("math/index.zig");
pub const MT19937_32 = MersenneTwister(
u32, 624, 397, 31,
0x9908B0DF,
11, 0xFFFFFFFF,
7, 0x9D2C5680,
15, 0xEFC60000,
18, 1812433253);
pub const MT19937_64 = MersenneTwister(
u64, 312, 156, 31,
0xB5026F5AA96619E9,
29, 0x5555555555555555,
17, 0x71D67FFFEDA60000,
37, 0xFFF7EEE000000000,
43, 6364136223846793005);
/// Use `init` to initialize this state.
pub const Rand = struct {
const Rng = if (@sizeOf(usize) >= 8) MT19937_64 else MT19937_32;
rng: Rng,
/// Initialize random state with the given seed.
pub fn init(seed: usize) -> Rand {
Rand {
.rng = Rng.init(seed),
}
}
/// Get an integer or boolean with random bits.
pub fn scalar(r: &Rand, comptime T: type) -> T {
if (T == usize) {
return r.rng.get();
} else if (T == bool) {
return (r.rng.get() & 0b1) == 0;
} else {
var result: [@sizeOf(T)]u8 = undefined;
r.fillBytes(result[0..]);
return mem.readInt(result, T, false);
}
}
/// Fill `buf` with randomness.
pub fn fillBytes(r: &Rand, buf: []u8) {
var bytes_left = buf.len;
while (bytes_left >= @sizeOf(usize)) {
mem.writeInt(buf[buf.len - bytes_left..], r.rng.get(), false);
bytes_left -= @sizeOf(usize);
}
if (bytes_left > 0) {
var rand_val_array: [@sizeOf(usize)]u8 = undefined;
mem.writeInt(rand_val_array[0..], r.rng.get(), false);
while (bytes_left > 0) {
buf[buf.len - bytes_left] = rand_val_array[@sizeOf(usize) - bytes_left];
bytes_left -= 1;
}
}
}
/// Get a random unsigned integer with even distribution between `start`
/// inclusive and `end` exclusive.
pub fn range(r: &Rand, comptime T: type, start: T, end: T) -> T {
assert(start <= end);
if (T.is_signed) {
const uint = @IntType(false, T.bit_count);
if (start >= 0 and end >= 0) {
return T(r.range(uint, uint(start), uint(end)));
} else if (start < 0 and end < 0) {
// Can't overflow because the range is over signed ints
return %%math.negateCast(r.range(uint, math.absCast(end), math.absCast(start)) + 1);
} else if (start < 0 and end >= 0) {
const end_uint = uint(end);
const total_range = math.absCast(start) + end_uint;
const value = r.range(uint, 0, total_range);
const result = if (value < end_uint) {
T(value)
} else if (value == end_uint) {
start
} else {
// Can't overflow because the range is over signed ints
%%math.negateCast(value - end_uint)
};
return result;
} else {
unreachable;
}
} else {
const total_range = end - start;
const leftover = @maxValue(T) % total_range;
const upper_bound = @maxValue(T) - leftover;
var rand_val_array: [@sizeOf(T)]u8 = undefined;
while (true) {
r.fillBytes(rand_val_array[0..]);
const rand_val = mem.readInt(rand_val_array, T, false);
if (rand_val < upper_bound) {
return start + (rand_val % total_range);
}
}
}
}
/// Get a floating point value in the range 0.0..1.0.
pub fn float(r: &Rand, comptime T: type) -> T {
// TODO Implement this way instead:
// const int = @int_type(false, @sizeOf(T) * 8);
// const mask = ((1 << @float_mantissa_bit_count(T)) - 1);
// const rand_bits = r.rng.scalar(int) & mask;
// return @float_compose(T, false, 0, rand_bits) - 1.0
const int_type = @IntType(false, @sizeOf(T) * 8);
const precision = if (T == f32) {
16777216
} else if (T == f64) {
9007199254740992
} else {
@compileError("unknown floating point type")
};
return T(r.range(int_type, 0, precision)) / T(precision);
}
};
fn MersenneTwister(
comptime int: type, comptime n: usize, comptime m: usize, comptime r: int,
comptime a: int,
comptime u: math.Log2Int(int), comptime d: int,
comptime s: math.Log2Int(int), comptime b: int,
comptime t: math.Log2Int(int), comptime c: int,
comptime l: math.Log2Int(int), comptime f: int) -> type
{
struct {
const Self = this;
array: [n]int,
index: usize,
pub fn init(seed: int) -> Self {
var mt = Self {
.array = undefined,
.index = n,
};
var prev_value = seed;
mt.array[0] = prev_value;
var i: usize = 1;
while (i < n) : (i += 1) {
prev_value = int(i) +% f *% (prev_value ^ (prev_value >> (int.bit_count - 2)));
mt.array[i] = prev_value;
}
return mt;
}
pub fn get(mt: &Self) -> int {
const mag01 = []int{0, a};
const LM: int = (1 << r) - 1;
const UM = ~LM;
if (mt.index >= n) {
var i: usize = 0;
while (i < n - m) : (i += 1) {
const x = (mt.array[i] & UM) | (mt.array[i + 1] & LM);
mt.array[i] = mt.array[i + m] ^ (x >> 1) ^ mag01[x & 0x1];
}
while (i < n - 1) : (i += 1) {
const x = (mt.array[i] & UM) | (mt.array[i + 1] & LM);
mt.array[i] = mt.array[i + m - n] ^ (x >> 1) ^ mag01[x & 0x1];
}
const x = (mt.array[i] & UM) | (mt.array[0] & LM);
mt.array[i] = mt.array[m - 1] ^ (x >> 1) ^ mag01[x & 0x1];
mt.index = 0;
}
var x = mt.array[mt.index];
mt.index += 1;
x ^= ((x >> u) & d);
x ^= ((x << s) & b);
x ^= ((x << t) & c);
x ^= (x >> l);
return x;
}
}
}
test "rand float 32" {
var r = Rand.init(42);
var i: usize = 0;
while (i < 1000) : (i += 1) {
const val = r.float(f32);
assert(val >= 0.0);
assert(val < 1.0);
}
}
test "rand.MT19937_64" {
var rng = MT19937_64.init(rand_test.mt64_seed);
for (rand_test.mt64_data) |value| {
assert(value == rng.get());
}
}
test "rand.MT19937_32" {
var rng = MT19937_32.init(rand_test.mt32_seed);
for (rand_test.mt32_data) |value| {
assert(value == rng.get());
}
}
test "rand.Rand.range" {
var r = Rand.init(42);
testRange(&r, -4, 3);
testRange(&r, -4, -1);
testRange(&r, 10, 14);
}
fn testRange(r: &Rand, start: i32, end: i32) {
const count = usize(end - start);
var values_buffer = []bool{false} ** 20;
const values = values_buffer[0..count];
var i: usize = 0;
while (i < count) {
const value = r.range(i32, start, end);
const index = usize(value - start);
if (!values[index]) {
i += 1;
values[index] = true;
}
}
}