Add math/rand.odin

1 files changed, 60 insertions, 0 deletions

diff --git a/core/math/rand.odin b/core/math/rand.odin
new file mode 100644
index 000000000..4862ad496
--- /dev/null
+++ b/core/math/rand.odin
@@ -0,0 +1,60 @@
+Rand :: struct {
+	state: u64,
+	inc:   u64,
+}
+
+init :: proc(r: ^Rand, seed: u64 = 8675309) {
+	r.state = 0;
+	r.inc = (seed << 1) | 1;
+	_random(r);
+	r.state += seed;
+	_random(r);
+}
+
+_random :: proc(r: ^Rand) -> u32 {
+	old_state := r.state;
+	r.state = old_state * 6364136223846793005 + (r.inc|1);
+	xor_shifted := u32(((old_state>>18) ~ old_state) >> 27);
+	rot := u32(old_state >> 59);
+	return (xor_shifted >> rot) | (xor_shifted << ((-rot) & 31));
+}
+
+uint32 :: proc(r: ^Rand) -> u32 { return _random(r); }
+
+uint64 :: proc(r: ^Rand) -> u64 {
+	a := u64(_random(r));
+	b := u64(_random(r));
+	return (a<<32) | b;
+}
+
+int31 :: proc(r: ^Rand) -> i32 { return i32(uint32(r) << 1 >> 1); }
+int63 :: proc(r: ^Rand) -> i64 { return i64(uint64(r) << 1 >> 1); }
+
+int31_max :: proc(r: ^Rand, n: i32) -> i32 {
+	if n <= 0 do panic("Invalid argument to int31_max");
+	if n&(n-1) == 0 {
+		return int31(r) & (n-1);
+	}
+	max := i32((1<<31) - 1 - (1<<31)&u32(n));
+	v := int31(r);
+	for v > max {
+		v = int31(r);
+	}
+	return v % n;
+}
+
+int63_max :: proc(r: ^Rand, n: i64) -> i64 {
+	if n <= 0 do panic("Invalid argument to int63_max");
+	if n&(n-1) == 0 {
+		return int63(r) & (n-1);
+	}
+	max := i64((1<<63) - 1 - (1<<63)&u64(n));
+	v := int63(r);
+	for v > max {
+		v = int63(r);
+	}
+	return v % n;
+}
+
+float64 :: proc(r: ^Rand) -> f64 { return f64(int63_max(r, 1<<53)) / (1 << 53); }
+float32 :: proc(r: ^Rand) -> f32 { return f32(float64(r)); }