Commit c0baed4a3e8cf710a90f9909fdf383e3c1c52682 | zig

1 files changed, 8 insertions(+), 14 deletions(-)

lib/std/rand.zig+8-14

...	...	@@ -136,22 +136,16 @@ pub const Random = struct {
136	136	pub fn uintLessThan(r: Random, comptime T: type, less_than: T) T {
137	137	comptime assert(@typeInfo(T).Int.signedness == .unsigned);
138	138	const bits = @typeInfo(T).Int.bits;
139		comptime assert(bits <= 64); // TODO: workaround: LLVM ERROR: Unsupported library call operation!
140	139	assert(0 < less_than);
141		// Small is typically u32
142		const small_bits = @divTrunc(bits + 31, 32) * 32;
143		const Small = std.meta.Int(.unsigned, small_bits);
144		// Large is typically u64
145		const Large = std.meta.Int(.unsigned, small_bits * 2);
146	140
147	141	// adapted from:
148	142	// http://www.pcg-random.org/posts/bounded-rands.html
149	143	// "Lemire's (with an extra tweak from me)"
150		var x: Small = r.int(Small);
151		var m: Large = @as(Large, x) * @as(Large, less_than);
152		var l: Small = @as(Small, @truncate(m));
	144	var x = r.int(T);
	145	var m = math.mulWide(T, x, less_than);
	146	var l: T = @truncate(m);
153	147	if (l < less_than) {
154		var t: Small = -%less_than;
	148	var t = -%less_than;
155	149
156	150	if (t >= less_than) {
157	151	t -= less_than;
...	...	@@ -160,12 +154,12 @@ pub const Random = struct {
160	154	}
161	155	}
162	156	while (l < t) {
163		x = r.int(Small);
164		m = @as(Large, x) * @as(Large, less_than);
165		l = @as(Small, @truncate(m));
	157	x = r.int(T);
	158	m = math.mulWide(T, x, less_than);
	159	l = @truncate(m);
166	160	}
167	161	}
168		return @as(T, @intCast(m >> small_bits));
	162	return @intCast(m >> bits);
169	163	}
170	164
171	165	/// Constant-time implementation off `uintAtMost`.