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std.rand: Accept ints with >64 bits in uintLessThanBiased

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This commit is contained in:
e4m2 2023-08-15 11:53:48 +02:00
parent 9135115573
commit 6f129c9912
1 changed files with 3 additions and 10 deletions
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13
lib/std/rand.zig
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@ -121,14 +121,8 @@ pub const Random = struct {
/// The results of this function may be biased.
pub fn uintLessThanBiased(r: Random, comptime T: type, less_than: T) T {
comptime assert(@typeInfo(T).Int.signedness == .unsigned);
const bits = @typeInfo(T).Int.bits;
comptime assert(bits <= 64); // TODO: workaround: LLVM ERROR: Unsupported library call operation!
assert(0 < less_than);
if (bits <= 32) {
return @as(T, @intCast(limitRangeBiased(u32, r.int(u32), less_than)));
} else {
return @as(T, @intCast(limitRangeBiased(u64, r.int(u64), less_than)));
}
return limitRangeBiased(T, r.int(T), less_than);
}
/// Returns an evenly distributed random unsigned integer `0 <= i < less_than`.
@ -438,13 +432,12 @@ pub const Random = struct {
pub fn limitRangeBiased(comptime T: type, random_int: T, less_than: T) T {
comptime assert(@typeInfo(T).Int.signedness == .unsigned);
const bits = @typeInfo(T).Int.bits;
const T2 = std.meta.Int(.unsigned, bits * 2);
// adapted from:
// http://www.pcg-random.org/posts/bounded-rands.html
// "Integer Multiplication (Biased)"
var m: T2 = @as(T2, random_int) * @as(T2, less_than);
return @as(T, @intCast(m >> bits));
const m = math.mulWide(T, random_int, less_than);
return @intCast(m >> bits);
}
// Generator to extend 64-bit seed values into longer sequences.