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| author | Niles Salter <Validark@pm.me> | 2023-06-20 17:32:07 -0600 |
|---|---|---|
| committer | Andrew Kelley <andrew@ziglang.org> | 2023-06-22 01:57:28 -0700 |
| commit | ff5850183eee854fdfe0d3f7b7242b9ff56c2116 (patch) | |
| tree | 715ed346487b0f221f92e26280ea5e5b52a9254a /lib/std/priority_dequeue.zig | |
| parent | 991e00c2702b31dffb7b5ada26c7b19a552502a7 (diff) | |
| download | zig-ff5850183eee854fdfe0d3f7b7242b9ff56c2116.tar.gz zig-ff5850183eee854fdfe0d3f7b7242b9ff56c2116.zip | |
[priority_deque] simplify & optimize isMinLayer
LLVM has trouble compiling the old implementation, (presumably) because `leading_zeros` is thought to be a `u7` rather than a `u6`, which means `63 - clz` is not equivalent to `63 ^ clz`, which means it can't deduce that the final condition can simply be flipped. (I am assuming `usize` is a `u64` here for ease of understanding, but it's the same for any power of 2)
https://zig.godbolt.org/z/Pbj4P7ob3
The new version is slightly better too because `isMinLayer(maxInt(usize))` is now well-defined behavior.
Diffstat (limited to 'lib/std/priority_dequeue.zig')
| -rw-r--r-- | lib/std/priority_dequeue.zig | 4 |
1 files changed, 1 insertions, 3 deletions
diff --git a/lib/std/priority_dequeue.zig b/lib/std/priority_dequeue.zig index 05e3d7e58b..510c3dd1cf 100644 --- a/lib/std/priority_dequeue.zig +++ b/lib/std/priority_dequeue.zig @@ -69,9 +69,7 @@ pub fn PriorityDequeue(comptime T: type, comptime Context: type, comptime compar // The first element is on a min layer; // next two are on a max layer; // next four are on a min layer, and so on. - const leading_zeros = @clz(index + 1); - const highest_set_bit = @bitSizeOf(usize) - 1 - leading_zeros; - return (highest_set_bit & 1) == 0; + return 1 == @clz(index +% 1) & 1; } fn nextIsMinLayer(self: Self) bool { |