From 2839e35d1c06ca5b6bda1f20ae870f2b2fbbbfb1 Mon Sep 17 00:00:00 2001
From: r00ster91 <r00ster91@proton.me>
Date: Mon, 29 May 2023 01:48:24 +0200
Subject: [PATCH] std.math.isPowerOfTwo: add tests and doc comment and improve
 assert

The assert is changed from `int != 0` to `int > 0` because negative
integers always return `false`.
Python's `math.log2` does the same and errors for 0 or negative integers.
---
 lib/std/math.zig | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/lib/std/math.zig b/lib/std/math.zig
index e60e964747..e62a208d0b 100644
--- a/lib/std/math.zig
+++ b/lib/std/math.zig
@@ -1111,9 +1111,22 @@ pub fn alignCast(comptime alignment: u29, ptr: anytype) AlignCastError!@TypeOf(@
     return @alignCast(alignment, ptr);
 }
 
-pub fn isPowerOfTwo(v: anytype) bool {
-    assert(v != 0);
-    return (v & (v - 1)) == 0;
+/// Asserts `int > 0`.
+pub fn isPowerOfTwo(int: anytype) bool {
+    assert(int > 0);
+    return (int & (int - 1)) == 0;
+}
+
+test isPowerOfTwo {
+    try testing.expect(isPowerOfTwo(@as(u8, 1)));
+    try testing.expect(isPowerOfTwo(2));
+    try testing.expect(!isPowerOfTwo(@as(i16, 3)));
+    try testing.expect(isPowerOfTwo(4));
+    try testing.expect(!isPowerOfTwo(@as(u32, 31)));
+    try testing.expect(isPowerOfTwo(32));
+    try testing.expect(!isPowerOfTwo(@as(i64, 63)));
+    try testing.expect(isPowerOfTwo(128));
+    try testing.expect(isPowerOfTwo(@as(u128, 256)));
 }
 
 /// Aligns the given integer type bit width to a width divisible by 8.