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std.math.big.int: add log2

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hemisputnik 2026-02-28 00:46:05 +02:00
parent 99229ceb55
commit 925f82da09
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5
lib/std/math/big/int.zig
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@ -2670,6 +2670,11 @@ pub const Const = struct {
}
return @min(result, bits);
}
/// Calculate the base 2 logarithm, rounded down.
pub fn log2(a: Const) Limb {
return a.limbs.len * @bitSizeOf(Limb) - 1 - @clz(a.limbs[a.limbs.len - 1]);
}
};
/// An arbitrary-precision big integer along with an allocator which manages the memory.

17
lib/std/math/big/int_test.zig
View file

@ -4072,3 +4072,20 @@ test "ctz" {
try testing.expectEqual(0, limb_max_squared.ctz(@bitSizeOf(Limb) * 2));
try testing.expectEqual(0, limb_max_squared.ctz(@bitSizeOf(Limb) * 2 + 1));
}
test "log2" {
var a = try Managed.init(testing.allocator);
defer a.deinit();
try a.setString(2, "1");
try testing.expectEqual(0, a.toConst().log2());
try a.setString(2, "1111011");
try testing.expectEqual(6, a.toConst().log2());
try a.setString(2, "10100111011101010");
try testing.expectEqual(16, a.toConst().log2());
try a.setString(16, "a22d71c87a9ce406da4f5895f9f3cc3d603192baf6c8a2b5c32649d0465bf188fe799b3618085e49d71bdaec01");
try testing.expectEqual(359, a.toConst().log2());
}