The problem with using the quirky update is that it's, well, quirky.  It's not guaranteed to work.  Here is a method that uses guaranteed methods and performs only slightly slower on this sample data.

;
WITH CTETally AS
(
    SELECT n
    FROM (VALUES(1), (1), (1), (1), (1), (1)) n(n)
)
, bits AS
(
    SELECT TOP(31) POWER(CAST(2 AS BIGINT), ROW_NUMBER() OVER(ORDER BY @@VERSION) - 1) AS bitmask
    FROM CTETally A
    CROSS JOIN CTETally AS b
)
, bitmasks AS
(
    SELECT s.[Date], s.BitValue & b.bitmask AS BitValues
    FROM #Sample s
    INNER JOIN bits b
        ON s.BitValue & b.bitmask = b.bitmask
    GROUP BY s.[Date], s.BitValue & b.bitmask
)
SELECT [Date], SUM(BitValues)
FROM bitmasks
GROUP BY [Date]
ORDER BY [Date]


I haven't tested this on a large dataset.

Drew