Hacker's Delight

5-4. Counting Trailing 0’s

If the number of leading zeros instruction is available, then the best way to count trailing 0’s is, most likely, to convert it to a count leading 0’s problem:

If population count is available, a slightly better method is to form a mask that identifies the trailing 0’s, and count the 1-bits in it [Hay2], such as

Variations exist using other expressions for forming a mask that identifies the trailing zeros of x, such as those given in Section 2-1,“Manipulating Rightmost Bits” on page 11. These methods are also reasonable ...