index.md

---

title: Count leading zeros
slug: WebAssembly/Reference/Numeric/Count_leading_zeros

---

{{WebAssemblySidebar}}

The clz instructions, short for count leading zeros, are used to count the amount of zeros at the start of the numbers binary representation.

{{EmbedInteractiveExample("pages/wat/clz.html", "tabbed-taller")}}

Syntax

;; load a number onto the stack
i32.const 8388608 ;; 00000000_10000000_00000000_00000000

;; count leading zeros
i32.clz

;; the top item on the stack will now be 8

Instruction	Binary opcode
i32.clz	0x67
i64.clz	0x79