files/en-us/webassembly/reference/numeric/ctz/index.md
The ctz instructions, short for count trailing zeros, are used to count the amount of zeros at the end of the numbers binary representation.
{{InteractiveExample("Wat Demo: ctz", "tabbed-taller")}}
(module
(func (export "trailing0") (param $num i32) (result i32)
;; load number onto the stack
local.get $num
;; check how many trailing zeros and return the result
i32.ctz
)
)
const url = "{%wasm-url%}";
await WebAssembly.instantiateStreaming(fetch(url), { console }).then(
(result) => {
const trailing0 = result.instance.exports.trailing0;
console.log(
`Trailing zeros: ${trailing0(0b00000000_10000000_00000000_00000000)}`,
);
// Expected output: "Trailing zeros: 23"
},
);
;; load a number onto the stack
i32.const 8388608 ;; 00000000_10000000_00000000_00000000
;; count trailing zeros
i32.ctz
;; the top item on the stack will now be 23
| Instruction | Binary opcode |
|---|---|
i32.ctz | 0x68 |
i64.ctz | 0x7a |