The ctz numeric instruction, short for count trailing zeros, is used to count the amount of zeros at the end of the numbers binary representation.

(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"
  },
);

Syntax

;; 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

InstructionBinary opcodei32.ctz0x68i64.ctz0x7a

Specifications

Browser compatibility