Count trailing zeros

The ctz instructions, short for count trailing zeros, are used to count the amount of zeros at the end of the numbers binary representation.

Try it

(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

wasm
;; 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