The mul numeric instruction, short for multiplication, is used for multiplying one number by another number, similar to the * operator in other languages.

(module
  (import "console" "log" (func $log (param i32)))
  (func $main
    ;; load `10` and `3` onto the stack
    i32.const 10
    i32.const 3

    i32.mul ;; multiply one number by the other
    call $log ;; log the result
  )
  (start $main)
)

const url = "{%wasm-url%}";
await WebAssembly.instantiateStreaming(fetch(url), { console });

Syntax

value_type.mul

• value_type

  • : The type of value the instruction is being run on. The following types support mul:

    • i32

    • i64

    • f32

    • f64

    • v128 interpretations:

      • i16x8

      • i32x4

      • i64x2

      • f32x4

      • f64x2

  mul

  • : The mul instruction. Must always be included after the value_type and a period (.).

Type

[input1, input2] -> [output]

• input1

  • : The first input value.

  input2

  • : The second input value.

  output

  • : The product of the two input values.

For a non-SIMD mul, these will be basic numeric values such as 3 or 3.5.

For a SIMD mul, these will be v128 value interpretations, for example f32x4 0x9 0xa 0xb 0xc. Each lane of the output pushed to the stack is the product of the two inputs’ corresponding lane values being multiplied together.

Binary encoding

InstructionBinary formatExample text => binaryi32.mul0x6ci32.mul => 0x6ci64.mul0x7ei64.mul => 0x7ef32.mul0x94f32.mul => 0x94f64.mul0xa2f64.mul => 0xa2i16x8.mul0xfd 149:u32i16x8.mul => 0xfd 0x95 0x01i32x4.mul0xfd 181:u32i32x4.mul => 0xfd 0xb5 0x01i64x2.mul0xfd 213:u32i64x2.mul => 0xfd 0xd5 0x01f32x4.mul0xfd 230:u32f32x4.mul => 0xfd 0xe6 0x01f64x2.mul0xfd 242:u32f64x2.mul => 0xfd 0xf2 0x01

Examples

SIMD multiplication

In this example, we demonstrate multiplying one SIMD value by another and outputting one of the lane values of the resulting product.

JavaScript

In our script, we grab a reference to a <p> element that we will output our result to, then define an object for import into Wasm containing a single function that writes a value to the output <p>. We then compile and instantiate our Wasm module using the WebAssembly.instantiateStreaming() method, importing the object in the process.

<p></p>

const outputElem = document.querySelector("p");

const obj = {
  output(val) {
    outputElem.textContent += val;
  },
};

WebAssembly.instantiateStreaming(fetch("{%wasm-url%}"), {
  obj,
});

Wasm

In our Wasm module, we first import the JavaScript output() function, making sure to declare that it has an i32 parameter. We then declare two SIMD i16x8 values, then multiply the first by the second using i16x8.mul. Finally we extract the value stored in lane 7 of the output value using the extract_lane_s instruction, and output it to the DOM by calling the imported output() function.

(module
  ;; Import output function
  (import "obj" "output" (func $output (param i32)))

  (func $main
    ;; load two SIMD values onto the stack
    v128.const i16x8 20 12 15 2 400 2 1 12
    v128.const i16x8 18 34 3 5 9 20 21 9

    i16x8.mul ;; multiply the two values
    i16x8.extract_lane_s 7 ;; Extract a value from the result

    call $output
  )

  (start $main)
)

Result

The output is as follows:

The result is 108, because the value stored in lane 3 of output value is the result of 12 * 9.

Specifications

Browser compatibility