extmul_low_i8x16_s: Wasm SIMD arithmetic instruction

The extmul_low_i8x16_s SIMD arithmetic instruction takes lanes 0–7 of two signed v128 i8x16 value interpretations, multiplies the values in the corresponding lanes, and outputs the result of those operations into an i16x8 value interpretation.

Try it

(module
  (import "console" "log" (func $log (param i32)))
  (func $main
    v128.const i8x16 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3
    v128.const i8x16 4 4 4 4 4 4 4 4 5 5 5 5 5 5 5 5

    i16x8.extmul_low_i8x16_s
    i16x8.extract_lane_s 7
    call $log ;; log the result
  )
  (start $main)
)

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

In the above example, lanes 0–7 of the two i8x16 input values are multiplied together and the products output as an i16x8. Lane 0 of the first input is multiplied by lane 0 of the second input, and the product becomes lane 0 of the output, and so on. As a result, each lane of the output contains the value 8 (2 * 4).

The extmul_low_i8x16_s instruction is a more performant equivalent to passing the results of two extend_low_i8x16_s instructions into a mul instruction.

In other words:

(i16x8.extmul_low_i8x16_s
  (input1)
  (input2)
)

is equivalent to

(i16x8.mul
  (i16x8.extend_low_i8x16_s
    (input1)
  )
  (i16x8.extend_low_i8x16_s
    (input2)
  )
)

Syntax

i16x8.extmul_low_i8x16_s

i16x8.extmul_low_i8x16_s

The i16x8.extmul_low_i8x16_s instruction.

Type

[input1, input2] -> [output]

input1

The first input v128 i8x16 value interpretation.

input2

The second input v128 i8x16 value interpretation.

output

The output v128 i16x8 value interpretation.

Binary encoding

Specifications

• WebAssembly Core Specification