swizzle: Wasm SIMD conversion instruction

The swizzle SIMD conversion instruction returns a new v128 value with its lane values selected from an input v128 value, determined by indices provided in a second input v128.

Try it

(module
  (import "console" "log" (func $log (param i32)))
  (func $main
    v128.const i8x16 10 23 56 15 25 29 92 45 36 4 78 12 34 25 72 82
    v128.const i8x16 0 2 5 7 3 5 9 2 4 6 1 7 0 3 5 1
    i8x16.swizzle

    i8x16.extract_lane_u 6
    call $log ;; log the result
  )
  (start $main)
)

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

In the above example, we extract and log the value at index position 6 of the swizzle instruction output value. This will be 4, because the swizzle instruction has selected the value at index position 9 of the input value to be put at index position 6 of the output value.

Syntax

value_type.swizzle

value_type

The type of value the instruction is being run on. The following v128 value interpretations support swizzle:

• i8x16

swizzle

The swizzle instruction. Must always be included after the value_type and a period (.).

Type

[input, indices] -> [output]

input

The input v128 i8x16 value interpretation.

indices

The v128 value containing the indices you want to use to select which values should be taken from the input value and included in the output. In each case, the index number represents the index position to take from the input value, and the position of the index represents the position it should appear in the output value.

These values must be between 0 and 15, inclusive. For indices outside this range, the resulting lanes will be initialized to 0.

output

The output v128 value interpretation.

Binary encoding

Specifications

• WebAssembly Core Specification