nearest: Wasm text instruction

Try it

(module
  (import "console" "log" (func $log (param f32)))
  (func $main

    f32.const 2.7 ;; load a number onto the stack
    f32.nearest ;; round to the nearest integer
    call $log ;; log the result

  )
  (start $main)
)

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

Syntax

value_type.nearest

value_type

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

• f32
• f64
• f32x4
• f64x2

nearest

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

Type

[input] -> [output]

input

The input value.

output

The output value.

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

For a SIMD nearest, these will be v128 value interpretations, for example f32x4 3.5 6.0 10.1 40.9.

Binary encoding

Examples

SIMD nearest rounding

In this example, we demonstrate using nearest to round a SIMD value.

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 f32 parameter. We then declare a SIMD f32x4 value and use f32x4.nearest to round all its lanes to the nearest integer. Finally we extract the value stored in lane 3 of the output value using the extract_lane instruction, and output it to the DOM by calling the imported output() function.

(module
  ;; Import output function
  (import "obj" "output" (func $output (param f32)))

  (func $main
    ;; load a SIMD value onto the stack
    v128.const f32x4 400.3 28.5 79.9 80.1

    f32x4.nearest ;; convert lanes to nearest integer
    f32x4.extract_lane 3 ;; Extract a value from the result
    call $output
  )

  (start $main)
)

Result

The output is as follows:

80 is output because it is the nearest whole number to the value in lane 3 of the input value (80.1).