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
• v128 interpretations:
  • 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, which will be a floating point number.

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. Each lane of the output pushed to the stack will be equal to the corresponding lane of the input value rounded to the nearest whole number.

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).