abs: Wasm text instruction

Try it

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

    f32.const -10 ;; load a number onto the stack
    f32.abs ;; calculate the absolute value
    call $log ;; log the result

  )
  (start $main)
)

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

Syntax

value_type.abs

value_type

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

• f32
• f64
• i8x16
• i16x8
• i32x4
• i64x2
• f32x4
• f64x2

abs

The abs 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 abs, the input and output will be basic numeric values such as -3.5 or 3.5.

For a SIMD abs, the input and output will be v128 value interpretations, for example i32x4 4 -8 12 -16.

Binary encoding

Examples

SIMD abs

In this example, we demonstrate running the abs instruction on a SIMD value and outputting one of the resulting lane values.

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 a SIMD i32x4 value, then run i32x4.abs. Finally we extract the value stored in lane 3 of the output SIMD 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 i32)))

  (func $main
    ;; load two SIMD values onto the stack
    v128.const i32x4 -9 -10 -11 -12

    i32x4.abs
    i32x4.extract_lane 3 ;; Extract a value from the result

    call $output
  )

  (start $main)
)

Result

The output is as follows:

The result is 12, because the value stored in lane 3 of the input value is -12, as we are outputting the absolute equivalent.