le_s: Wasm numeric instruction

The le_s numeric instruction, short for less or equal signed, checks if a signed integer is less than or equal to another signed integer.

There are other le instructions available:

• le_u for comparing unsigned integers.
• le for comparing floating point numbers.

Try it

(module
  (import "env" "log_bool" (func $log_bool (param i32)))
  (func $main
    ;; load 10 and 3 onto the stack
    i32.const 10
    i32.const 3

    i32.le_s ;; check if 10 is less than or equal to 3
    call $log_bool ;; log the result
  )
  (start $main)
)

const url = "{%wasm-url%}";

function log_bool(value) {
  console.log(Boolean(value));
  // Expected output: true
}

await WebAssembly.instantiateStreaming(fetch(url), {
  env: { log_bool },
});

Syntax

value_type.le_s

value_type

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

• i32
• i64
• v128 interpretations:
  • i8x16
  • i16x8
  • i32x4
  • i64x2

le_s

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

Type

[input1, input2] -> [output]

input1

The first input value.

input2

The second input value.

output

The output value, which will be an integer type.

For a non-SIMD le_s, the inputs will be basic numeric values such as 3 or 12. If the first input is less than or equal to the second input, 1 will be pushed on to the stack as an output, otherwise 0 will be pushed on to the stack.

For a SIMD le_s, the inputs will be v128 value interpretations, for example i32x4 2 30 86 120. Each lane of the output pushed to the stack is a 1 or 0 indicating whether the corresponding lane of the first input value is less than or equal to the corresponding lane of the second input value.

Binary encoding

Examples

SIMD le_s example

In this example, we demonstrate using le_s to test whether one SIMD lane value is less than or equal to the same lane value in another 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 i32 parameter. We then declare two SIMD i32x4 values, then check whether the first one's lane values are less than or equal to the second using i32x4.le_s. 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 i32)))

  (func $main
    ;; load two SIMD values onto the stack
    v128.const i32x4 20 12 15 102
    v128.const i32x4 20 12 15 100

    ;; check whether the first value is less than or equal to the second
    i32x4.le_s
    i32x4.extract_lane 3 ;; Extract a value from the result

    call $output
  )

  (start $main)
)

Result

The output is as follows:

The result is 0 because the value stored in lane 3 of the first input value is not less than or equal to the value stored in lane 3 of the second input value.

Specifications

• WebAssembly Core Specification

See also

• le
• le_u