lt_s: Wasm text instruction

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.lt_s ;; check if 10 is less than 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.lt_s

value_type

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

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

lt_s

The lt_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. If the first input is less than the second input, 1 will be pushed on to the stack, otherwise 0 will be pushed on to the stack. The output values are integers.

For a non-SIMD lt_s, the inputs will be basic numeric values such as 3 or 12.

For a SIMD lt_s, the inputs will be v128 value interpretations, for example i32x4 2 30 86 120.

Binary encoding

Examples

SIMD lt_s example

In this example, we demonstrate using lt_s to test whether one SIMD lane value is less than 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 the second using i32x4.lt_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 the second
    i32x4.lt_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 the value stored in lane 3 of the second input value.

See also

• lt
• lt_u