Less than

The lt instructions, short for less than, check if a number is less than another number. If the first number is less than the second number equal 1 will be pushed on to the stack, otherwise 0 will be pushed on to the stack.

The integer types have separate less than instructions for signed (lt_s) and unsigned (lt_u) numbers.

Try it

(module
  (import "env" "log_bool" (func $log_bool (param i32)))
  (func $main
    ;; load `10` and `2` onto the stack
    i32.const 10
    i32.const 2

    i32.lt_u ;; check if `10` is less than '2'
    call $log_bool ;; log the result
  )
  (start $main)
)

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

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

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

Syntax

wasm

;; load 2 numbers on to the stack
local.get $num
i32.const 2

;; check if $num is less than '2'
i32.lt_u

;; if $num is less than the `2`, `1` will be pushed on to the stack,
;; otherwise `0` will be pushed on to the stack.

Instruction	Binary opcode
`i32.lt_s`	`0x48`
`i32.lt_u`	`0x49`
`i64.lt_s`	`0x53`
`i64.lt_u`	`0x54`
`f32.lt`	`0x5d`
`f64.lt`	`0x63`