Comparisons in WebAssembly

Tests return an i32 — one for true, zero for false.

(module
  ;; Comparisons return i32: one for true, zero for false. The _s and
  ;; _u suffixes say how to read the sign bit.
  (func (export "is_freezing") (param $temp i32) (result i32)
    (i32.le_s (local.get $temp) (i32.const 0)))

  (func (export "in_range") (param $n i32) (param $lo i32) (param $hi i32)
        (result i32)
    (i32.and
      (i32.ge_s (local.get $n) (local.get $lo))
      (i32.le_s (local.get $n) (local.get $hi))))

  ;; eqz is the one-operand shortcut for "equals zero".
  (func (export "is_empty") (param $count i32) (result i32)
    (i32.eqz (local.get $count))))

How it works

1. i32.le_s compares signed; the result is just an integer.
2. i32.and combines two tests into a range check.
3. i32.eqz is the shorthand for comparing against zero.

Keywords and builtins used here

• export
• func
• i32
• module
• param
• result

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Step 2 of 3 in Numbers, step 5 of 28 in Language basics.

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