Locals in WebAssembly

Declared up front, zero to start, moved with get and set.

(module
  ;; Locals are declared up front, zero-initialized, and read and
  ;; written with local.get and local.set.
  (func (export "swap_diff") (param $a i32) (param $b i32) (result i32)
    (local $high i32)
    (local $low i32)
    (local.set $high (local.get $a))
    (local.set $low (local.get $b))
    (if (i32.lt_s (local.get $high) (local.get $low))
      (then
        (local.set $high (local.get $b))
        (local.set $low (local.get $a))))
    (i32.sub (local.get $high) (local.get $low))))

How it works

1. (local $high i32) reserves a slot; locals follow the params.
2. local.set pops the stack into the slot; local.get pushes a copy.
3. The if swaps the two slots when the inputs arrive out of order.

Keywords and builtins used here

• export
• func
• i32
• if
• local
• module
• param
• result
• then

The run, in numbers

Lines

13

Characters to type

452

Tokens

98

Three-star pace

65 tpm

At the three-star pace of 65 tokens a minute, this run takes about 90 seconds.

Type this snippet

Step 1 of 3 in Locals & the stack, step 7 of 28 in Language basics.

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