memory.size and memory.grow in WebAssembly

Memory is counted in 64 KiB pages, growable at run time.

(module
  ;; Memory is measured in 64 KiB pages. size reports the current
  ;; count; grow adds pages and returns the old count, or -1.
  (memory 1 4)

  (func (export "pages_now") (result i32)
    memory.size)

  (func (export "add_pages") (param $n i32) (result i32)
    (memory.grow (local.get $n)))

  (func (export "bytes_available") (result i32)
    (i32.mul memory.size (i32.const 65536))))

How it works

(memory 1 4) starts at one page and caps at four.
memory.grow adds pages, returning the old count or -1.
Multiplying memory.size by 65536 turns pages into bytes.

Keywords and builtins used here

export
func
i32
memory
module
param
result

The run, in numbers

Lines: 13
Characters to type: 373
Tokens: 69
Three-star pace: 65 tpm

At the three-star pace of 65 tokens a minute, this run takes about 64 seconds.

Type this snippet

Step 3 of 4 in Memory, step 18 of 28 in Language basics.

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