Conversions in WebAssembly

destination.op_source, signedness included — nothing is implicit.

(module
  ;; Conversions are all spelled out: destination.op_source, with
  ;; signedness where it matters. Nothing converts implicitly.
  (func (export "ratio") (param $part i32) (param $whole i32)
        (result f64)
    (f64.div
      (f64.convert_i32_s (local.get $part))
      (f64.convert_i32_s (local.get $whole))))

  ;; trunc drops the fraction and traps if it cannot fit.
  (func (export "whole_meters") (param $km f64) (result i32)
    (i32.trunc_f64_s (f64.mul (local.get $km) (f64.const 1000))))

  (func (export "shrink") (param $precise f64) (result f32)
    (f32.demote_f64 (local.get $precise))))

How it works

1. f64.convert_i32_s reads an integer into float land.
2. i32.trunc_f64_s drops the fraction and traps on overflow.
3. f32.demote_f64 narrows a float; promote would widen it.

Keywords and builtins used here

• export
• f32
• f64
• func
• i32
• module
• param
• result

The run, in numbers

Lines

15

Characters to type

570

Tokens

103

Three-star pace

60 tpm

At the three-star pace of 60 tokens a minute, this run takes about 103 seconds.

Type this snippet

Step 2 of 3 in Wider types, step 24 of 28 in Language basics.

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Conversions in other languages

• Go