Type System

WebAssembly has a simple but powerful type system with four value types and SIMD type support.

Value Types

Type	Size	Description	Range
i32	32 bit	Signed integer	-2^31 to 2^31-1
i64	64 bit	Signed integer	-2^63 to 2^63-1
f32	32 bit	IEEE 754 floating point	~6-7 digit precision
f64	64 bit	IEEE 754 floating point	~15-16 digit precision

Integer Types

Signed vs Unsigned

;; Signed (i32, i64) — two's complement
(func (export "signed_div") (param i32 i32) (result i32)
  local.get 0
  local.get 1
  i32.div_s)      ;; Signed division

(func (export "unsigned_div") (param i32 i32) (result i32)
  local.get 0
  local.get 1
  i32.div_u)      ;; Unsigned division

SIMD Types

WebAssembly SIMD provides 128-bit vector operations:

Type	Size	Description
v128	128 bit	SIMD vector

SIMD Instructions

(module
  (func (export "add_i8x16") (param v128 v128) (result v128)
    local.get 0
    local.get 1
    i8x16.add))

  (func (export "splat_i32x4") (param i32) (result v128)
    local.get 0
    i32x4.splat))

Rust Type Mapping

Rust Type	WASM Type
i32	i32
i64	i64
f32	f32
f64	f64
&[i32]	Linear memory slice
&str	Pointer + length
&[u8]	Linear memory slice
String	Pointer + length (allocated)

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