Calculating the GCD
You can also browse this source code online and clone the wasmtime repository to run the example locally.
This example shows off how run a wasm program which calculates the GCD of two numbers.
gcd.wat
(module
(func $gcd (param i32 i32) (result i32)
(local i32)
block ;; label = @1
block ;; label = @2
local.get 0
br_if 0 (;@2;)
local.get 1
local.set 2
br 1 (;@1;)
end
loop ;; label = @2
local.get 1
local.get 0
local.tee 2
i32.rem_u
local.set 0
local.get 2
local.set 1
local.get 0
br_if 0 (;@2;)
end
end
local.get 2
)
(export "gcd" (func $gcd))
)
gcd.rs
//! Example of instantiating of the WebAssembly module and invoking its exported
//! function.
// You can execute this example with `cargo run --example gcd`
use anyhow::Result;
use wasmtime::*;
fn main() -> Result<()> {
// Load our WebAssembly (parsed WAT in our case), and then load it into a
// `Module` which is attached to a `Store` cache. After we've got that we
// can instantiate it.
let store = Store::default();
let module = Module::from_file(store.engine(), "examples/gcd.wat")?;
let instance = Instance::new(&store, &module, &[])?;
// Invoke `gcd` export
let gcd = instance
.get_func("gcd")
.ok_or(anyhow::format_err!("failed to find `gcd` function export"))?
.get2::<i32, i32, i32>()?;
println!("gcd(6, 27) = {}", gcd(6, 27)?);
Ok(())
}