# Fuel ASM
[](https://github.com/FuelLabs/fuel-asm/actions/workflows/ci.yml)
[](https://crates.io/crates/fuel-asm)
[](https://docs.rs/fuel-asm/)
[](https://discord.gg/xfpK4Pe)
Instruction set for the [FuelVM](https://github.com/FuelLabs/fuel-specs).
## Compile features
- `std`: Unless set, the crate will link to the core-crate instead of the std-crate. More info [here](https://docs.rust-embedded.org/book/intro/no-std.html).
- `serde`: Add support for [serde](https://crates.io/crates/serde) for the types exposed by this crate.
## Example
```rust
use fuel_asm::*;
use Opcode::*;
// A sample program to perform ecrecover
let program = vec![
MOVE(0x10, 0x01), // set r[0x10] := $one
SLLI(0x20, 0x10, 5), // set r[0x20] := `r[0x10] << 5 == 32`
SLLI(0x21, 0x10, 6), // set r[0x21] := `r[0x10] << 6 == 64`
ALOC(0x21), // alloc `r[0x21] == 64` to the heap
ADDI(0x10, 0x07, 1), // set r[0x10] := `$hp + 1` (allocated heap)
MOVE(0x11, 0x04), // set r[0x11] := $ssp
ADD(0x12, 0x04, 0x20), // set r[0x12] := `$ssp + r[0x20]`
ECR(0x10, 0x11, 0x12), // recover public key in memory[r[0x10], 64]
RET(0x01), // return `1`
];
// Convert program to bytes representation
let bytes: Vec<u8> = program.iter().copied().collect();
// A program can be reconstructed from an iterator of bytes
let restored = Opcode::from_bytes_iter(bytes.iter().copied());
assert_eq!(program, restored);
// Every instruction can be described as `u32` big-endian bytes
let halfwords: Vec<u32> = program.iter().copied().map(u32::from).collect();
let bytes = halfwords.iter().copied().map(u32::to_be_bytes).flatten();
let restored = Opcode::from_bytes_iter(bytes);
assert_eq!(program, restored);
// We can also reconstruct the instructions individually
let restored: Vec<Opcode> = halfwords.iter().copied().map(Opcode::from).collect();
assert_eq!(program, restored);
// We have an unchecked variant for optimal performance
let restored: Vec<Opcode> = halfwords
.iter()
.copied()
.map(|w| unsafe { Opcode::from_bytes_unchecked(&w.to_be_bytes()) })
.collect();
assert_eq!(program, restored);
// Finally, we have [`Instruction`] to allow optimal runtime parsing of the components of the
// opcode
//
// `Opcode` itself is only but an abstraction/helper to facilitate visualization, but the VM is
// expected to use raw instructions
let instrs: Vec<Instruction> = program.iter().copied().map(Instruction::from).collect();
let restored: Vec<Opcode> = instrs.iter().copied().map(Opcode::from).collect();
assert_eq!(program, restored);
// An instruction is composed by the opcode representation registers Id and immediate values
assert_eq!(instrs[1].op(), OpcodeRepr::SLLI as u8);
assert_eq!(instrs[1].ra(), 0x20);
assert_eq!(instrs[1].rb(), 0x10);
assert_eq!(instrs[1].imm12(), 5);
```