ec-recover (FuelLabs#5)

* Add ecr lib

* Add todo comment

* Add recover_pubkey and refactor ecr

* Fixup

* Update comments

* Add comments to ec-recover asm block

* Modify asm

* Clean up asm

* Fix B512 field assignment

* Fix ordering of lib deps

* Remove ec_recover, to be added in separate PR

* Clean up comments

src/ecr.sw

@@ -0,0 +1,19 @@
+library ecr;
+
+use ::b512::B512;
+use ::address::Address;
+
+/// Recover the address derived from the private key used to sign a message
+pub fn ec_recover_address(signature: B512, msg_hash: b256) -> Address {
+    let address = asm(pub_key_buffer, sig_ptr: signature.hi, hash: msg_hash, addr_buffer, sixty_four: 64) {
+        move pub_key_buffer sp; // mv sp to pub_key result buffer.
+        cfei i64;
+        ecr pub_key_buffer sig_ptr hash; // recover public_key from sig & hash
+        move addr_buffer sp; // mv sp to addr result buffer.
+        cfei i32;
+        s256 addr_buffer pub_key_buffer sixty_four; // hash 64 bytes to the addr_buffer
+        addr_buffer: b256
+    };
+
+    ~Address::from(address)
+}

src/lib.sw

@@ -10,5 +10,6 @@ dep context;
 dep address;
 dep block;
 dep result;
+dep ecr;
 
 use core::*;