validator/fees: Add gas use calculator for ZK circuits

src/validator/fees.rs

@@ -16,5 +16,77 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+use darkfi_sdk::crypto::constants::MERKLE_DEPTH_ORCHARD;
+
+use crate::zkas::{Opcode, VarType, ZkBinary};
+
 /// Fixed fee for verifying Schnorr signatures using the Pallas elliptic curve
 pub const PALLAS_SCHNORR_SIGNATURE_FEE: u64 = 1000;
+
+/// Calculate the gas use for verifying a given zkas circuit.
+/// This function assumes that the zkbin was properly decoded.
+pub fn circuit_gas_use(zkbin: &ZkBinary) -> u64 {
+    let mut accumulator: u64 = 0;
+
+    // Constants each with a cost of 10
+    accumulator += 10 * zkbin.constants.len() as u64;
+
+    // Literals each with a cost of 10 (for now there's only 1 type of literal)
+    accumulator += 10 * zkbin.literals.len() as u64;
+
+    // Witnesses have cost by type
+    for witness in &zkbin.witnesses {
+        let cost = match witness {
+            VarType::Dummy => unreachable!(),
+            VarType::EcPoint => 20,
+            VarType::EcFixedPoint => unreachable!(),
+            VarType::EcFixedPointShort => unreachable!(),
+            VarType::EcFixedPointBase => unreachable!(),
+            VarType::EcNiPoint => 20,
+            VarType::Base => 10,
+            VarType::BaseArray => unreachable!(),
+            VarType::Scalar => 20,
+            VarType::ScalarArray => unreachable!(),
+            VarType::MerklePath => 10 * MERKLE_DEPTH_ORCHARD as u64,
+            VarType::Uint32 => 10,
+            VarType::Uint64 => 10,
+            VarType::Any => 10,
+        };
+
+        accumulator += cost;
+    }
+
+    // Opcodes depending on how heavy they are
+    for opcode in &zkbin.opcodes {
+        let cost = match opcode.0 {
+            Opcode::Noop => unreachable!(),
+            Opcode::EcAdd => 30,
+            Opcode::EcMul => 30,
+            Opcode::EcMulBase => 30,
+            Opcode::EcMulShort => 30,
+            Opcode::EcMulVarBase => 30,
+            Opcode::EcGetX => 5,
+            Opcode::EcGetY => 5,
+            Opcode::PoseidonHash => 20 + 10 * opcode.1.len() as u64,
+            Opcode::MerkleRoot => 10 * MERKLE_DEPTH_ORCHARD as u64,
+            Opcode::BaseAdd => 15,
+            Opcode::BaseMul => 15,
+            Opcode::BaseSub => 15,
+            Opcode::WitnessBase => 10,
+            Opcode::RangeCheck => 60,
+            Opcode::LessThanStrict => 100,
+            Opcode::LessThanLoose => 100,
+            Opcode::BoolCheck => 20,
+            Opcode::CondSelect => 10,
+            Opcode::ZeroCondSelect => 10,
+            Opcode::ConstrainEqualBase => 10,
+            Opcode::ConstrainEqualPoint => 20,
+            Opcode::ConstrainInstance => 10,
+            Opcode::DebugPrint => 100,
+        };
+
+        accumulator += cost;
+    }
+
+    accumulator
+}