MCOPY spec

specs/opcode/94MCOPY.md

@@ -0,0 +1,40 @@
+# MCOPY opcode
+
+## Procedure
+
+The `MCOPY` opcode pops `dest_offset`, `offset` and `size` from the stack.
+It then copies `size` bytes in the current environment from memory at an `offset` to the memory at a `dest_offset`. For out-of-bounds scenarios - the memory is extended with respective gas cost applied.
+
+The gas cost of `MCOPY` opcode consists of two parts:
+
+1. A constant gas cost: `3 gas`
+2. A dynamic gas cost: cost of memory expansion and copying (variable depending on the `size` copied to memory)
+
+## Constraints
+
+1. OpcodeId check
+
+- opId == OpcodeId(0x5E)
+
+2. State Transition
+
+- rw_counter += 3 stack_reads
+- stack_pointer += 3
+- pc += 1
+- gas += 3 + dynamic_gas_cost
+- reversible_write_counter += 1
+- memory_size
+  - `prev_memory_size` if `size = 0`
+  - `max(prev_memory_size, (offset + size + 31) / 32)` if `size > 0`
+
+3. Lookups: 4
+
+   1. `dest_offset` is at the 1st position of the stack
+   2. `offset` is at the 2nd position of the stack
+   3. `size` is at the 3rd position of the stack
+   4. CopyTable lookup
+
+## Exceptions
+
+1. stack underflow: `1022 <= stack_pointer <= 1024`
+2. out of gas: remaining gas is not enough