specs: cleanup guaranteed-gas-market (#8740)

Deduplicates some constants and ensures a single source of truth
for defining values. Helps to reduce confusion when reading the specs.
These specs are important for understanding the security properties
of the ecotone upgrade where system upgrade transactions are used
to trigger a hardfork upgrade of L2 predeploys. The invariant must
be held that it is not possible to create an L2 block that is larger
than the block gas limit when it contains all of the user deposits
plus the upgrade txs.

specs/guaranteed-gas-market.md

@@ -40,14 +40,15 @@ of this credit is greater than the ETH value of the requested guaranteed gas
 
 ## Default Values
 
-| Variable                        | Value             |
-| ------------------------------- | ----------------- |
-| Max Resource Limit              | 20,000,000        |
-| Elasticity Multiplier           | 10                |
-| Base Fee Max Change Denominator | 8                 |
-| Minimum Base Fee                | 1 gwei            |
-| Maximum Base Fee                | type(uint128).max |
-| System Tx Max Gas               | 1,000,000         |
+| Variable                         | Value                                          |
+| -------------------------------- | ---------------------------------------------- |
+| `MAX_RESOURCE_LIMIT`             | 20,000,000                                     |
+| `ELASTICITY_MULTIPLIER`          | 10                                             |
+| `BASEFEE_MAX_CHANGE_DENOMINATOR` | 8                                              |
+| `MINIMUM_BASEFEE`                | 1 gwei                                         |
+| `MAXIMUM_BASEFEE`                | type(uint128).max                              |
+| `SYSTEM_TX_MAX_GAS`              | 1,000,000                                      |
+| `TARGET_RESOURCE_LIMIT`          | `MAX_RESOURCE_LIMIT` / `ELASTICITY_MULTIPLIER` |
 
 ## Limiting Guaranteed Gas
 
@@ -55,9 +56,9 @@ The total amount of guaranteed gas that can be bought in a single L1 block must
 prevent a denial of service attack against L2 as well as ensure the total amount of guaranteed gas
 stays below the L2 block gas limit.
 
-We set a guaranteed gas limit of 8,000,000 gas per L1 block and a target of 2,000,000 gas per L1
-block. These numbers enabled occasional large transactions while staying within our target and
-maximum gas usage on L2.
+We set a guaranteed gas limit of `MAX_RESOURCE_LIMIT` gas per L1 block and a target of
+`MAX_RESOURCE_LIMIT` / `ELASTICITY_MULTIPLIER` gas per L1 block. These numbers enabled
+occasional large transactions while staying within our target and maximum gas usage on L2.
 
 Because the amount of guaranteed L2 gas that can be purchased in a single block is now limited,
 we implement an EIP-1559-style fee market to reduce congestion on deposits. By setting the limit
@@ -67,11 +68,6 @@ at a multiple of the target, we enable deposits to temporarily use more L2 gas a
 # Pseudocode to update the L2 Deposit Basefee and cap the amount of guaranteed gas
 # bought in a block. Calling code must handle the gas burn and validity checks on
 # the ability of the account to afford this gas.
-BASE_FEE_MAX_CHANGE_DENOMINATOR = 8
-ELASTICITY_MULTIPLIER = 4
-MAX_RESOURCE_LIMIT = 8_000_000
-TARGET_RESOURCE_LIMIT = MAX_RESOURCE_LIMIT / ELASTICITY_MULTIPLIER
-MINIMUM_BASEFEE = 10000
 
 # prev_basefee is a u128, prev_bought_gas and prev_num are u64s
 prev_basefee, prev_bought_gas, prev_num = <values from previous update>
@@ -98,7 +94,7 @@ elif prev_num != now_num:
     gas_used_delta = int128(prev_bought_gas) - int128(TARGET_RESOURCE_LIMIT)
     # Use truncating (round to 0) division - solidity's default.
     # Sign extend gas_used_delta & prev_basefee to 256 bits to avoid overflows here.
-    base_fee_per_gas_delta = prev_basefee * gas_used_delta / TARGET_RESOURCE_LIMIT / BASE_FEE_MAX_CHANGE_DENOMINATOR
+    base_fee_per_gas_delta = prev_basefee * gas_used_delta / TARGET_RESOURCE_LIMIT / BASEFEE_MAX_CHANGE_DENOMINATOR
     now_basefee_wide = prev_basefee + base_fee_per_gas_delta
 
     now_basefee = clamp(now_basefee_wide, min=MINIMUM_BASEFEE, max=UINT_128_MAX_VALUE)
@@ -111,7 +107,7 @@ elif prev_num != now_num:
     if prev_num + 1 < now_num:
         n = now_num - prev_num - 1
         # Apply 7/8 reduction to prev_basefee for the n empty blocks in a row.
-        now_basefee_wide = now_basefee * pow(1-(1/BASE_FEE_MAX_CHANGE_DENOMINATOR), n)
+        now_basefee_wide = now_basefee * pow(1-(1/BASEFEE_MAX_CHANGE_DENOMINATOR), n)
         now_basefee = clamp(now_basefee_wide, min=MINIMUM_BASEFEE, max=type(uint128).max)
 
 require(now_bought_gas < MAX_RESOURCE_LIMIT)