store excess blob count in header instead of adjusted-total

Co-authored-by: vbuterin <v@buterin.com>
Co-authored-by: lightclient <lightclient@protonmail.com>

EIPS/eip-4844.md

@@ -235,7 +235,7 @@ def get_origin(tx: SignedBlobTransaction) -> Address:
 ### Header extension
 
 The current header encoding is extended with a new 256-bit unsigned integer field `blob_txs`. This is the running
-total of blob txs included on chain since this EIP was activated. The resulting RLP encoding of the header is therefore:
+total of excess blob txs included on chain since this EIP was activated. The resulting RLP encoding of the header is therefore:
 
 ```
 rlp([
@@ -262,12 +262,9 @@ rlp([
 The value of `blob_txs` can be calculated using the parent header and number of blob transactions in the block.
 
 ```python
-def calc_blob_gas(parent: Header, blob_txs_in_block: int) -> int:
-    # Don't let the new total fall behind the targeted total to avoid
-    # accumulating a long period of very low fees
-    blocks_since_start = header.Number - FORK_BLKNUM
-    targeted_total = blocks_since_start * TARGET_BLOB_TXS_PER_BLOCK
-    return max(header.blob_txs + blob_txs_in_block, targeted_total)
+def calc_excess_blob_txs(parent: Header, blobs: int) -> int:
+    adjusted = parent.blob_txs + blobs
+    return adjusted - min(TARGET_BLOB_TXS_PER_BLOCK, adjusted)
 ```
 
 ### Beacon chain validation
@@ -346,7 +343,7 @@ def get_intrinsic_gas(tx: SignedBlobTransaction, pre_state: ExecState) -> int:
 def get_blob_gas(header: Header) -> int:
     blocks_since_start = get_current_block(pre_state) - FORK_BLKNUM
     targeted_total = blocks_since_start * TARGET_BLOB_TXS_PER_BLOCK
-    actual_total = header.blob_txs
+    actual_total = targeted_total + header.blob_txs
     if actual_total < targeted_total:
         return 0
     else: