From cebb3e220c62b9fbe896b474391c3e26c380082c Mon Sep 17 00:00:00 2001
From: vbuterin <v@buterin.com>
Date: Wed, 26 Apr 2017 05:04:58 -0400
Subject: [PATCH] Update blockhash_refactoring.md

---
 EIPS/blockhash_refactoring.md | 52 +++++++++++++++++++++--------------
 1 file changed, 32 insertions(+), 20 deletions(-)

diff --git a/EIPS/blockhash_refactoring.md b/EIPS/blockhash_refactoring.md
index eb7a25ed..6e902fdf 100644
--- a/EIPS/blockhash_refactoring.md
+++ b/EIPS/blockhash_refactoring.md
@@ -23,7 +23,7 @@ Stores blockhashes in the state, reducing the protocol complexity and the need f
 
 If `block.number == METROPOLIS_FORK_BLKNUM`, then when processing the block, before processing any transactions set the code of BLOCKHASH_CONTRACT_ADDR to BLOCKHASH_CONTRACT_CODE.
 
-If `block.number >= METROPOLIS_FORK_BLKNUM`, then when processing a block, before processing any transactions execute a call with the parameters:
+If `block.number >= METROPOLIS_FORK_BLKNUM + 256`, then when processing a block, before processing any transactions execute a call with the parameters:
 
 * `SENDER`: SUPER_USER
 * `GAS`: 1000000
@@ -39,32 +39,44 @@ If `block.number >= METROPOLIS_FORK_BLKNUM + 256`, then the BLOCKHASH opcode ins
 * `VALUE`: 0
 * `DATA`: 32 byte zero-byte-leftpadded integer representing the stack argument with which the opcode was called
 
-Also, the gas cost is increased from 20 to 350 to reflect the higher costs of processing the algorithm in the contract code.
+Also, the gas cost is increased from 20 to 800 to reflect the higher costs of processing the algorithm in the contract code.
 
 ### BLOCKHASH_CONTRACT_CODE
 
-BLOCKHASH_CONTRACT_CODE is set to the compile output of the following Serpent code:
+BLOCKHASH_CONTRACT_CODE is set to:
+
+```
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
+```
+
+The Serpent source code is:
 
 ```python
-if msg.sender == {SUPERUSER}:
-    prevblock_number = block.number - 1
-    ~sstore(prevblock_number % 256, ~calldataload(0))
-    if prevblock_number % 256 == 0:
-        ~sstore(256 + (prevblock_number / 256) % 256, ~calldataload(0))
-    if prevblock_number % 65536 == 0:
-        ~sstore(512 + (prevblock_number / 65536) % 256, ~calldataload(0))
+# Setting the block hash
+if msg.sender == 2**160 - 2:
+    with prev_block_number = block.number - 1:
+        # Use storage fields 0..255 to store the last 256 hashes
+        ~sstore(prev_block_number % 256, ~calldataload(0))
+        # Use storage fields 256..511 to store the hashes of the last 256
+        # blocks with block.number % 256 == 0
+        if not (prev_block_number % 256):
+            ~sstore(256 + (prev_block_number / 256) % 256, ~calldataload(0))
+        # Use storage fields 512..767 to store the hashes of the last 256
+        # blocks with block.number % 65536 == 0
+        if not (prev_block_number % 65536):
+            ~sstore(512 + (prev_block_number / 65536) % 256, ~calldataload(0))
+# Getting the block hash
 else:
-    if ~calldataload(0) >= block.number or ~calldataload(0) < {METROPOLIS_FORK_BLKNUM}:
-        return 0
-    if block.number - ~calldataload(0) >= 256:
-        return ~sload(~calldataload(0) % 256)
-    elif block.number - ~calldataload(0) >= 65536 and ~calldataload(0) % 256 == 0:
-        return ~sload(256 + (~calldataload(0) / 256) % 256)
-    elif block.number - ~calldataload(0) >= 16777216 and ~calldataload(0) % 65536 == 0:
-        return ~sload(512 + (~calldataload(0) / 65536) % 256)
+    if ~calldataload(0) >= block.number:
+        return(0)
+    elif block.number - ~calldataload(0) <= 256:
+        return(~sload(~calldataload(0) % 256))
+    elif (not (~calldataload(0) % 256) and block.number - ~calldataload(0) <= 65536):
+        return(~sload(256 + (~calldataload(0) / 256) % 256))
+    elif (not (~calldataload(0) % 65536) and block.number - ~calldataload(0) <= 16777216):
+        return(~sload(512 + (~calldataload(0) / 65536) % 256))
     else:
-        return 0
-        
+        return(~calldataload(0) % 256 == 0)
 ```
 
 ### Rationale