From c60afbe4499babe884b19adbb06f806e8b6e4914 Mon Sep 17 00:00:00 2001
From: julienbrs <julien.bourseau@gmail.com>
Date: Sat, 18 Nov 2023 19:16:52 +0100
Subject: [PATCH 1/5] docs + contracts + test

---
 .../hash_solidity_compatible/.gitignore       |  1 +
 .../hash_solidity_compatible/Scarb.lock       |  6 +++
 .../hash_solidity_compatible/Scarb.toml       |  8 ++++
 .../src/hash_solidity_compatible.cairo        | 41 +++++++++++++++++++
 .../hash_solidity_compatible/src/lib.cairo    |  4 ++
 .../hash_solidity_compatible/src/tests.cairo  | 33 +++++++++++++++
 src/SUMMARY.md                                |  1 +
 src/ch02/hash-solidity-compatible.md          | 11 +++++
 src/ch02/hash_solidity_compatible.md          |  1 +
 9 files changed, 106 insertions(+)
 create mode 100644 listings/ch02-advanced-concepts/hash_solidity_compatible/.gitignore
 create mode 100644 listings/ch02-advanced-concepts/hash_solidity_compatible/Scarb.lock
 create mode 100644 listings/ch02-advanced-concepts/hash_solidity_compatible/Scarb.toml
 create mode 100644 listings/ch02-advanced-concepts/hash_solidity_compatible/src/hash_solidity_compatible.cairo
 create mode 100644 listings/ch02-advanced-concepts/hash_solidity_compatible/src/lib.cairo
 create mode 100644 listings/ch02-advanced-concepts/hash_solidity_compatible/src/tests.cairo
 create mode 100644 src/ch02/hash-solidity-compatible.md
 create mode 100644 src/ch02/hash_solidity_compatible.md

diff --git a/listings/ch02-advanced-concepts/hash_solidity_compatible/.gitignore b/listings/ch02-advanced-concepts/hash_solidity_compatible/.gitignore
new file mode 100644
index 00000000..1de56593
--- /dev/null
+++ b/listings/ch02-advanced-concepts/hash_solidity_compatible/.gitignore
@@ -0,0 +1 @@
+target
\ No newline at end of file
diff --git a/listings/ch02-advanced-concepts/hash_solidity_compatible/Scarb.lock b/listings/ch02-advanced-concepts/hash_solidity_compatible/Scarb.lock
new file mode 100644
index 00000000..195fb297
--- /dev/null
+++ b/listings/ch02-advanced-concepts/hash_solidity_compatible/Scarb.lock
@@ -0,0 +1,6 @@
+# Code generated by scarb DO NOT EDIT.
+version = 1
+
+[[package]]
+name = "hash_solidity_compatible"
+version = "0.1.0"
diff --git a/listings/ch02-advanced-concepts/hash_solidity_compatible/Scarb.toml b/listings/ch02-advanced-concepts/hash_solidity_compatible/Scarb.toml
new file mode 100644
index 00000000..35d7a5fc
--- /dev/null
+++ b/listings/ch02-advanced-concepts/hash_solidity_compatible/Scarb.toml
@@ -0,0 +1,8 @@
+[package]
+name = "hash_solidity_compatible"
+version = "0.1.0"
+
+[dependencies]
+starknet = ">=2.3.0"
+
+[[target.starknet-contract]]
\ No newline at end of file
diff --git a/listings/ch02-advanced-concepts/hash_solidity_compatible/src/hash_solidity_compatible.cairo b/listings/ch02-advanced-concepts/hash_solidity_compatible/src/hash_solidity_compatible.cairo
new file mode 100644
index 00000000..cd1a5623
--- /dev/null
+++ b/listings/ch02-advanced-concepts/hash_solidity_compatible/src/hash_solidity_compatible.cairo
@@ -0,0 +1,41 @@
+#[starknet::interface]
+trait ISolidityHashExample<TContractState> {
+    fn hash_data(ref self: TContractState, input_data: Span<u256>);
+    fn get_hashed_value(self: @TContractState) -> u256;
+}
+
+
+#[starknet::contract]
+mod SolidityHashExample {
+    use keccak::{keccak_u256s_be_inputs};
+    use array::Span;
+
+    #[storage]
+    struct Storage {
+        solidity_hash_value: u256,
+    }
+
+    #[abi(embed_v0)]
+    impl SolidityHashExample of super::ISolidityHashExample<ContractState> {
+        fn hash_data(ref self: ContractState, input_data: Span<u256>) {
+            let hashed = keccak_u256s_be_inputs(input_data);
+
+            // Split the hashed value into two 128-bit segments
+            let low: u128 = hashed.low;
+            let high: u128 = hashed.high;
+
+            // Reverse each 128-bit segment
+            let reversed_low = integer::u128_byte_reverse(low);
+            let reversed_high = integer::u128_byte_reverse(high);
+
+            // Reverse merge the reversed segments back into a u256 value
+            let compatible_hash = u256 { low: reversed_high, high: reversed_low };
+
+            self.solidity_hash_value.write(compatible_hash);
+        }
+
+        fn get_hashed_value(self: @ContractState) -> u256 {
+            self.solidity_hash_value.read()
+        }
+    }
+}
diff --git a/listings/ch02-advanced-concepts/hash_solidity_compatible/src/lib.cairo b/listings/ch02-advanced-concepts/hash_solidity_compatible/src/lib.cairo
new file mode 100644
index 00000000..1225e6c3
--- /dev/null
+++ b/listings/ch02-advanced-concepts/hash_solidity_compatible/src/lib.cairo
@@ -0,0 +1,4 @@
+mod hash_solidity_compatible;
+
+#[cfg(test)]
+mod tests;
diff --git a/listings/ch02-advanced-concepts/hash_solidity_compatible/src/tests.cairo b/listings/ch02-advanced-concepts/hash_solidity_compatible/src/tests.cairo
new file mode 100644
index 00000000..9f636da0
--- /dev/null
+++ b/listings/ch02-advanced-concepts/hash_solidity_compatible/src/tests.cairo
@@ -0,0 +1,33 @@
+mod tests {
+    use hash_solidity_compatible::{
+        hash_solidity_compatible::{SolidityHashExample, ISolidityHashExample}
+    };
+    use debug::PrintTrait;
+
+    use starknet::{
+        ContractAddress, get_contract_address, contract_address_const, call_contract_syscall,
+        testing::{set_contract_address}
+    };
+
+    fn setup() -> SolidityHashExample::ContractState {
+        let mut state = SolidityHashExample::contract_state_for_testing();
+        let contract_address = contract_address_const::<0x1>();
+        set_contract_address(contract_address);
+        state
+    }
+
+    #[test]
+    #[available_gas(2000000000)]
+    fn get_same_hash_solidity() {
+        let mut state = setup();
+        let mut array: Array<u256> = ArrayTrait::new();
+        array.append(1);
+
+        let hashExpected: u256 = 0xb10e2d527612073b26eecdfd717e6a320cf44b4afac2b0732d9fcbe2b7fa0cf6;
+
+        let hash = state.hash_data(array.span());
+        let hashReceived: u256 = state.get_hashed_value();
+
+        assert(hashReceived == hashExpected, 'hashReceived != hashExpected');
+    }
+}
diff --git a/src/SUMMARY.md b/src/SUMMARY.md
index 85a76907..e47987d4 100644
--- a/src/SUMMARY.md
+++ b/src/SUMMARY.md
@@ -42,5 +42,6 @@ Summary
   - [Writing to any storage slot](./ch02/write_to_any_slot.md)
   - [Storing Arrays](./ch02/storing_arrays.md)
   - [Struct as mapping key](./ch02/struct-mapping-key.md)
+  - [Hash Solidity Compatible](./ch02/hash-solidity-compatible.md)
   - [Optimisations](./ch02/optimisations/optimisations.md)
     - [Storage Optimisations](./ch02/optimisations/store_using_packing.md)
diff --git a/src/ch02/hash-solidity-compatible.md b/src/ch02/hash-solidity-compatible.md
new file mode 100644
index 00000000..91a7e1f7
--- /dev/null
+++ b/src/ch02/hash-solidity-compatible.md
@@ -0,0 +1,11 @@
+# Hash Solidity Compatible
+
+This contract demonstrates Keccak hashing in Cairo to match Solidity's keccak256. While both use Keccak, their endianness differs: Cairo is little-endian, Solidity big-endian. The contract achieves compatibility by hashing in big-endian using `keccak_u256s_be_inputs`, and reversing the bytes of the result with `u128_byte_reverse`.
+
+For example:
+
+```rust
+{{#include ../../listings/ch02-advanced-concepts/hash_solidity_compatible/src/hash_solidity_compatible.cairo}}
+```
+
+Visit contract on [Voyager](#) or play with it in [Remix](#).
diff --git a/src/ch02/hash_solidity_compatible.md b/src/ch02/hash_solidity_compatible.md
new file mode 100644
index 00000000..7deeb06f
--- /dev/null
+++ b/src/ch02/hash_solidity_compatible.md
@@ -0,0 +1 @@
+# Hash Solidity Compatible

From 44ebf3a1f506000e9264e5a54c2650b954f673c0 Mon Sep 17 00:00:00 2001
From: julienbrs <julien.bourseau@gmail.com>
Date: Sat, 18 Nov 2023 19:33:02 +0100
Subject: [PATCH 2/5] renaming + link

---
 .../src/{hash_solidity_compatible.cairo => contract.cairo}    | 0
 .../hash_solidity_compatible/src/lib.cairo                    | 2 +-
 .../hash_solidity_compatible/src/tests.cairo                  | 2 +-
 src/ch02/hash-solidity-compatible.md                          | 4 ++--
 src/ch02/hash_solidity_compatible.md                          | 1 -
 5 files changed, 4 insertions(+), 5 deletions(-)
 rename listings/ch02-advanced-concepts/hash_solidity_compatible/src/{hash_solidity_compatible.cairo => contract.cairo} (100%)
 delete mode 100644 src/ch02/hash_solidity_compatible.md

diff --git a/listings/ch02-advanced-concepts/hash_solidity_compatible/src/hash_solidity_compatible.cairo b/listings/ch02-advanced-concepts/hash_solidity_compatible/src/contract.cairo
similarity index 100%
rename from listings/ch02-advanced-concepts/hash_solidity_compatible/src/hash_solidity_compatible.cairo
rename to listings/ch02-advanced-concepts/hash_solidity_compatible/src/contract.cairo
diff --git a/listings/ch02-advanced-concepts/hash_solidity_compatible/src/lib.cairo b/listings/ch02-advanced-concepts/hash_solidity_compatible/src/lib.cairo
index 1225e6c3..11ada17a 100644
--- a/listings/ch02-advanced-concepts/hash_solidity_compatible/src/lib.cairo
+++ b/listings/ch02-advanced-concepts/hash_solidity_compatible/src/lib.cairo
@@ -1,4 +1,4 @@
-mod hash_solidity_compatible;
+mod contract;
 
 #[cfg(test)]
 mod tests;
diff --git a/listings/ch02-advanced-concepts/hash_solidity_compatible/src/tests.cairo b/listings/ch02-advanced-concepts/hash_solidity_compatible/src/tests.cairo
index 9f636da0..15132826 100644
--- a/listings/ch02-advanced-concepts/hash_solidity_compatible/src/tests.cairo
+++ b/listings/ch02-advanced-concepts/hash_solidity_compatible/src/tests.cairo
@@ -1,6 +1,6 @@
 mod tests {
     use hash_solidity_compatible::{
-        hash_solidity_compatible::{SolidityHashExample, ISolidityHashExample}
+        contract::{SolidityHashExample, ISolidityHashExample}
     };
     use debug::PrintTrait;
 
diff --git a/src/ch02/hash-solidity-compatible.md b/src/ch02/hash-solidity-compatible.md
index 91a7e1f7..2f766066 100644
--- a/src/ch02/hash-solidity-compatible.md
+++ b/src/ch02/hash-solidity-compatible.md
@@ -5,7 +5,7 @@ This contract demonstrates Keccak hashing in Cairo to match Solidity's keccak256
 For example:
 
 ```rust
-{{#include ../../listings/ch02-advanced-concepts/hash_solidity_compatible/src/hash_solidity_compatible.cairo}}
+{{#include ../../listings/ch02-advanced-concepts/hash_solidity_compatible/src/contract.cairo}}
 ```
 
-Visit contract on [Voyager](#) or play with it in [Remix](#).
+Visit contract on [Voyager](#) or play with it in [Remix](https://remix.ethereum.org/?#activate=Starknet&url=https://github.com/NethermindEth/StarknetByExample/blob/main/listings/ch02-advanced-concepts/hash_solidity_compatible/src/contract.cairo).
diff --git a/src/ch02/hash_solidity_compatible.md b/src/ch02/hash_solidity_compatible.md
deleted file mode 100644
index 7deeb06f..00000000
--- a/src/ch02/hash_solidity_compatible.md
+++ /dev/null
@@ -1 +0,0 @@
-# Hash Solidity Compatible

From 8afc2cf0e5949a04335788843111758f1f3979b2 Mon Sep 17 00:00:00 2001
From: julienbrs <julien.bourseau@gmail.com>
Date: Sat, 18 Nov 2023 19:45:04 +0100
Subject: [PATCH 3/5] fmt

---
 .../hash_solidity_compatible/src/tests.cairo                  | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/listings/ch02-advanced-concepts/hash_solidity_compatible/src/tests.cairo b/listings/ch02-advanced-concepts/hash_solidity_compatible/src/tests.cairo
index 15132826..464ec571 100644
--- a/listings/ch02-advanced-concepts/hash_solidity_compatible/src/tests.cairo
+++ b/listings/ch02-advanced-concepts/hash_solidity_compatible/src/tests.cairo
@@ -1,7 +1,5 @@
 mod tests {
-    use hash_solidity_compatible::{
-        contract::{SolidityHashExample, ISolidityHashExample}
-    };
+    use hash_solidity_compatible::{contract::{SolidityHashExample, ISolidityHashExample}};
     use debug::PrintTrait;
 
     use starknet::{

From a270848faae6706def63f13fed1f8e66b0b91192 Mon Sep 17 00:00:00 2001
From: julienbrs <julien.bourseau@gmail.com>
Date: Tue, 21 Nov 2023 00:52:56 +0100
Subject: [PATCH 4/5] changes requested

---
 .../hash_solidity_compatible/src/contract.cairo   | 15 ++++-----------
 .../hash_solidity_compatible/src/tests.cairo      |  8 +++-----
 src/ch02/hash-solidity-compatible.md              |  2 +-
 3 files changed, 8 insertions(+), 17 deletions(-)

diff --git a/listings/ch02-advanced-concepts/hash_solidity_compatible/src/contract.cairo b/listings/ch02-advanced-concepts/hash_solidity_compatible/src/contract.cairo
index cd1a5623..5f6f8d24 100644
--- a/listings/ch02-advanced-concepts/hash_solidity_compatible/src/contract.cairo
+++ b/listings/ch02-advanced-concepts/hash_solidity_compatible/src/contract.cairo
@@ -1,7 +1,6 @@
 #[starknet::interface]
 trait ISolidityHashExample<TContractState> {
-    fn hash_data(ref self: TContractState, input_data: Span<u256>);
-    fn get_hashed_value(self: @TContractState) -> u256;
+    fn hash_data(ref self: TContractState, input_data: Span<u256>) -> u256;
 }
 
 
@@ -11,13 +10,11 @@ mod SolidityHashExample {
     use array::Span;
 
     #[storage]
-    struct Storage {
-        solidity_hash_value: u256,
-    }
+    struct Storage {}
 
     #[abi(embed_v0)]
     impl SolidityHashExample of super::ISolidityHashExample<ContractState> {
-        fn hash_data(ref self: ContractState, input_data: Span<u256>) {
+        fn hash_data(ref self: ContractState, input_data: Span<u256>) -> u256 {
             let hashed = keccak_u256s_be_inputs(input_data);
 
             // Split the hashed value into two 128-bit segments
@@ -31,11 +28,7 @@ mod SolidityHashExample {
             // Reverse merge the reversed segments back into a u256 value
             let compatible_hash = u256 { low: reversed_high, high: reversed_low };
 
-            self.solidity_hash_value.write(compatible_hash);
-        }
-
-        fn get_hashed_value(self: @ContractState) -> u256 {
-            self.solidity_hash_value.read()
+            compatible_hash
         }
     }
 }
diff --git a/listings/ch02-advanced-concepts/hash_solidity_compatible/src/tests.cairo b/listings/ch02-advanced-concepts/hash_solidity_compatible/src/tests.cairo
index 464ec571..43709a54 100644
--- a/listings/ch02-advanced-concepts/hash_solidity_compatible/src/tests.cairo
+++ b/listings/ch02-advanced-concepts/hash_solidity_compatible/src/tests.cairo
@@ -21,11 +21,9 @@ mod tests {
         let mut array: Array<u256> = ArrayTrait::new();
         array.append(1);
 
-        let hashExpected: u256 = 0xb10e2d527612073b26eecdfd717e6a320cf44b4afac2b0732d9fcbe2b7fa0cf6;
+        let hash_expected: u256 = 0xb10e2d527612073b26eecdfd717e6a320cf44b4afac2b0732d9fcbe2b7fa0cf6;
+        let hash_received: u256 = state.hash_data(array.span());
 
-        let hash = state.hash_data(array.span());
-        let hashReceived: u256 = state.get_hashed_value();
-
-        assert(hashReceived == hashExpected, 'hashReceived != hashExpected');
+        assert(hash_received == hash_expected, 'hash_received != hash_expected');
     }
 }
diff --git a/src/ch02/hash-solidity-compatible.md b/src/ch02/hash-solidity-compatible.md
index 2f766066..68f3a2ec 100644
--- a/src/ch02/hash-solidity-compatible.md
+++ b/src/ch02/hash-solidity-compatible.md
@@ -8,4 +8,4 @@ For example:
 {{#include ../../listings/ch02-advanced-concepts/hash_solidity_compatible/src/contract.cairo}}
 ```
 
-Visit contract on [Voyager](#) or play with it in [Remix](https://remix.ethereum.org/?#activate=Starknet&url=https://github.com/NethermindEth/StarknetByExample/blob/main/listings/ch02-advanced-concepts/hash_solidity_compatible/src/contract.cairo).
+Play with the contract in [Remix](https://remix.ethereum.org/?#activate=Starknet&url=https://github.com/NethermindEth/StarknetByExample/blob/main/listings/ch02-advanced-concepts/hash_solidity_compatible/src/contract.cairo).

From d2fdddb416f155e2dc4b6d609b2de18b9a591316 Mon Sep 17 00:00:00 2001
From: julienbrs <julien.bourseau@gmail.com>
Date: Tue, 21 Nov 2023 00:56:44 +0100
Subject: [PATCH 5/5] nit: fmt

---
 .../hash_solidity_compatible/src/tests.cairo                   | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/listings/ch02-advanced-concepts/hash_solidity_compatible/src/tests.cairo b/listings/ch02-advanced-concepts/hash_solidity_compatible/src/tests.cairo
index 43709a54..d1d1726b 100644
--- a/listings/ch02-advanced-concepts/hash_solidity_compatible/src/tests.cairo
+++ b/listings/ch02-advanced-concepts/hash_solidity_compatible/src/tests.cairo
@@ -21,7 +21,8 @@ mod tests {
         let mut array: Array<u256> = ArrayTrait::new();
         array.append(1);
 
-        let hash_expected: u256 = 0xb10e2d527612073b26eecdfd717e6a320cf44b4afac2b0732d9fcbe2b7fa0cf6;
+        let hash_expected: u256 =
+            0xb10e2d527612073b26eecdfd717e6a320cf44b4afac2b0732d9fcbe2b7fa0cf6;
         let hash_received: u256 = state.hash_data(array.span());
 
         assert(hash_received == hash_expected, 'hash_received != hash_expected');