Feat/Hashers: Implement sha256d :fixes #3

src/hashes/sha256d.zig

@@ -0,0 +1,56 @@
+const std = @import("std");
+const Hash = std.crypto.sha256;
+
+pub const HashEngine = struct {
+    sha256_engine: Hash.Context,
+
+    pub fn new() HashEngine {
+        return HashEngine{
+            .sha256_engine = Hash.Context.init(),
+        };
+    }
+
+    pub fn input(self: *HashEngine, data: []const u8) void {
+        self.sha256_engine.update(data);
+    }
+
+    pub fn n_bytes_hashed(self: *const HashEngine) usize {
+        return self.sha256_engine.total_len;
+    }
+
+    pub fn final(self: *HashEngine) []u8 {
+        var sha1_result: [32]u8 = undefined;
+        self.sha256_engine.final(&sha1_result);
+
+        var sha2_result: [32]u8 = undefined;
+        var second_sha256 = Hash.hash(sha1_result[0..]);
+        std.mem.copy(u8, sha2_result[0..], second_sha256[0..]);
+
+        return sha2_result[0..];
+    }
+};
+
+// Test cases
+test "double SHA256 (SHA256d)" {
+    const input = "hello world";
+    var engine = HashEngine.new();
+    engine.input(input);
+
+    const expected_hash: [32]u8 = [_]u8{ 0xb9, 0x4d, 0x27, 0xb9, 0x93, 0x4d, 0x3e, 0x08, 0xa5, 0x2e, 0x52, 0xd7, 0xda, 0x7d, 0xab, 0xfa, 0xc4, 0x6e, 0x0f, 0xf4, 0x78, 0x91, 0x87, 0x3c, 0xc8, 0x89, 0x3f, 0xbe, 0x58, 0x68, 0xb2, 0x38 };
+
+    const result = engine.final();
+
+    try std.testing.expect(std.mem.eql(u8, result, expected_hash));
+}
+
+test "empty string double SHA256 (SHA256d)" {
+    const input = "";
+    var engine = HashEngine.new();
+    engine.input(input);
+
+    const expected_hash: [32]u8 = [_]u8{ 0x5d, 0xf6, 0xe0, 0xe2, 0x76, 0x13, 0x59, 0xd3, 0x0a, 0x82, 0x75, 0x05, 0x8e, 0x29, 0x9f, 0xcc, 0x03, 0x81, 0x53, 0x45, 0x45, 0xf5, 0x5c, 0xf4, 0x3e, 0x41, 0x98, 0x3f, 0x5d, 0x4c, 0x94, 0x56 };
+
+    const result = engine.final();
+
+    try std.testing.expect(std.mem.eql(u8, result, expected_hash));
+}