Feat/Hashers: Implement sha256d :fixes #3

src/hashes/lib.zig

@@ -1,2 +1,3 @@
 pub const Ripemd160 = @import("ripemd160.zig").Ripemd160;
 pub const Hash160 = @import("hash160.zig").Hash160;
+pub const Sha256d = @import("sha256d.zig").Sha256d;

src/hashes/sha256d.zig

@@ -0,0 +1,59 @@
+const std = @import("std");
+const Hash = std.crypto.hash.sha2.Sha256;
+const testing = std.testing;
+
+pub const Sha256d = struct {
+    const Self = @This();
+
+    sha256_engine: Hash,
+
+    pub fn init() Self {
+        return Sha256d{
+            .sha256_engine = Hash.init(),
+        };
+    }
+
+    pub fn input(self: *Self, data: []const u8) void {
+        self.sha256_engine.update(data);
+    }
+
+    pub fn n_bytes_hashed(self: *const Self) usize {
+        return self.sha256_engine.total_len;
+    }
+
+    pub fn final(self: *Self) [32]u8 {
+        var sha1_result: [32]u8 = undefined;
+        self.sha256_engine.final(&sha1_result);
+
+        var sha2_engine = Hash.init();
+        sha2_engine.update(&sha1_result);
+        sha2_engine.final(&sha1_result);
+
+        return sha1_result;
+    }
+};
+
+// Test cases
+test "double SHA256 (SHA256d)" {
+    const input = "hello world"[0..11];
+    var engine = Sha256d.init();
+    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[0..], &expected_hash));
+}
+
+test "empty string double SHA256 (SHA256d)" {
+    const input = ""[0..];
+    var engine = Sha256d.init();
+    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 testing.expect(std.mem.eql(u8, result[0..], &expected_hash));
+}