diff --git a/TODO.md b/TODO.md
index 16ab05f..70c6169 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,6 +1,6 @@
 ## Bytecode
 
-- [ ] Byte array
+- [x] Byte array
   - Auto-expand
   - Add/retrive byte/int/float/string
   - Should not be larger than the byte array itself
diff --git a/src/bytecode/bytearray.cc b/src/bytecode/bytearray.cc
index c29cc85..9968642 100644
--- a/src/bytecode/bytearray.cc
+++ b/src/bytecode/bytearray.cc
@@ -1 +1,84 @@
 #include "bytearray.hh"
+
+#include <cstring>
+
+namespace tyche {
+
+void ByteArray::add_byte(uint32_t addr, uint8_t byte)
+{
+    try {
+        data_.at(addr) = byte;
+    } catch (std::out_of_range&) {
+        data_.resize(addr + 1, 0);
+        data_.at(addr) = byte;
+    }
+}
+
+void ByteArray::add_int(uint32_t addr, int32_t value)
+{
+    uint32_t zz = ((uint32_t)(value << 1)) ^ ((uint32_t)(value >> 31));
+    while (zz > 0x7F) {
+        add_byte(addr++, (zz & 0x7F) | 0x80);
+        zz >>= 7;
+    }
+    add_byte(addr, zz & 0x7F);
+}
+
+void ByteArray::add_float(uint32_t addr, float value)
+{
+    uint32_t bits;
+    std::memcpy(&bits, &value, 4);
+    add_byte(addr, (uint8_t)(bits));
+    add_byte(addr+1, (uint8_t)(bits >> 8));
+    add_byte(addr+2, (uint8_t)(bits >> 16));
+    add_byte(addr+3, (uint8_t)(bits >> 24));
+}
+
+void ByteArray::add_string(uint32_t addr, std::string const& str)
+{
+    for (uint8_t c: str)
+        add_byte(addr++, c);
+    add_byte(addr, 0);
+}
+
+uint8_t ByteArray::get_byte(uint32_t addr) const
+{
+    return data_.at(addr);
+}
+
+std::pair<int32_t, size_t> ByteArray::get_int(uint32_t addr) const
+{
+    uint32_t zz = 0;
+    int shift = 0;
+    for (size_t i = 0; shift < 35; i++) {
+        uint8_t byte = get_byte(addr++);
+        zz |= (uint32_t)(byte & 0x7F) << shift;
+        if (!(byte & 0x80)) {
+            int32_t value = (int32_t)((zz >> 1) ^ -(zz & 1));
+            return std::make_pair(value, (int)(i + 1));
+        }
+        shift += 7;
+    }
+    throw BytecodeParsingError("Error parsing int32 at position " + std::to_string(addr));
+}
+
+std::pair<float, size_t> ByteArray::get_float(uint32_t addr) const
+{
+    uint32_t bits = (uint32_t) get_byte(addr)
+            | (uint32_t) get_byte(addr+1) << 8
+            | (uint32_t) get_byte(addr+2) << 16
+            | (uint32_t) get_byte(addr+3) << 24;
+    float value;
+    std::memcpy(&value, &bits, 4);
+    return { value, 4 };
+}
+
+std::pair<std::string, size_t> ByteArray::get_string(uint32_t addr) const
+{
+    std::string data;
+    while (char c = (char) get_byte(addr++))
+        data += c;
+    return { data, data.size() + 1 };
+}
+
+}
\ No newline at end of file
diff --git a/src/bytecode/bytearray.hh b/src/bytecode/bytearray.hh
index a9e0778..a7d5b85 100644
--- a/src/bytecode/bytearray.hh
+++ b/src/bytecode/bytearray.hh
@@ -1,8 +1,36 @@
 #ifndef TYCHE_BYTEARRAY_HH
 #define TYCHE_BYTEARRAY_HH
 
-class ByteArray {
+#include <cstdint>
+#include <stdexcept>
+#include <string>
+#include <vector>
 
+namespace tyche {
+
+class ByteArray {
+public:
+    void add_byte(uint32_t addr, uint8_t byte);
+    void add_int(uint32_t addr, int32_t value);
+    void add_float(uint32_t addr, float value);
+    void add_string(uint32_t addr, std::string const& str);
+
+    [[nodiscard]] uint8_t                        get_byte(uint32_t addr) const;
+    [[nodiscard]] std::pair<int32_t, size_t>     get_int(uint32_t addr) const;
+    [[nodiscard]] std::pair<float, size_t>       get_float(uint32_t addr) const;
+    [[nodiscard]] std::pair<std::string, size_t> get_string(uint32_t addr) const;
+
+    [[nodiscard]] std::vector<uint8_t> const& data() const { return data_; }
+
+private:
+    std::vector<uint8_t> data_;
 };
 
+class BytecodeParsingError : public std::runtime_error {
+public:
+    explicit BytecodeParsingError(std::string const& str) : std::runtime_error(str.c_str()) {}
+};
+
+}
+
 #endif //TYCHE_BYTEARRAY_HH
diff --git a/src/bytecode/tests.cc b/src/bytecode/tests.cc
index 8bb1668..7d5ab87 100644
--- a/src/bytecode/tests.cc
+++ b/src/bytecode/tests.cc
@@ -1,8 +1,41 @@
 #include "gtest/gtest.h"
 
-TEST(test, test)
+#include <cstring>
+#include <functional>
+
+#include "bytearray.hh"
+
+using namespace tyche;
+
+TEST(ByteArray, ByteArray)
 {
-    ASSERT_EQ(1, 1);
+    auto test = [](std::function<void(ByteArray&)> const& f, std::vector<uint8_t> const& expected) {
+        ByteArray ba;
+        f(ba);
+        ASSERT_EQ(ba.data().size(), expected.size());
+        ASSERT_EQ(std::memcmp(ba.data().data(), expected.data(), ba.data().size()), 0);
+    };
+
+#define TESTX(a, ...) test([](ByteArray& ba) { a; }, std::vector<uint8_t>({ __VA_ARGS__ }));
+
+    TESTX(ba.add_byte(1, 0xab), 0x00, 0xab)
+
+    ByteArray ba;
+    ba.add_byte(1, 0xab); ASSERT_EQ(ba.get_byte(1), 0xab);
+
+    ba.add_int(1, 12); ASSERT_EQ(ba.get_int(1), std::make_pair(12, 1));
+    ba.add_int(1, -12); ASSERT_EQ(ba.get_int(1), std::make_pair(-12, 1));
+    ba.add_int(1, 5000); ASSERT_EQ(ba.get_int(1), std::make_pair(5000, 2));
+    ba.add_int(1, 5000300); ASSERT_EQ(ba.get_int(1), std::make_pair(5000300, 4));
+    ba.add_int(1, -5000300); ASSERT_EQ(ba.get_int(1), std::make_pair(-5000300, 4));
+
+    ba.add_float(1, 3.14); ASSERT_FLOAT_EQ(ba.get_float(1).first, 3.14);
+    ba.add_float(1, -3.14); ASSERT_FLOAT_EQ(ba.get_float(1).first, -3.14);
+    ba.add_float(1, -5000300.1324); ASSERT_FLOAT_EQ(ba.get_float(1).first, -5000300.1324);
+
+    ba.add_string(1, "Hello world!"); ASSERT_EQ(ba.get_string(1), std::make_pair("Hello world!", 13));
+
+#undef TESTX
 }
 
 int main(int argc, char** argv)