power_play/src/base/base_bitbuff.c

// TODO: Safety check that functions taking byte length can't overflow bit conversion (log2(num_bytes) > 61)

////////////////////////////////////////////////////////////
//~ Buff management

BB_Buff BB_AcquireDynamicBuff(u64 arena_reserve)
{
  BB_Buff result = Zi;
  result.arena = AcquireArena(arena_reserve);
  result.is_backed_by_arena = 1;
  return result;
}

void BB_ReleaseDynamicBuff(BB_Buff *bb)
{
  // Only arena bitbuffs need to be released
  if (bb->is_backed_by_arena)
  {
    ReleaseArena(bb->arena);
  }
}

BB_Buff BB_BuffFromString(String s)
{
  BB_Buff result = Zi;
  result.fixed_buffer = s;
  return result;
}

////////////////////////////////////////////////////////////
//~ Writer management

BB_Writer BB_WriterFromBuff(BB_Buff *bb)
{
  BB_Writer result = Zi;
  result.bb = bb;
  if (bb->is_backed_by_arena)
  {
    result.base = ArenaFirst(bb->arena, u8);
  }
  else
  {
    result.base = bb->fixed_buffer.text;
  }
  result.cur_bit = 0;
#if BITBUFF_DEBUG
  result.debug_enabled = 1;
#endif
  return result;
}

// Use this when writing external formats that will not verify bitbuff debug symbols / magic numbers
BB_Writer BB_WriterFromBuffNoDebug(BB_Buff *bb)
{
  BB_Writer result = BB_WriterFromBuff(bb);
#if BITBUFF_DEBUG
  result.debug_enabled = 0;
#endif
  return result;
}

void BB_ResetWriter(BB_Writer *bbw)
{
  bbw->overflowed = 0;
  bbw->cur_bit = 0;
  if (bbw->bb->is_backed_by_arena)
  {
    ResetArena(bbw->bb->arena);
  }
}

// FIXME: Handle overflowed bbw
u64 BB_GetNumBitsWritten(BB_Writer *bbw)
{
  return bbw->cur_bit;
}

// FIXME: Handle overflowed bbw
u64 BB_GetNumBytesWritten(BB_Writer *bbw)
{
  return (bbw->cur_bit + 7) >> 3;
}

// FIXME: Handle overflowed bbw
String BB_GetWritten(Arena *arena, BB_Writer *bbw)
{
  String result = Zi;
  result.len = (bbw->cur_bit + 7) >> 3;
  result.text = PushStructsNoZero(arena, u8, result.len);
  CopyBytes(result.text, bbw->base, result.len);
  return result;
}

// FIXME: Handle overflowed bbw
u8 *BB_GetWrittenRaw(BB_Writer *bbw)
{
  return bbw->base;
}

// Returns 1 if num_bits would cause the writer to overflow its fixed buffer size (if writer is not backed by a dynamic arena bitbuff)
b32 BB_CheckWriterOverflowBits(BB_Writer *bbw, u64 num_bits)
{
  b32 result = 0;
  BB_Buff *bb = bbw->bb;
  if (bbw->overflowed)
  {
    result = 1;
  }
  else
  {
    u64 bytes_needed = (bbw->cur_bit + num_bits + 7) >> 3;
    if (bb->is_backed_by_arena)
    {
      Arena *arena = bb->arena;
      if (bytes_needed >= arena->pos)
      {
        // Grow arena
        u64 push_size = (((bytes_needed - arena->pos) / BB_WriterOverflowArenaPushSize) + 1) * BB_WriterOverflowArenaPushSize;
        PushStructsNoZero(arena, u8, push_size);
      }
    }
    else
    {
      u64 max_len = bb->fixed_buffer.len;
      if (bytes_needed > max_len)
      {
        // Writer overflowed fixed buffer
#if BITBUFF_DEBUG
        Assert(0);
#endif
        result = 1;
        bbw->cur_bit = max_len << 3;
        bbw->overflowed = 1;
      }
    }
  }
  return result;
}

////////////////////////////////////////////////////////////
//~ Align writer

// Align the pos to the next byte
void BB_WriteAlignToNextByte(BB_Writer *bbw)
{
#if BITBUFF_DEBUG
  if ((bbw->cur_bit & 7) != 0)
  {
    BB_WriteDebugMagic(bbw, BB_DebugMagicKind_AlignNextByte, 0);
  }
#endif
  bbw->cur_bit += (8 - (bbw->cur_bit & 7)) & 7;
}

void BB_WriteAlignBytes(BB_Writer *bbw, u64 align)
{
  BB_WriteAlignToNextByte(bbw);
  BB_WriteDebugMagic(bbw, BB_DebugMagicKind_AlignBytes, align);
  if (align > 0)
  {
    u64 new_pos = (bbw->cur_bit >> 3);
    new_pos += (align - 1);
    new_pos -= new_pos % align;
    if (BB_CheckWriterOverflowBits(bbw, (new_pos << 3) - bbw->cur_bit))
    {
      return;
    }
    bbw->cur_bit = new_pos << 3;
  }
}

////////////////////////////////////////////////////////////
//~ Write bits

void BB_WriteUBitsNoMagic(BB_Writer *bbw, u64 value, u8 num_bits)
{
  Assert(num_bits > 0 && (num_bits == 64 || value <= ~(U64Max << num_bits)));  // Bit count must be able to hold value
  if (BB_CheckWriterOverflowBits(bbw, num_bits))
  {
    return;
  }

  u8 offset = bbw->cur_bit & 7;
  if (offset != 0)
  {
    // Write unaligned bits
    u8 *at = bbw->base + (bbw->cur_bit >> 3);
    u8 num_mix_bits = MinU8((8 - offset), num_bits);
    u8 mix_byte = (u8)((value & ((1 << num_mix_bits) - 1)) << offset);
    *at |= mix_byte;
    value >>= num_mix_bits;
    num_bits -= num_mix_bits;
    bbw->cur_bit += num_mix_bits;
  }

  // cur_bit is now aligned to byte
  u8 *at = bbw->base + (bbw->cur_bit >> 3);
  u8 num_bytes = (num_bits + 7) >> 3;
  CopyBytes(at, &value, num_bytes);
  bbw->cur_bit += num_bits;
}

void BB_WriteUBits(BB_Writer *bbw, u64 value, u8 num_bits)
{
  BB_WriteDebugMagic(bbw, BB_DebugMagicKind_UBits, num_bits);
  BB_WriteUBitsNoMagic(bbw, value, num_bits);
}

void BB_WriteIBits(BB_Writer *bbw, i64 value, u8 num_bits)
{
  BB_WriteDebugMagic(bbw, BB_DebugMagicKind_IBits, num_bits);
  u64 ubits;
  if (value >= 0)
  {
    ubits = value;
  }
  else
  {
    ubits = BB_TwosComplimentFromUint(-value, num_bits);
  }
  BB_WriteUBits(bbw, ubits, num_bits);
}

// Returns written bit to make writing delta encoding logic cleaner
b32 BB_WriteBit(BB_Writer *bbw, u8 value)
{
  BB_WriteUBits(bbw, value, 1);
  return value;
}

////////////////////////////////////////////////////////////
//~ Write variable length integers

// Writes a variable length unsigned integer.
// Value is written in chunks of 7 bits w/ 8th bit signaling continuation.
void BB_WriteUV(BB_Writer *bbw, u64 value)
{
  BB_WriteDebugMagic(bbw, BB_DebugMagicKind_UV, 0);
  while (value > 0x7F)
  {
    u8 cont_byte = 0x80 | (value & 0x7F);
    BB_WriteUBits(bbw, cont_byte, 8);
    value >>= 7;
  }
  BB_WriteUBits(bbw, value, 8);
}

// Writes a variable length signed integer.
// Similar to BB_WriteUV, except the 7th bit of the first byte is a sign bit
// indicating that the value is stored in twos compliment.
void BB_WriteIV(BB_Writer *bbw, i64 value)
{
  BB_WriteDebugMagic(bbw, BB_DebugMagicKind_IV, 0);
  u8 sign_bit;
  u64 tc;
  if (value >= 0)
  {
    sign_bit = 0;
    tc = value;
  }
  else
  {
    sign_bit = 1;
    u64 unsigned_value = -value;
    u8 num_bits = 6;
    unsigned_value >>= 6;
    while (unsigned_value > 0)
    {
      num_bits += 7;
      unsigned_value >>= 7;
    }
    num_bits = MinU8(num_bits, 64);
    tc = BB_TwosComplimentFromUint(-value, num_bits);
  }

  // First byte contains not just cont bit, but sign bit as well.
  u8 first_byte = (tc & 0x3F);
  tc >>= 6;
  first_byte |= (tc > 0) << 7;  // Cont bit
  first_byte |= sign_bit << 6;  // Sign bit
  BB_WriteUBits(bbw, first_byte, 8);

  if (tc > 0)
  {
    while (tc > 0x7F)
    {
      u8 cont_byte = 0x80 | (tc & 0x7F);
      BB_WriteUBits(bbw, cont_byte, 8);
      tc >>= 7;
    }
    BB_WriteUBits(bbw, tc, 8);
  }
}

////////////////////////////////////////////////////////////
//~ Write floating point

void BB_WriteF32(BB_Writer *bbw, f32 value)
{
  BB_WriteDebugMagic(bbw, BB_DebugMagicKind_F32, 0);
  BB_WriteUBits(bbw, *(u32 *)&value, 32);
}

void BB_WriteF64(BB_Writer *bbw, f64 value)
{
  BB_WriteDebugMagic(bbw, BB_DebugMagicKind_F64, 0);
  BB_WriteUBits(bbw, *(u64 *)&value, 64);
}

////////////////////////////////////////////////////////////
//~ Write Uid

void BB_WriteUid(BB_Writer *bbw, Uid value)
{
  BB_WriteDebugMagic(bbw, BB_DebugMagicKind_Uid, 128);
  BB_WriteUBits(bbw, value.hi, 64);
  BB_WriteUBits(bbw, value.lo, 64);
}

////////////////////////////////////////////////////////////
//~ Write raw data

void BB_WriteString(BB_Writer *bbw, String s)
{
  BB_WriteDebugMagic(bbw, BB_DebugMagicKind_String, 0);
  BB_WriteUV(bbw, s.len);
  BB_WriteBytes(bbw, s);
}

void BB_WriteBytes(BB_Writer *bbw, String bytes)
{
  // Align start of bytes
  BB_WriteAlignToNextByte(bbw);

  u64 num_bits = bytes.len << 3;
  if (BB_CheckWriterOverflowBits(bbw, num_bits))
  {
    return;
  }

  u8 *at = bbw->base + (bbw->cur_bit >> 3);
  CopyBytes(at, bytes.text, bytes.len);
  bbw->cur_bit += num_bits;
}

void BB_WriteSeekBytes(BB_Writer *bbw, u64 num_bytes)
{
  BB_WriteAlignToNextByte(bbw);

  u64 num_bits = num_bytes << 3;
  if (BB_CheckWriterOverflowBits(bbw, num_bits))
  {
    return;
  }

  bbw->cur_bit += num_bits;
}

////////////////////////////////////////////////////////////
//~ Writer debug

#if BITBUFF_DEBUG
void BB_WriteDebugMarker(BB_Writer *bbw, String name)
{
  bbw->cur_bit += (8 - (bbw->cur_bit & 7)) & 7;
  for (u64 i = 0; i < name.len; ++i)
  {
    BB_WriteUBitsNoMagic(bbw, name.text[i], 8);
  }
}

void BB_WriteDebugMagic(BB_Writer *bbw, BB_DebugMagicKind magic, u8 num_bits)
{
  if (bbw->debug_enabled)
  {
    if (BB_CheckWriterOverflowBits(bbw, 24))
    {
      return;
    }
    u64 magic_ubits = (u64)magic | ((u64)num_bits << 16);
    BB_WriteUBitsNoMagic(bbw, magic_ubits, 24);
  }
}
#endif

////////////////////////////////////////////////////////////
//~ Reader management

BB_Reader BB_ReaderFromBuff(BB_Buff *bb)
{
  BB_Reader result = Zi;
  if (!bb->is_backed_by_arena)
  {
    result.base = bb->fixed_buffer.text;
    result.base_len = bb->fixed_buffer.len;
  }
  else
  {
    Arena *arena = bb->arena;
    result.base = ArenaFirst(arena, u8);
    result.base_len = arena->pos;
  }
  result.cur_bit = 0;
#if BITBUFF_DEBUG
  result.debug_enabled = 1;
#endif
  return result;
}

// Use this when reading from external formats that will not contain bitbuff debug symbols / magic numbers
BB_Reader BB_ReaderFromBuffNoDebug(BB_Buff *bb)
{
  BB_Reader result = BB_ReaderFromBuff(bb);
#if BITBUFF_DEBUG
  result.debug_enabled = 0;
#endif
  return result;
}

// Returns the number of bits read from the bitbuff
// FIXME: Handle overflowed bbr
u64 BB_GetCurrentReaderBit(BB_Reader *bbr)
{
  return bbr->cur_bit;
}

// Returns the number of *full* bytes read from the bitbuff
// FIXME: Handle overflowed bbr
u64 BB_GetCurrentReaderByte(BB_Reader *bbr)
{
  return bbr->cur_bit >> 3;
}

// Returns the number of bits left until the bitbuff overflows
// FIXME: Handle overflowed bbr
u64 BB_NumBitsRemaining(BB_Reader *bbr)
{
  return (bbr->base_len << 3) - bbr->cur_bit;
}

// Returns the number of *full* bytes left until the bitbuff overflows
// FIXME: Handle overflowed bbr
u64 BB_NumBytesRemaining(BB_Reader *bbr)
{
  return bbr->base_len - (bbr->cur_bit >> 3);
}

b32 BB_CheckReaderOverflowBits(BB_Reader *bbr, u64 num_bits)
{
  b32 result = 0;
  if (bbr->overflowed)
  {
    result = 1;
  }
  else
  {
    u64 bits_needed = bbr->cur_bit + num_bits;
    u64 base_len_bits = bbr->base_len << 3;
    if (bits_needed > base_len_bits)
    {
      // Tried to read past bitbuff memory
#if BITBUFF_DEBUG
      Assert(0);
#endif
      result = 1;
      bbr->cur_bit = base_len_bits;
      bbr->overflowed = 1;
    }
  }
  return result;
}

////////////////////////////////////////////////////////////
//~ Align reader

// Align the pos to the next byte
void BB_ReadAlignToNextByte(BB_Reader *bbr)
{
#if BITBUFF_DEBUG
  if ((bbr->cur_bit & 7) != 0)
  {
    BB_ReadDebugMagic(bbr, BB_DebugMagicKind_AlignNextByte, 0);
  }
#endif
  bbr->cur_bit += (8 - (bbr->cur_bit & 7)) & 7;
}

void BB_ReadAlignBytes(BB_Reader *bbr, u64 align)
{
  BB_ReadAlignToNextByte(bbr);
  BB_ReadDebugMagic(bbr, BB_DebugMagicKind_AlignBytes, align);
  if (align > 0)
  {
    u64 new_pos = (bbr->cur_bit >> 3);
    new_pos += (align - 1);
    new_pos -= new_pos % align;
    if (BB_CheckReaderOverflowBits(bbr, (new_pos << 3) - bbr->cur_bit))
    {
      return;
    }
    bbr->cur_bit = new_pos << 3;
  }
}

////////////////////////////////////////////////////////////
//~ Read bits

u64 BB_ReadUBitsNoMagic(BB_Reader *bbr, u8 num_bits)
{
  if (BB_CheckReaderOverflowBits(bbr, num_bits))
  {
    return 0;
  }

  u64 result = 0;

  u8 offset = bbr->cur_bit & 7;
  u8 num_trailing_bits = 0;
  if (offset)
  {
    u8 *at = bbr->base + (bbr->cur_bit >> 3);
    num_trailing_bits = MinU8(8 - offset, num_bits);
    u8 mix_byte = *at;
    mix_byte >>= offset;
    mix_byte &= (1 << num_trailing_bits) - 1;
    result = mix_byte;
    num_bits -= num_trailing_bits;
    bbr->cur_bit += num_trailing_bits;
  }

  // cur_bit is now aligned to byte
  u8 *at = bbr->base + (bbr->cur_bit >> 3);
  u8 num_bytes = (num_bits + 7) >> 3;
  u64 tmp = 0;
  CopyBytes(&tmp, at, num_bytes);
  u64 mask = U64Max;
  if (num_bits < 64)
  {
    mask = ~(U64Max << num_bits);
  }
  tmp &= mask;
  result |= tmp << num_trailing_bits;
  bbr->cur_bit += num_bits;
  return result;
}

u64 BB_ReadUBits(BB_Reader *bbr, u8 num_bits)
{
  BB_ReadDebugMagic(bbr, BB_DebugMagicKind_UBits, num_bits);
  return BB_ReadUBitsNoMagic(bbr, num_bits);
}

i64 BB_ReadIBits(BB_Reader *bbr, u8 num_bits)
{
  Assert(num_bits > 1);
  BB_ReadDebugMagic(bbr, BB_DebugMagicKind_IBits, num_bits);
  u64 tc = BB_ReadUBits(bbr, num_bits);
  return BB_IntFromTwosCompliment(tc, num_bits);
}

u8 BB_ReadBit(BB_Reader *bbr)
{
  return BB_ReadUBits(bbr, 1);
}

////////////////////////////////////////////////////////////
//~ Read variable length integer

// Read a variable length unsigned integer.
// See BB_WriteUV for details.
u64 BB_ReadUV(BB_Reader *bbr)
{
  BB_ReadDebugMagic(bbr, BB_DebugMagicKind_UV, 0);

  u64 result = 0;
  for (u64 i = 0; i <= 9; ++i)
  {
    u64 part = BB_ReadUBits(bbr, 8);
    u8 is_last_part = part <= 0x7F;
    result |= (part & 0x7F) << (i * 7);
    if (is_last_part)
    {
      break;
    }
  }
  return result;
}

// Read a variable length signed integer.
// See BB_WriteIV for details.
i64 BB_ReadIV(BB_Reader *bbr)
{
  BB_ReadDebugMagic(bbr, BB_DebugMagicKind_IV, 0);
  u8 first_byte = BB_ReadUBits(bbr, 8);
  u8 cont_bit = first_byte & 0x80;
  u8 sign_bit = first_byte & 0x40;

  u8 num_bits = 6;
  u64 tc = first_byte & 0x3F;
  if (cont_bit)
  {
    for (u64 i = 0; i <= 9; ++i)
    {
      u64 part = BB_ReadUBits(bbr, 8);
      u8 is_last_part = part <= 0x7F;
      tc |= (part & 0x7F) << num_bits;
      num_bits += 7;
      if (is_last_part)
      {
        break;
      }
    }
  }
  num_bits = MinU8(num_bits, 64);

  i64 result;
  if (sign_bit)
  {
    // Sign bit is 1, indicating result is stored in twos compliment
    result = BB_IntFromTwosCompliment(tc, num_bits);
  }
  else
  {
    result = (i64)tc;
  }

  return result;
}

////////////////////////////////////////////////////////////
//~ Read floating point

f32 BB_ReadF32(BB_Reader *bbr)
{
  BB_ReadDebugMagic(bbr, BB_DebugMagicKind_F32, 0);
  u32 ubits = BB_ReadUBits(bbr, 32);
  return *(f32 *)&ubits;
}

f64 BB_ReadF64(BB_Reader *bbr)
{
  BB_ReadDebugMagic(bbr, BB_DebugMagicKind_F64, 0);
  u64 ubits = BB_ReadUBits(bbr, 64);
  return *(f64 *)&ubits;
}

////////////////////////////////////////////////////////////
//~ Read Uid

Uid BB_ReadUid(BB_Reader *bbr)
{
  BB_ReadDebugMagic(bbr, BB_DebugMagicKind_Uid, 128);
  u64 hi = BB_ReadUBits(bbr, 64);
  u64 lo = BB_ReadUBits(bbr, 64);
  return UID(hi, lo);
}

////////////////////////////////////////////////////////////
//~ Read raw data

String BB_ReadString(Arena *arena, BB_Reader *bbr)
{
  BB_ReadDebugMagic(bbr, BB_DebugMagicKind_String, 0);
  String result = Zi;
  u64 len = BB_ReadUV(bbr);
  u8 *src = BB_ReadBytesRaw(bbr, len);
  if (src != 0)
  {
    result.len = len;
    result.text = PushStructsNoZero(arena, u8, len);
    CopyBytes(result.text, src, len);
  }
  return result;
}

String BB_ReadStringRaw(BB_Reader *bbr)
{
  BB_ReadDebugMagic(bbr, BB_DebugMagicKind_String, 0);
  String result = Zi;
  u64 len = BB_ReadUV(bbr);
  u8 *src = BB_ReadBytesRaw(bbr, len);
  if (src != 0)
  {
    result.len = len;
    result.text = src;
  }
  return result;
}

// Will fill dst with zeroes if bitbuff overflows
void BB_ReadBytes(BB_Reader *bbr, String out)
{
  u8 *src = BB_ReadBytesRaw(bbr, out.len);
  if (src)
  {
    CopyBytes(out.text, src, out.len);
  }
  else
  {
    ZeroBytes(out.text, out.len);
  }
}

// Will return 0 on bitbuff overflow. Result should be checked.
u8 *BB_ReadBytesRaw(BB_Reader *bbr, u64 num_bytes)
{
  BB_ReadAlignToNextByte(bbr);

  u64 num_bits = num_bytes << 3;
  if (BB_CheckReaderOverflowBits(bbr, num_bits))
  {
    return 0;
  }

  u8 *raw = bbr->base + (bbr->cur_bit >> 3);
  bbr->cur_bit += num_bits;

  return raw;
}

void BB_ReadSeekBytes(BB_Reader *bbr, u64 num_bytes)
{
  BB_ReadAlignToNextByte(bbr);

  u64 num_bits = num_bytes << 3;
  if (BB_CheckReaderOverflowBits(bbr, num_bits))
  {
    return;
  }

  bbr->cur_bit += num_bits;
}

void BB_ReadSeekToByte(BB_Reader *bbr, u64 pos)
{
  u64 cur_byte_pos = bbr->cur_bit >> 3;
  if (pos >= cur_byte_pos)
  {
    BB_ReadSeekBytes(bbr, pos - cur_byte_pos);
  }
  else
  {
    // Tried to seek byte backwards in reader
    Assert(0);
    bbr->overflowed = 1;
    bbr->cur_bit = (bbr->base_len << 3);
  }
}

////////////////////////////////////////////////////////////
//~ Reader debug

#if BITBUFF_DEBUG

void BB_ReadDebugMagic(BB_Reader *bbr, BB_DebugMagicKind expected_magic, u8 expected_num_bits)
{
  if (bbr->debug_enabled)
  {
    if (BB_CheckReaderOverflowBits(bbr, 24))
    {
      return;
    }
    u64 stored = BB_ReadUBitsNoMagic(bbr, 24);
    BB_DebugMagicKind stored_magic = stored & 0xFFFF;
    u8 stored_num_bits = (stored >> 16) & 0xFF;

    // Verify stored magic match
    Assert(expected_magic == stored_magic);

    // Verify stored bit count match
    Assert(expected_num_bits == stored_num_bits);
  }
}

void BB_ReadDebugMarker(BB_Reader *bbr, String name)
{
  bbr->cur_bit += (8 - (bbr->cur_bit & 7)) & 7;
  for (u64 i = 0; i < name.len; ++i)
  {
    u8 c_stored = BB_ReadUBitsNoMagic(bbr, 8);
    u8 c_expected = name.text[i];
    Assert(c_expected == c_stored);
  }
}

#endif

////////////////////////////////////////////////////////////
//~ Utils

u64 BB_TwosComplimentFromUint(u64 value, u8 num_bits)
{
  u64 mask = U64Max;
  if (num_bits < 64)
  {
    mask = ~(U64Max << num_bits);
  }
  u64 tc = (~value & mask) + 1;
  tc &= mask;
  return tc;
}

i64 BB_IntFromTwosCompliment(u64 tc, u8 num_bits)
{
  u64 msb_mask = (u64)1 << (num_bits - 1);
  i64 value = -(i64)(tc & msb_mask);
  value += tc & ~msb_mask;
  return value;
}

////////////////////////////////////////////////////////////
//~ Test

void BB_Test(void)
{
  TempArena scratch = BeginScratchNoConflict();

  u8 kind_ubits = 0;
  u8 kind_ibits = 1;
  u8 kind_uv = 2;
  u8 kind_iv = 3;
  u8 kind_string = 4;

  struct test_case_ubits { u64 v; u64 num_bits; };
  struct test_case_ibits { i64 v; u64 num_bits; };
  struct test_case_uv { u64 v; };
  struct test_case_iv { i64 v; };
  struct test_case_string { String v; };
  struct test_case
  {
    u8 kind;
    union
    {
      struct test_case_ubits ubits;
      struct test_case_ibits ibits;
      struct test_case_uv uv;
      struct test_case_iv iv;
      struct test_case_string s;
    };
  };

  struct test_case cases[] = {
    { kind_ubits, .ubits = { 40, 8 } },
    { kind_ubits, .ubits = { 32, 8 } },
    { kind_ubits, .ubits = { 100, 7 } },
    { kind_ubits, .ubits = { 4, 3 } },
    { kind_ubits, .ubits = { 13, 8 } },

    { kind_ibits, .ibits = { 0, 8 } },
    { kind_ibits, .ibits = { -1, 8 } },
    { kind_ibits, .ibits = { -2, 8 } },
    { kind_ibits, .ibits = { -3, 8 } },
    { kind_ibits, .ibits = { -100, 8 } },
    { kind_ibits, .ibits = { -50, 7 } },
    { kind_ibits, .ibits = { 50, 7 } },
    { kind_ibits, .ibits = { 4, 7 } },
    { kind_ibits, .ibits = { 1, 7 } },
    { kind_ibits, .ibits = { 3, 3 } },
    { kind_ibits, .ibits = { 1, 2 } },
    { kind_ibits, .ibits = { 0, 2 } },
    { kind_ibits, .ibits = { -1, 2 } },

    { kind_uv, .uv = { 0 } },
    { kind_uv, .uv = { 100 } },
    { kind_uv, .uv = { 10000 } },
    { kind_uv, .uv = { 10000000000000 } },
    { kind_uv, .uv = { U64Max } },

    { kind_iv, .iv = { 0 } },
    { kind_iv, .iv = { -1 } },
    { kind_iv, .iv = { 10000000000000 } },
    { kind_iv, .iv = { -10000000000000 } },
    { kind_iv, .iv = { I64Max } },
    { kind_iv, .iv = { I64Min } },

    { kind_string, .s = { Lit("Hello there! Hope you're doing well.") } },
    { kind_ibits, .ibits = { 3, 3 } },
    { kind_string, .s = { Lit("Alriiiiiiiiiiiiiiiiiiighty then") } },
    { kind_string, .s = { Lit("Alriiiiiiiiiiiiiiiiiiighty then") } },
  };

  String encoded = Zi;
  {
    BB_Buff bb = BB_AcquireDynamicBuff(Gibi(64));
    BB_Writer bbw = BB_WriterFromBuff(&bb);
    for (u64 i = 0; i < countof(cases); ++i)
    {
      struct test_case c = cases[i];
      if (c.kind == kind_ubits)
      {
        BB_WriteUBits(&bbw, c.ubits.v, c.ubits.num_bits);
      }
      else if (c.kind == kind_ibits)
      {
        BB_WriteIBits(&bbw, c.ibits.v, c.ibits.num_bits);
      }
      else if (c.kind == kind_uv)
      {
        BB_WriteUV(&bbw, c.uv.v);
      }
      else if (c.kind == kind_iv)
      {
        BB_WriteIV(&bbw, c.iv.v);
      }
      else if (c.kind == kind_string)
      {
        BB_WriteString(&bbw, c.s.v);
      }
      else
      {
        Assert(0);
      }
    }
    encoded = BB_GetWritten(scratch.arena, &bbw);
  }

  {
    BB_Buff bb = BB_BuffFromString(encoded);
    BB_Reader bbr = BB_ReaderFromBuff(&bb);
    for (u64 i = 0; i < countof(cases); ++i)
    {
      struct test_case c = cases[i];
      if (c.kind == kind_ubits)
      {
        u64 w = c.ubits.v;
        u64 r = BB_ReadUBits(&bbr, c.ubits.num_bits);
        Assert(r == w);
      }
      else if (c.kind == kind_ibits)
      {
        i64 w = c.ibits.v;
        i64 r = BB_ReadIBits(&bbr, c.ubits.num_bits);
        Assert(r == w);
      }
      else if (c.kind == kind_uv)
      {
        u64 w = c.uv.v;
        u64 r = BB_ReadUV(&bbr);
        Assert(r == w);
      }
      else if (c.kind == kind_iv)
      {
        i64 w = c.iv.v;
        i64 r = BB_ReadIV(&bbr);
        Assert(r == w);
      }
      else if (c.kind == kind_string)
      {
        String w = c.s.v;
        String r = BB_ReadString(scratch.arena, &bbr);
        Assert(MatchString(r, w));
      }
      else
      {
        Assert(0);
      }
    }
  }

  EndScratch(scratch);
}