Type    Name    Description
uint32  scaler type     A tag to indicate the OFA scaler to be used to rasterize this font; see the note on the scaler type below for more information.
uint16  numTables   number of tables
uint16  searchRange     (maximum power of 2 <= numTables)*16
uint16  entrySelector   log2(maximum power of 2 <= numTables)
uint16  rangeShift  numTables*16-searchRange

struct Offset_Subtable;
{
    uint32 scaler_type_;
    uint16 numTables_;
    uint16 searchRange_;
    uint16 entrySelector_;
    uint16 rangeShift_;

    bool is_for_macOS() { return scaler_type_ == 0x74727565; }
    bool is_for_windoes() { return scaler_type_ == 0x00010000; }
    bool is_truetype() { return scaler_type_ == 0x74727565 ||
                         scaler_type_ == 0x00010000; }
    bool is_postscript() { return scaler_type_ == 0x74797031; }
};

Type    Name    Description
uint32  tag     4-byte identifier
uint32  checkSum    checksum for this table
uint32  offset  offset from beginning of sfnt
uint32  length  length of this table in byte (actual length not padded length)

struct Table_Directory_Entry
{
    uint32 tag_;
    uint32 checkSum_;
    uint32 offset_;
    uint32 length_;
};

const void* p_ttf = ...;
const Offset_Subtable* p_os = static_cast<const Offset_Subtable*>(p_ttf);
... use any data you're interested in...
for (int table_num = 1; table_num <= p_os->numTables_; ++table_num)
{
    const Table_Directory_Entry* p_tde =
        reinterpret_cast<const Table_Directory_Entry*>(&p_os[1]);
    ... use the table directory entry data ...
}