关于SimpleMsgPack中swap引发的问题大端法和小端法研究笔记

Float format family stores a floating point number in 5 bytes or 9 bytes.
float 32 stores a floating point number in IEEE 754 single precision floating point number format:
+--------+--------+--------+--------+--------+
|  0xca  |XXXXXXXX|XXXXXXXX|XXXXXXXX|XXXXXXXX
+--------+--------+--------+--------+--------+

float 64 stores a floating point number in IEEE 754 double precision floating point number format:
+--------+--------+--------+--------+--------+--------+--------+--------+--------+
|  0xcb  |YYYYYYYY|YYYYYYYY|YYYYYYYY|YYYYYYYY|YYYYYYYY|YYYYYYYY|YYYYYYYY|YYYYYYYY|
+--------+--------+--------+--------+--------+--------+--------+--------+--------+
where
* XXXXXXXX_XXXXXXXX_XXXXXXXX_XXXXXXXX is a big-endian IEEE 754 single precision floating point number
* YYYYYYYY_YYYYYYYY_YYYYYYYY_YYYYYYYY_YYYYYYYY_YYYYYYYY_YYYYYYYY_YYYYYYYY is a big-endian
  IEEE 754 double precision floating point number

procedure swap64Ex(const v; out outVal);
begin
  // 7F F5 B8 6F B5 0E 04 40

  // 40 04 0E B5 6F B8 F5 7F
  PByte(@outVal)^ := PByte(IntPtr(@v) + 7)^;
  PByte(IntPtr(@outVal) + 1)^ := PByte(IntPtr(@v) + 6)^;
  PByte(IntPtr(@outVal) + 2)^ := PByte(IntPtr(@v) + 5)^;
  PByte(IntPtr(@outVal) + 3)^ := PByte(IntPtr(@v) + 4)^;
  PByte(IntPtr(@outVal) + 4)^ := PByte(IntPtr(@v) + 3)^;
  PByte(IntPtr(@outVal) + 5)^ := PByte(IntPtr(@v) + 2)^;
  PByte(IntPtr(@outVal) + 6)^ := PByte(IntPtr(@v) + 1)^;
  PByte(IntPtr(@outVal) + 7)^ := PByte(@v)^;
end;

function swap(v:Double): Double; overload;
begin
  swap64Ex(v, Result);
end;

function swap(v:Double): Int64; overload;
begin
  swap64Ex(v, Result);
end;