UTF-16 sandbox (decode)

Step-by-step breakdown

1. 01

   Given endianness

   Each code unit is read low-order byte first (Little Endian).

   Little Endian (LE)
2. 02

   Identify the code unit count

   4 bytes = surrogate pair for a code point beyond the BMP. The high code unit is in 0xD800 → 0xDBFF, the low one in 0xDC00 → 0xDFFF.

   2 code units · surrogate pair
3. 03

   Extract the useful bits from each surrogate

   Subtract 0xD800 from the high surrogate (10 high bits) and 0xDC00 from the low surrogate (10 low bits).

   0000111100 | 1110001001
4. 04

   Reassemble the binary

   Concatenate the 10 + 10 bits then add 0x10000 to recover the code point.

   00001111001110001001
5. 05

   Convert to a code point

   The binary equals 127881 in decimal, i.e. U+1F389 in Unicode notation.

   U+1F389