Description #Description

Encoding of a single character from an ISO 10646 character value to UTF-16 proceeds as follows. Let U be the character number, no greater than 0x10FFFF.

1) If U < 0x10000, encode U as a 16-bit unsigned integer and terminate.

2) Let U’ = U – 0x10000. Because U is less than or equal to 0x10FFFF, U’ must be less than or equal to 0xFFFFF. That is, U’ can be represented in 20 bits.

3) Initialize two 16-bit unsigned integers, W1 and W2, to 0xD800 and 0xDC00, respectively. These integers each have 10 bits free to encode the character value, for a total of 20 bits.

4) Assign the 10 high-order bits of the 20-bit U’ to the 10 low-order bits of W1 and the 10 low-order bits of U’ to the 10 low-order bits of W2. Terminate.

Graphically, steps 2 through 4 look like: U’ = yyyyyyyyyyxxxxxxxxxx W1 = 110110yyyyyyyyyy W2 = 110111xxxxxxxxxx