int16x2 __sxtb16(int8x4 val);

**__sxtb16** inserts a SXTB16 instruction. **__sxtb16** returns the 16-bit signed equivalent of

- res[0] = (short)val[0]
- res[1] = (short)val[2]

where res[0] is the lower 16 bits, res[1] is the upper 16 bits, val[0] is the lower 8 bits and val[2] is the 8 bits starting at bit position 16.