int16x2 __sxtab16(int16x2 val1, uint8x4 val2);

**__sxtab16** inserts a SXTAB16 instruction. **__sxtab16** returns the 16-bit signed equivalent of

- res[0] = val1[0] + (short)val2[0]
- res[1] = val1[1] + (short)val2[2]

where res[0] & val1[0] are the lower 16 bits, res[1] & val1[1] are the upper 16 bits, val2[0] is the lower 8 bits and val2[2] is the 8 bits starting at bit position 16.