This intrinsic inserts an SMLALDX instruction into the instruction stream generated by the compiler. It enables you to exchange the halfwords of the second operand, and perform two signed 16-bit multiplications, adding both results to a 64-bit accumulate operand. Overflow is only possible as a result of the 64-bit addition. This overflow is not detected if it occurs. Instead, the result wraps around modulo 2⁶⁴.

unsigned long long__smlaldx(unsigned int val1, unsigned int val2, unsigned long long val3)

Where:

The __smlald intrinsic returns the product of each multiplication added to the accumulate value.

Example:

unsigned int dual_multiply_accumulate(unsigned int val1, unsigned int val2, unsigned int val3)
{
  unsigned int res;

    res = __smlald(val1,val2,val3); /* p1 = val1[15:0] × val2[31:16]
                                       p2 = val1[31:16] × val2[15:0]
                                       sum = p1 + p2 + val3[63:32][31:0]
                                       res[63:32] = sum[63:32]
                                       res[31:0] = sum[31:0]
                                     */
    return res;
}