12.24 __smlaldx intrinsic

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)
holds the first halfword operands for each multiplication
holds the second halfword operands for each multiplication
holds the accumulate value.

Return value

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


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;
Related reference
9.143 ARMv6 SIMD intrinsics
Related information
ARM and Thumb instruction summary
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