12.26 __smlsdx intrinsic

This intrinsic inserts an SMLSDX instruction into the instruction stream generated by the compiler.

It enables you to exchange the halfwords in the second operand, then perform two 16-bit signed multiplications. The difference of the products is added to a 32-bit accumulate operand. The Q bit is set if the addition overflows. Overflow cannot occur during the multiplications or the subtraction.

Syntax

unsigned int __smlsdx(unsigned int val1, unsigned int val2, unsigned int val3)
Where:
val1
holds the first halfword operands for each multiplication
val2
holds the second halfword operands for each multiplication
val3
holds the accumulate value.

Return value

The __smlsd intrinsic returns the difference of the product of each multiplication, added to the accumulate value.

Example

unsigned int dual_multiply_diff_prods(unsigned int val1, unsigned int val2, unsigned int val3)
{
    unsigned int res;
    res = __smlsd(val1,val2,val3); /* p1 = val1[15:0] × val2[31:16]
                                      p2 = val1[31:16] × val2[15:0]
                                      res[31:0] = p1 - p2 + val3[31:0]
                                    */
    return res;
}
Related reference
9.144 ARMv6 SIMD intrinsics
Related information
SMLSDX
ARM and Thumb instruction summary
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