12.25 __smlsd intrinsic

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

It enables you to perform two 16-bit signed multiplications, take the difference of the products, subtracting the high halfword product from the low halfword product, and add the difference to a 32-bit accumulate operand. The Q bit is set if the accumulation overflows. Overflow cannot occur during the multiplications or the subtraction.

Syntax

unsigned int __smlsd(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.

Examples

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[15:0]
                                      p2 = val1[31:16] × val2[31:16]
                                      res[31:0] = p1 - p2 + val3[31:0]
                                    */
    return res;
}
Related reference
9.143 ARMv6 SIMD intrinsics
Related information
SMLSD
ARM and Thumb instruction summary
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