12.27 __smlsld intrinsic

This intrinsic inserts an SMLSLD 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 64-bit accumulate operand. Overflow cannot occur during the multiplications or the subtraction. Overflow can occur as a result of the 64-bit addition, and this overflow is not detected. Instead, the result wraps round to modulo 264.

Syntax

unsigned long long __smlsld(unsigned int val1, unsigned int val2, unsigned long long 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 __smlsld intrinsic returns the difference of the product of each multiplication, added to the accumulate value.

Examples

unsigned long long dual_multiply_diff_prods(unsigned int val1, unsigned int val2, unsigned long long val3)
{
    unsigned int res;
    res = __smlsld(val1,val2,val3); /* p1 = val1[15:0] × val2[15:0]
                                       p2 = val1[31:16] × val2[31:16]
                                       res[63:0] = p1 - p2 + val3[63:0]
                                     */
    return res;
}
Related reference
10.147 ARMv6 SIMD intrinsics
Related information
SMLSLD
ARM and Thumb instruction summary
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