12.23 __smlald intrinsic

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

It enables you to 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.

Syntax

unsigned long long __smlald(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 __smlald intrinsic returns the product of each multiplication added to the accumulate value.

Examples

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[15:0]
                                       p2 = val1[31:16] × val2[31:16]
                                       sum = p1 + p2 + val3[63:32][31:0]
                                       res[63:32] = sum[63:32]
                                       res[31:0] = sum[31:0]
                                     */
    return res;
}
Related reference
10.147 ARMv6 SIMD intrinsics
Related information
SMLALD
ARM and Thumb instruction summary
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