12.8 __qsax intrinsic

This intrinsic inserts a QSAX instruction into the instruction stream generated by the compiler.

It enables you to exchange the halfwords of one operand, then subtract the high halfwords and add the low halfwords, saturating the results to the 16-bit signed integer range -215 ≤ x ≤ 215 - 1.

Syntax

unsigned int __qsax(unsigned int val1, unsigned int val2)
Where:
val1
holds the first operand for the addition in the low halfword, and the first operand for the subtraction in the high halfword
val2
holds the second operand for the addition in the high halfword, and the second operand for the subtraction in the low halfword.

Return value

The __qsax intrinsic returns:
  • The saturated addition of the low halfword of the first operand and the high halfword of the second operand, in the low halfword of the return value.
  • The saturated subtraction of the low halfword of the second operand from the high halfword of the first operand, in the high halfword of the return value.
The returned results are saturated to the 16-bit signed integer range -215 ≤ x ≤ 215 - 1.

Example

unsigned int exchange_subtract_and_add(unsigned int val1, unsigned int val2)
{
    unsigned int res;
    res = __qsax(val1,val2); /* res[15:0] = val1[15:0] + val2[31:16]
                                res[31:16] = val1[31:16] - val2[15:0]
                              */
                             /* Alternative equivalent representation:
                                val2[15:0][31:16] = val2[31:16][15:0]
                                res[15:0] = val1[15:0] + val2[15:0]
                                res[31:16] = val[31:16] - val2[31:16]
                              */
    return res;
}
Related reference
9.144 ARMv6 SIMD intrinsics
Related information
QSAX
Saturating instructions
ARM and Thumb instruction summary
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