12.7 __qasx intrinsic

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

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

Syntax

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

Return value

The __qasx intrinsic returns:
  • The saturated subtraction of the high halfword in the second operand from the low halfword in the first operand, in the low halfword of the return value.
  • The saturated addition of the high halfword in the first operand and the low halfword in the second 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_add_and_subtract(unsigned int val1, unsigned int val2)
{
    unsigned int res;
    res = __qasx(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
QASX
Saturating instructions
ARM and Thumb instruction summary
Non-ConfidentialPDF file icon PDF versionARM DUI0375F
Copyright © 2007, 2008, 2011, 2012, 2014 ARM. All rights reserved.