RealView Compilation Tools - ARM Information Center

Compiler-specific Features
4.7.52 __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 -2 15 ≤ x ≤ 2 15 - 1.
unsigned int __qasx(unsigned int val1, unsigned int val2)
Where:
val1
val2
holds the first operand for the subtraction in the low halfword, and the
first operand for the addition in the high halfword
holds the second operand for the subtraction in the high halfword, and the
second operand for the addition in the low halfword.
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 -2 15 ≤ x ≤ 2 15 - 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;
See also
• ARMv6 SIMD intrinsics on page 4-109
• Instruction summary on page 4-2 in the Assembler Guide
• Saturating instructions on page 4-93 in the Assembler Guide
4-124 Copyright © 2007-2010 ARM. All rights reserved. ARM DUI 0348C
Non-Confidential,
ID101213