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Compiler-specific Features
4.7.53 __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 -2 15 ≤ x ≤ 2 15 - 1.
unsigned int __qsax(unsigned int val1, unsigned int val2)
Where:
val1
val2
holds the first operand for the addition in the low halfword, and the first
operand for the subtraction in the high halfword
holds the second operand for the addition in the high halfword, and the
second operand for the subtraction in the low halfword.
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 -2 15 ≤ x ≤ 2 15 - 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;
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
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