12.10 __qsub8 intrinsic

This intrinsic inserts a QSUB8 instruction into the instruction stream generated by the compiler.

It enables you to perform four 8-bit integer subtractions, saturating the results to the 8-bit signed integer range -27 ≤ x ≤ 27 - 1.

Syntax

unsigned int __qsub8(unsigned int val1, unsigned int val2)
Where:
val1
holds the first four 8-bit operands
val2
holds the second four 8-bit operands.

Return value

The __qsub8 intrinsic returns:
  • The subtraction of the first byte in the second operand from the first byte in the first operand, in the first byte of the return value.
  • The subtraction of the second byte in the second operand from the second byte in the first operand, in the second byte of the return value.
  • The subtraction of the third byte in the second operand from the third byte in the first operand, in the third byte of the return value.
  • The subtraction of the fourth byte in the second operand from the fourth byte in the first operand, in the fourth byte of the return value.
The returned results are saturated to the 8-bit signed integer range -27 x ≤ 27 - 1.

Examples

unsigned int subtract_bytes(unsigned int val1, unsigned int val2)
{
    unsigned int res;
    res = __qsub8(val1,val2); /* res[7:0] = val1[7:0] - val2[7:0]
                                 res[15:8] = val1[15:8] - val2[15:8]
                                 res[23:16] = val1[23:16] - val2[23:16]
                                 res[31:24] = val1[31:24] - val2[31:24]
                               */
    return res;
}
Related reference
9.143 ARMv6 SIMD intrinsics
Related information
QSUB8
Saturating instructions
ARM and Thumb instruction summary
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