12.20 __shsub8 intrinsic

This intrinsic inserts a SHSUB8 instruction into the instruction stream generated by the compiler.

It enables you to perform four signed 8-bit integer subtractions, halving the results.

Syntax

unsigned int __shsub8(unsigned int val1, unsigned int val2)
Where:
val1
holds the first four operands
val2
holds the second four operands.

Return value

The __shsub8 intrinsic returns:
  • The halved 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 halved 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 halved 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 halved 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.

Examples

unsigned int subtract_and_halve(unsigned int val1, unsigned int val2)
{
    unsigned int res;
    res = __shsub8(val1,val2); /* res[7:0] = (val1[7:0] - val2[7:0]) >> 1
                                  res[15:8] = (val1[15:8] - val2[15:8]) >> 1
                                  res[23:16] = (val1[23:16] - val2[23:16] >> 1
                                  res[31:24] = (val1[31:24] - val2[31:24] >> 1
                                */
    return res;
}
Related reference
9.143 ARMv6 SIMD intrinsics
Related information
SHSUB8
ARM and Thumb instruction summary
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