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__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.

unsigned int __shsub8(unsigned int val1, unsigned int val2)

Where:

val1

holds the first four operands

val2

holds the second four operands.

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

Example:

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;
}

See also

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