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# `__usada8 `intrinsic

This intrinsic inserts a `USADA8 `instruction into the instruction stream generated by the compiler. It enables you to perform four unsigned 8-bit subtractions, and add the absolute values of the differences to a 32-bit accumulate operand.

```unsigned int __usada8(unsigned int `val1`, unsigned int `val2`, unsigned int `val3`)
```

Where:

`val1`

holds the first four 8-bit operands for the subtractions

`val2`

holds the second four 8-bit operands for the subtractions

`val3`

holds the accumulation value.

The `__usada8 `intrinsic returns the sum of the absolute differences of the following bytes, added to the accumulation value:

• the subtraction of the first byte in the second operand from the first byte in the first operand

• the subtraction of the second byte in the second operand from the second byte in the first operand

• the subtraction of the third byte in the second operand from the third byte in the first operand

• the subtraction of the fourth byte in the second operand from the fourth byte in the first operand.

Example:

```unsigned int subtract_add_diff_accumulate(unsigned int val1, unsigned int val2, unsigned int val3)
{
unsigned int res;

res = __usada8(val1,val2,val3); /* absdiff1 = val1[7:0] - val2[7:0]
absdiff2 = val1[15:8] - val2[15:8]
absdiff3 = val1[23:16] - val2[23:16]
absdiff4 = val1[31:24] - val2[31:24]
sum = absdiff1 + absdiff2 + absdiff3
+ absdiff4
res[31:0] = sum[31:0] + val3[31:0]
*/
return res;
}
```