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Compiler-specific Features
4.7.99 __usad8 intrinsic
This intrinsic inserts a USAD8 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 together, returning the result as a single unsigned
integer.
unsigned int __usad8(unsigned int val1, unsigned int val2)
Where:
val1
val2
holds the first four 8-bit operands for the subtractions
holds the second four 8-bit operands for the subtractions.
The __usad8 intrinsic returns the sum of the absolute differences of:
• 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.
The sum is returned as a single unsigned integer.
Example:
unsigned int subtract_add_abs(unsigned int val1, unsigned int val2)
{
unsigned int res;
}
res = __usad8(val1,val2); /* 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]
res[31:0] = absdiff1 + absdiff2 + absdiff3
+ absdiff4
*/
return res;
See also
• ARMv6 SIMD intrinsics on page 4-109
• Instruction summary on page 4-2 in the Assembler Guide
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