12.58 __usub16 intrinsic

This intrinsic inserts a USUB16 instruction into the instruction stream generated by the compiler.

It enables you to perform two 16-bit unsigned integer subtractions.

The GE bits in the APSR are set according to the results.

Syntax

unsigned int __usub16(unsigned int val1, unsigned int val2)

Where:

val1

holds the first two halfword operands

val2

holds the second two halfword operands.

Return value

The __usub16 intrinsic returns:

  • The subtraction of the low halfword in the second operand from the low halfword in the first operand, in the low halfword of the return value.

  • The subtraction of the high halfword in the second operand from the high halfword in the first operand, in the high halfword of the return value.

Each bit in APSR.GE is set or cleared for each byte in the return value, depending on the results of the operation. If res is the return value, then:

  • If res[15:0] ≥ 0 then APSR.GE[1:0] = 11 else 00.

  • If res[31:16] ≥ 0 then APSR.GE[3:2] = 11 else 00.

Examples

unsigned int subtract_halfwords(unsigned int val1, unsigned int val2)
{
    unsigned int res;
    res = __usub16(val1,val2); /* res[15:0] = val1[15:0] - val2[15:0]
                                  res[31:16] = val1[31:16] - val2[31:16]
                                */    
    return res;
}
Related reference
10.147 ARMv6 SIMD intrinsics
Related information
USUB16
ARM and Thumb instruction summary
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