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Compiler-specific Features
4.7.103 __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.
unsigned int __usub16(unsigned int val1, unsigned int val2)
Where:
val1
val2
holds the first two halfword operands
holds the second two halfword operands.
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.
Example:
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]
*/
See also
• ARMv6 SIMD intrinsics on page 4-109
• Instruction summary on page 4-2 in the Assembler Guide
• Parallel add and subtract on page 4-99 in the Assembler Guide.
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