This intrinsic inserts a VFP
into the instruction stream generated by the compiler. It enables
you to obtain the square root of a double-precision floating-point
value from within your C or C++ code.
__sqrt intrinsic is an analogue of
the standard C library function
sqrt. It differs
from the standard library function in that a call to
guaranteed to be compiled into a single, inline, machine instruction
on an ARM architecture-based processor equipped with a VFP coprocessor.