  We present an accelerated and hardware parallelized integral-equation solver
for the problem of acoustic scattering by a two-dimensional surface in
three-dimensional space. The approach is based, in part, on the novel
Interpolated Factored Green Function acceleration method (IFGF) that, without
recourse to the Fast Fourier Transform (FFT), evaluates the action of Green
function-based integral operators for an $N$-point surface discretization at a
complexity of $\Ord(N\log N)$ operations instead of the $\Ord(N^2)$ cost
associated with nonaccelerated methods. The IFGF algorithm exploits the slow
variations of factored Green functions to enable the fast evaluation of fields
generated by groups of sources on the basis of a recursive interpolation
scheme. In the proposed approach, the IFGF method is used to account for the
vast majority of the computations, while, for the relatively few singular,
nearly-singular and neighboring non-singular integral operator evaluations, a
high-order rectangular-polar quadrature approach is employed instead. Since the
overall approach does not rely on the FFT, it is amenable to efficient shared-
and distributed-memory parallelization; this paper demonstrates such a
capability by means of an OpenMP parallel implementation of the method. A
variety of numerical examples presented in this paper demonstrate that the
proposed methods enable the efficient solution of large problems over complex
geometries on small parallel hardware infrastructures. Numerical examples
include acoustic scattering by a sphere of up to $128$ wavelengths, an
$80$-wavelength submarine, and a turbofan nacelle that is more than $80$
wavelengths in size, requiring, on a 28-core computer, computing times of the
order of a few minutes per iteration and a few tens of iterations of the GMRES
iterative solver.
