Added fast parallel interpolator. Some adjustment to BORG icgen

python/_fast_interp.pyx

@@ -0,0 +1,32 @@
+from cpython cimport bool
+from cython cimport view
+from cython.parallel import prange, parallel
+from libc.math cimport sin, cos, abs, floor, round, sqrt
+import numpy as np
+cimport numpy as npx
+cimport cython
+
+__all__=["fast_interp"]
+
+
+@cython.boundscheck(False)
+@cython.cdivision(True)
+def fast_interp(npx.float64_t xmin, npx.float64_t dx, npx.float64_t[:] A, npx.float64_t[:] y, npx.float64_t[:] out, npx.float64_t beyond_val=npx.nan):
+  cdef double rq, q
+  cdef int iq
+  cdef long i, Asize, ysize
+  cdef npx.float64_t[:] out0
+
+  ysize = y.size
+  out0 = out
+  Asize = A.size
+
+  with nogil:
+    for i in prange(ysize):
+      q = (y[i] - xmin) / dx
+      iq = int(floor(q))
+      rq = (q-iq)
+      if iq+1 >= Asize or iq < 0:
+        out0[i] = beyond_val
+      else:
+        out0[i] = rq * A[iq+1] + (1-rq)*A[iq]