feat(tools): add tools for handling frequency maps.

Adds a tool to match the shuffle, crate, slot, link values to each
frequecy bin based on a frequency map. Also adds a function to get a
default stream.

ch_util/tools.py

@@ -121,6 +121,8 @@
 - :py:meth:`invert_no_zero`
 """
 
+from typing import Tuple
+
 import datetime
 import numpy as np
 import scipy.linalg as la
@@ -1229,6 +1231,79 @@ def get_crate_channel(slot, sma):
     return default
 
 
+def get_default_frequency_map_stream() -> Tuple[np.ndarray, np.ndarray]:
+    """Get the default CHIME frequency map stream.
+
+    Level order is [shuffle, crate, slot, link].
+
+    Returns
+    -------
+    stream : np.ndarray (np.int32)
+        [shuffle, crate, slot, link] for each frequency bin
+    stream_id : np.ndarray (np.int64)
+        stream_id for each map combination
+        shuffle*2**12 + crate*2**8 + slot*2**4 + link
+    """
+    stream = np.empty((1024, 4), dtype=np.int32)
+
+    # shuffle
+    stream[:, 0] = 3
+    # crate
+    stream[:, 1] = np.tile(np.arange(2).repeat(16), 32)
+    # slot
+    stream[:, 2] = np.tile(np.arange(16), 64)
+    # link
+    stream[:, 3] = np.tile(np.arange(8).repeat(32), 4)
+
+    stream_id = (
+        stream[:, 0] * 2**12
+        + stream[:, 1] * 2**12
+        + stream[:, 2] * 2**4
+        + stream[:, 3]
+    )
+
+    return stream, stream_id.astype(np.int64)
+
+
+def order_frequency_map_stream(fmap: np.ndarray, stream_id: np.ndarray) -> np.ndarray:
+    """Order stream_id components based on a frequency map.
+
+    Level order is [shuffle, crate, slot, link]
+
+    Parameters
+    ----------
+    fmap : np.ndarray[int]
+        frequency map
+    stream_id : np.ndarray[int]
+        1-D array of stream_ids associated with each row in fmap
+
+    Returns
+    -------
+    stream : np.ndarray[nfreq, 4]
+        shuffle, crate, slot, link for each frequency
+    """
+
+    def decode_stream_id(sid) -> tuple[int]:
+        link = sid & 15
+        slot = (sid >> 4) & 15
+        crate = (sid >> 8) & 15
+        shuffle = (sid >> 12) & 15
+
+        return (shuffle, crate, slot, link)
+
+    decoded_stream = [decode_stream_id(i) for i in stream_id[:]]
+    x = [[] for _ in range(len(stream_id))]
+
+    for ii, freqs in enumerate(fmap):
+        for f in freqs:
+            x[f].append(decoded_stream[ii])
+
+    # TODO: maybe implement some checks here
+    stream = np.array([i[0] for i in x], dtype=np.int32)
+
+    return stream
+
+
 def get_correlator_inputs(lay_time, correlator=None, connect=True):
     """Get the information for all channels in a layout.