[Util] introduce calculate_matvec_accumulator_range

src/finn/util/basic.py

@@ -259,6 +259,33 @@ def pad_tensor_to_multiple_of(ndarray, pad_to_dims, val=0, distr_pad=False):
     return ret
 
 
+def calculate_matvec_accumulator_range(matrix, vec_dt):
+    """Calculate the minimum and maximum possible result (accumulator) values
+    for a dot product x * A, given matrix A of dims (MW, MH), and vector (1, MW)
+    with datatype vec_dt. Returns (acc_min, acc_max).
+    """
+    min_weight = matrix.min()
+    max_weight = matrix.max()
+    perceptive_field_elems = matrix.shape[0]
+    min_input = vec_dt.min()
+    max_input = vec_dt.max()
+    # calculate minimum and maximum values of accumulator
+    # assume inputs span the whole range of the input datatype
+    acc_min = perceptive_field_elems * min(
+        min_weight * max_input,
+        min_weight * min_input,
+        max_weight * max_input,
+        max_weight * min_input,
+    )
+    acc_max = perceptive_field_elems * max(
+        min_weight * max_input,
+        min_weight * min_input,
+        max_weight * max_input,
+        max_weight * min_input,
+    )
+    return (acc_min, acc_max)
+
+
 def gen_finn_dt_tensor(finn_dt, tensor_shape):
     """Generates random tensor in given shape and with given FINN DataType."""
     if type(tensor_shape) == list: