add docstring

Author: calad0i

hls4ml/backends/vivado/passes/reshaping_templates.py

@@ -128,6 +128,25 @@ def format(self, node):
 
 
 def permute_config_gen(name: str, shape: tuple[int, ...], perm: tuple[int, ...]):
+    """
+    Generate a configuration string for a permute operation. Operates by mapping the output index to input input index by:
+     - unravel the output index
+     - map each dimension to the corresponding stride in the input tensor, sum
+    The operation can be expressed as:
+
+    new_shape = tuple(shape[i] for i in perm)
+    strides = np.cumprod((shapes[1:] + (1,))[::-1])[::-1]
+    perm_strides = [strides[i] for i in perm]
+    out[index] = inp[np.dot(np.unravel_index(index, new_shape), perm_strides)]
+
+    Args:
+        name (str): The name of the configuration.
+        shape (tuple[int, ...]): The shape of the input tensor.
+        perm (tuple[int, ...]): The permutation of the dimensions.
+
+    Returns:
+        str: The formatted configuration string for the permute operation.
+    """
     new_shape = tuple(shape[i] for i in perm)
     strides = np.cumprod((shape[1:] + (1,))[::-1])[::-1]
     perm_strides = tuple(int(strides[i]) for i in perm)