Add padding='same' for dilation=1, stride=1

Author: papkov

fft_conv_pytorch/fft_conv.py

@@ -5,6 +5,7 @@
 import torch.nn.functional as f
 from torch import Tensor, nn
 from torch.fft import irfftn, rfftn
+from math import ceil, floor
 
 
 def complex_matmul(a: Tensor, b: Tensor, groups: int = 1) -> Tensor:
@@ -55,7 +56,7 @@ def fft_conv(
     signal: Tensor,
     kernel: Tensor,
     bias: Tensor = None,
-    padding: Union[int, Iterable[int]] = 0,
+    padding: Union[int, Iterable[int], str] = 0,
     padding_mode: str = "constant",
     stride: Union[int, Iterable[int]] = 1,
     dilation: Union[int, Iterable[int]] = 1,
@@ -69,19 +70,31 @@ def fft_conv(
         signal: (Tensor) Input tensor to be convolved with the kernel.
         kernel: (Tensor) Convolution kernel.
         bias: (Tensor) Bias tensor to add to the output.
-        padding: (Union[int, Iterable[int]) Number of zero samples to pad the
-            input on the last dimension.
+        padding: (Union[int, Iterable[int], str) If int, Number of zero samples to pad then
+            input on the last dimension. If str, "same" supported to pad input for size preservation.
+        padding_mode: (str) Padding mode to use from {constant, reflection, replication}.
+                      reflection not available for 3d.
         stride: (Union[int, Iterable[int]) Stride size for computing output values.
+        dilation: (Union[int, Iterable[int]) Dilation rate for the kernel.
+        groups: (int) Number of groups for the convolution.
 
     Returns:
         (Tensor) Convolved tensor
     """
 
     # Cast padding, stride & dilation to tuples.
     n = signal.ndim - 2
-    padding_ = to_ntuple(padding, n=n)
     stride_ = to_ntuple(stride, n=n)
     dilation_ = to_ntuple(dilation, n=n)
+    if isinstance(padding, str):
+        if padding == "same":
+            if stride != 1 or dilation != 1:
+                raise ValueError("stride must be 1 for padding='same'.")
+            padding_ = [(k - 1) / 2 for k in kernel.shape[2:]]
+        else:
+            raise ValueError(f"Padding mode {padding} not supported.")
+    else:
+        padding_ = to_ntuple(padding, n=n)
 
     # internal dilation offsets
     offset = torch.zeros(1, 1, *dilation_, device=signal.device, dtype=signal.dtype)
@@ -93,8 +106,8 @@ def fft_conv(
     # pad the kernel internally according to the dilation parameters
     kernel = torch.kron(kernel, offset)[(slice(None), slice(None)) + cutoff]
 
-    # Pad the input signal & kernel tensors
-    signal_padding = [p for p in padding_[::-1] for _ in range(2)]
+    # Pad the input signal & kernel tensors (round to support even sized convolutions)
+    signal_padding = [r(p) for p in padding_[::-1] for r in (floor, ceil)]
     signal = f.pad(signal, signal_padding, mode=padding_mode)
 
     # Because PyTorch computes a *one-sided* FFT, we need the final dimension to
@@ -155,9 +168,14 @@ def __init__(
             out_channels: (int) Number of channels in output tensors
             kernel_size: (Union[int, Iterable[int]) Square radius of the kernel
             padding: (Union[int, Iterable[int]) Number of zero samples to pad the
-                input on the last dimension.
+                input on the last dimension. If str, "same" supported to pad input for size preservation.
+            padding_mode: (str) Padding mode to use from {constant, reflection, replication}.
+                          reflection not available for 3d.
             stride: (Union[int, Iterable[int]) Stride size for computing output values.
+            dilation: (Union[int, Iterable[int]) Dilation rate for the kernel.
+            groups: (int) Number of groups for the convolution.
             bias: (bool) If True, includes bias, which is added after convolution
+            ndim: (int) Number of dimensions of the input tensor.
         """
         super().__init__()
         self.in_channels = in_channels

tests/test_functional.py

@@ -12,7 +12,7 @@
 @pytest.mark.parametrize("out_channels", [2, 3])
 @pytest.mark.parametrize("groups", [1, 2, 3])
 @pytest.mark.parametrize("kernel_size", [2, 3])
-@pytest.mark.parametrize("padding", [0, 1])
+@pytest.mark.parametrize("padding", [0, 1, "same"])
 @pytest.mark.parametrize("stride", [1, 2])
 @pytest.mark.parametrize("dilation", [1, 2])
 @pytest.mark.parametrize("bias", [True])
@@ -30,6 +30,10 @@ def test_fft_conv_functional(
     ndim: int,
     input_size: int,
 ):
+    if padding == "same" and (stride != 1 or dilation != 1):
+        # padding='same' is not compatible with strided convolutions
+        return
+
     torch_conv = getattr(f, f"conv{ndim}d")
     groups = _gcd(in_channels, _gcd(out_channels, groups))
 
@@ -70,7 +74,7 @@ def test_fft_conv_functional(
 @pytest.mark.parametrize("out_channels", [2, 3])
 @pytest.mark.parametrize("groups", [1, 2, 3])
 @pytest.mark.parametrize("kernel_size", [2, 3])
-@pytest.mark.parametrize("padding", [0, 1])
+@pytest.mark.parametrize("padding", [0, 1, "same"])
 @pytest.mark.parametrize("stride", [1, 2])
 @pytest.mark.parametrize("dilation", [1, 2])
 @pytest.mark.parametrize("bias", [True])
@@ -88,6 +92,10 @@ def test_fft_conv_backward_functional(
     ndim: int,
     input_size: int,
 ):
+    if padding == "same" and (stride != 1 or dilation != 1):
+        # padding='same' is not compatible with strided convolutions
+        return
+
     torch_conv = getattr(f, f"conv{ndim}d")
     groups = _gcd(in_channels, _gcd(out_channels, groups))
 

tests/test_module.py

@@ -30,6 +30,10 @@ def test_fft_conv_module(
     ndim: int,
     input_size: int,
 ):
+    if padding == "same" and (stride != 1 or dilation != 1):
+        # padding='same' is not compatible with strided convolutions
+        return
+
     torch_conv = getattr(f, f"conv{ndim}d")
     groups = _gcd(in_channels, _gcd(out_channels, groups))
     fft_conv_layer = _FFTConv(
@@ -85,6 +89,10 @@ def test_fft_conv_backward_module(
     ndim: int,
     input_size: int,
 ):
+    if padding == "same" and (stride != 1 or dilation != 1):
+        # padding='same' is not compatible with strided convolutions
+        return
+
     torch_conv = getattr(f, f"conv{ndim}d")
     groups = _gcd(in_channels, _gcd(out_channels, groups))
     fft_conv_layer = _FFTConv(