diff --git a/models/common.py b/models/common.py
new file mode 100644
index 0000000..6821023
--- /dev/null
+++ b/models/common.py
@@ -0,0 +1,141 @@
+from typing import Tuple
+
+import torch
+import torch.nn as nn
+from torch import Graph, Tensor, Value
+
+
+def make_anchors(feats: Tensor,
+                 strides: Tensor,
+                 grid_cell_offset: float = 0.5) -> Tuple[Tensor, Tensor]:
+    anchor_points, stride_tensor = [], []
+    assert feats is not None
+    dtype, device = feats[0].dtype, feats[0].device
+    for i, stride in enumerate(strides):
+        _, _, h, w = feats[i].shape
+        sx = torch.arange(end=w, device=device,
+                          dtype=dtype) + grid_cell_offset  # shift x
+        sy = torch.arange(end=h, device=device,
+                          dtype=dtype) + grid_cell_offset  # shift y
+        sy, sx = torch.meshgrid(sy, sx)
+        anchor_points.append(torch.stack((sx, sy), -1).view(-1, 2))
+        stride_tensor.append(
+            torch.full((h * w, 1), stride, dtype=dtype, device=device))
+    return torch.cat(anchor_points), torch.cat(stride_tensor)
+
+
+class TRT_NMS(torch.autograd.Function):
+
+    @staticmethod
+    def forward(
+            ctx: Graph,
+            boxes: Tensor,
+            scores: Tensor,
+            iou_threshold: float = 0.65,
+            score_threshold: float = 0.25,
+            max_output_boxes: int = 100,
+            background_class: int = -1,
+            box_coding: int = 0,
+            plugin_version: str = '1',
+            score_activation: int = 0
+    ) -> Tuple[Tensor, Tensor, Tensor, Tensor]:
+        batch_size, num_boxes, num_classes = scores.shape
+        num_det = torch.randint(0,
+                                max_output_boxes, (batch_size, 1),
+                                dtype=torch.int32)
+        det_boxes = torch.randn(batch_size, max_output_boxes, 4)
+        det_scores = torch.randn(batch_size, max_output_boxes)
+        det_classes = torch.randint(0,
+                                    num_classes,
+                                    (batch_size, max_output_boxes),
+                                    dtype=torch.int32)
+
+        return num_det, det_boxes, det_scores, det_classes
+
+    @staticmethod
+    def symbolic(
+            g,
+            boxes: Value,
+            scores: Value,
+            iou_threshold: float = 0.45,
+            score_threshold: float = 0.25,
+            max_output_boxes: int = 100,
+            background_class: int = -1,
+            box_coding: int = 0,
+            score_activation: int = 0,
+            plugin_version: str = '1') -> Tuple[Value, Value, Value, Value]:
+        out = g.op('TRT::EfficientNMS_TRT',
+                   boxes,
+                   scores,
+                   iou_threshold_f=iou_threshold,
+                   score_threshold_f=score_threshold,
+                   max_output_boxes_i=max_output_boxes,
+                   background_class_i=background_class,
+                   box_coding_i=box_coding,
+                   plugin_version_s=plugin_version,
+                   score_activation_i=score_activation,
+                   outputs=4)
+        nums_dets, boxes, scores, classes = out
+        return nums_dets, boxes, scores, classes
+
+
+class C2f(nn.Module):
+
+    def __init__(self,
+                 c1,
+                 c2,
+                 n=1,
+                 shortcut=False,
+                 g=1,
+                 e=0.5):  # ch_in, ch_out, number, shortcut, groups, expansion
+        super().__init__()
+
+    def forward(self, x):
+        y = list(self.cv1(x).split((self.c, self.c), 1))
+        x = self.cv1(x)
+        y = [x, x[:, self.c:, ...]]
+        y.extend(m(y[-1]) for m in self.m)
+        y.pop(1)
+        return self.cv2(torch.cat(y, 1))
+
+
+class PostDetect(nn.Module):
+    export = True
+    shape = None
+    dynamic = False
+    iou_thres = 0.65
+    conf_thres = 0.25
+    topk = 100
+
+    def __init__(self, nc=80, ch=()):
+        super().__init__()
+
+    def forward(self, x):
+        shape = x[0].shape
+        b, res = shape[0], []
+        for i in range(self.nl):
+            res.append(torch.cat((self.cv2[i](x[i]), self.cv3[i](x[i])), 1))
+        if self.dynamic or self.shape != shape:
+            self.anchors, self.strides = (x.transpose(
+                0, 1) for x in make_anchors(x, self.stride, 0.5))
+            self.shape = shape
+        x = [i.view(b, self.no, -1) for i in res]
+        y = torch.cat(x, 2)
+        box, cls = y[:, :self.reg_max * 4, ...], y[:, self.reg_max * 4:,
+                                                   ...].sigmoid()
+        box = box.view(b, 4, self.reg_max, -1).permute(0, 1, 3, 2).contiguous()
+        box = box.softmax(-1) @ torch.arange(self.reg_max).to(box)
+        box0, box1 = -box[:, :2, ...], box[:, 2:, ...]
+        box = self.anchors.repeat(b, 2, 1) + torch.cat([box0, box1], 1)
+        box = box * self.strides
+
+        return TRT_NMS.apply(box.transpose(1, 2), cls.transpose(1, 2),
+                             self.iou_thres, self.conf_thres, self.topk)
+
+
+def optim(module: nn.Module):
+    s = str(type(module))[6:-2].split('.')[-1]
+    if s == 'Detect':
+        setattr(module, '__class__', PostDetect)
+    elif s == 'C2f':
+        setattr(module, '__class__', C2f)