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# SPDX-License-Identifier: Apache-2.0
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
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#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
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import torch
import torch.nn as nn


def swish(x):
    return x * torch.sigmoid(x)


class SinusoidalPositionalEncoding(nn.Module):
    """
    Produces a sinusoidal encoding of shape (B, T, w)
    given timesteps of shape (B, T).
    """

    def __init__(self, embedding_dim):
        super().__init__()
        self.embedding_dim = embedding_dim

    def forward(self, timesteps):
        # timesteps: shape (B, T)
        # We'll compute sin/cos frequencies across dim T
        timesteps = timesteps.float()  # ensure float

        b, t = timesteps.shape
        device = timesteps.device

        half_dim = self.embedding_dim // 2
        # typical log space frequencies for sinusoidal encoding
        exponent = -torch.arange(half_dim, dtype=torch.float, device=device) * (
            torch.log(torch.tensor(10000.0)) / half_dim
        )
        # Expand timesteps to (B, T, 1) then multiply
        freqs = timesteps.unsqueeze(-1) * exponent.exp()  # (B, T, half_dim)

        sin = torch.sin(freqs)
        cos = torch.cos(freqs)
        enc = torch.cat([sin, cos], dim=-1)  # (B, T, w)

        return enc