rope_embeddings.py

# --------------------------------------------------------
# Adapted from EVA CLIP
# https://github.com/baaivision/EVA/tree/master/EVA-CLIP/rei/eva_clip
# --------------------------------------------------------

from math import pi

import torch
from einops import rearrange, repeat
from torch import nn


def broadcast(tensors, dim=-1):
    num_tensors = len(tensors)
    shape_lens = set(list(map(lambda t: len(t.shape), tensors)))
    assert len(shape_lens) == 1, 'tensors must all have the same number of dimensions'
    shape_len = list(shape_lens)[0]
    dim = (dim + shape_len) if dim < 0 else dim
    dims = list(zip(*map(lambda t: list(t.shape), tensors)))
    expandable_dims = [(i, val) for i, val in enumerate(dims) if i != dim]
    assert all(
        [*map(lambda t: len(set(t[1])) <= 2, expandable_dims)]
    ), 'invalid dimensions for broadcastable concatentation'
    max_dims = list(map(lambda t: (t[0], max(t[1])), expandable_dims))
    expanded_dims = list(map(lambda t: (t[0], (t[1],) * num_tensors), max_dims))
    expanded_dims.insert(dim, (dim, dims[dim]))
    expandable_shapes = list(zip(*map(lambda t: t[1], expanded_dims)))
    tensors = list(map(lambda t: t[0].expand(*t[1]), zip(tensors, expandable_shapes)))
    return torch.cat(tensors, dim=dim)


def rotate_half(x):
    x = rearrange(x, '... (d r) -> ... d r', r=2)
    x1, x2 = x.unbind(dim=-1)
    x = torch.stack((-x2, x1), dim=-1)
    return rearrange(x, '... d r -> ... (d r)')


class VisionRotaryEmbedding(nn.Module):
    def __init__(
        self,
        dim,
        pt_seq_len,
        ft_seq_len=None,
        custom_freqs=None,
        freqs_for='lang',
        theta=10000,
        max_freq=10,
        num_freqs=1,
    ):
        super().__init__()
        if custom_freqs:
            freqs = custom_freqs
        elif freqs_for == 'lang':
            freqs = 1.0 / (
                theta ** (torch.arange(0, dim, 2)[: (dim // 2)].float() / dim)
            )
        elif freqs_for == 'pixel':
            freqs = torch.linspace(1.0, max_freq / 2, dim // 2) * pi
        elif freqs_for == 'constant':
            freqs = torch.ones(num_freqs).float()
        else:
            raise ValueError(f'unknown modality {freqs_for}')

        if ft_seq_len is None:
            ft_seq_len = pt_seq_len
        t = torch.arange(ft_seq_len) / ft_seq_len * pt_seq_len

        freqs_h = torch.einsum('..., f -> ... f', t, freqs)
        freqs_h = repeat(freqs_h, '... n -> ... (n r)', r=2)

        freqs_w = torch.einsum('..., f -> ... f', t, freqs)
        freqs_w = repeat(freqs_w, '... n -> ... (n r)', r=2)

        freqs = broadcast((freqs_h[:, None, :], freqs_w[None, :, :]), dim=-1)

        self.register_buffer('freqs_cos', freqs.cos(), persistent=False)
        self.register_buffer('freqs_sin', freqs.sin(), persistent=False)

    def forward(self, t, start_index=0):
        rot_dim = self.freqs_cos.shape[-1]
        end_index = start_index + rot_dim
        assert rot_dim <= t.shape[-1], (
            f'feature dimension {t.shape[-1]} is not of sufficient size to rotate in '
            f'all the positions {rot_dim}'
        )
        t_left, t, t_right = (
            t[..., :start_index],
            t[..., start_index:end_index],
            t[..., end_index:],
        )
        t = (t * self.freqs_cos) + (rotate_half(t) * self.freqs_sin)

        return torch.cat((t_left, t, t_right), dim=-1)


class VisionRotaryEmbeddingFast(nn.Module):
    def __init__(
        self,
        dim,
        pt_seq_len,
        ft_seq_len=None,
        custom_freqs=None,
        freqs_for='lang',
        theta=10000,
        max_freq=10,
        num_freqs=1,
        patch_dropout=0.0,
    ):
        super().__init__()
        if custom_freqs:
            freqs = custom_freqs
        elif freqs_for == 'lang':
            freqs = 1.0 / (
                theta ** (torch.arange(0, dim, 2)[: (dim // 2)].float() / dim)
            )
        elif freqs_for == 'pixel':
            freqs = torch.linspace(1.0, max_freq / 2, dim // 2) * pi
        elif freqs_for == 'constant':
            freqs = torch.ones(num_freqs).float()
        else:
            raise ValueError(f'unknown modality {freqs_for}')

        if ft_seq_len is None:
            ft_seq_len = pt_seq_len
        t = torch.arange(ft_seq_len) / ft_seq_len * pt_seq_len

        freqs = torch.einsum('..., f -> ... f', t, freqs)
        freqs = repeat(freqs, '... n -> ... (n r)', r=2)
        freqs = broadcast((freqs[:, None, :], freqs[None, :, :]), dim=-1)

        freqs_cos = freqs.cos().view(-1, freqs.shape[-1])
        freqs_sin = freqs.sin().view(-1, freqs.shape[-1])

        self.patch_dropout = patch_dropout

        self.register_buffer('freqs_cos', freqs_cos, persistent=False)
        self.register_buffer('freqs_sin', freqs_sin, persistent=False)

    def forward(self, t, patch_indices_keep=None):
        if patch_indices_keep is not None:
            batch = t.size()[0]
            batch_indices = torch.arange(batch)
            batch_indices = batch_indices[..., None]

            freqs_cos = repeat(
                self.freqs_cos, 'i j -> n i m j', n=t.shape[0], m=t.shape[1]
            )
            freqs_sin = repeat(
                self.freqs_sin, 'i j -> n i m j', n=t.shape[0], m=t.shape[1]
            )

            freqs_cos = freqs_cos[batch_indices, patch_indices_keep]
            freqs_cos = rearrange(freqs_cos, 'n i m j -> n m i j')
            freqs_sin = freqs_sin[batch_indices, patch_indices_keep]
            freqs_sin = rearrange(freqs_sin, 'n i m j -> n m i j')

            return t * freqs_cos + rotate_half(t) * freqs_sin

        return t * self.freqs_cos + rotate_half(t) * self.freqs_sin