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from functools import partial
import torch
import torch.nn.functional as F
from einops import rearrange
from rotary_embedding_torch import RotaryEmbedding, broadcat
from torch import nn
# helpers
def exists(val):
return val is not None
def default(val, d):
return val if exists(val) else d
def cast_tuple(val, depth = 1):
if isinstance(val, list):
val = tuple(val)
return val if isinstance(val, tuple) else (val,) * depth
def max_neg_value(t):
return -torch.finfo(t.dtype).max
def stable_softmax(t, dim = -1, alpha = 32 ** 2):
t = t / alpha
t = t - torch.amax(t, dim = dim, keepdim = True).detach()
return (t * alpha).softmax(dim = dim)
def route_args(router, args, depth):
routed_args = [(dict(), dict()) for _ in range(depth)]
matched_keys = [key for key in args.keys() if key in router]
for key in matched_keys:
val = args[key]
for depth, ((f_args, g_args), routes) in enumerate(zip(routed_args, router[key])):
new_f_args, new_g_args = map(lambda route: ({key: val} if route else {}), routes)
routed_args[depth] = ({**f_args, **new_f_args}, {**g_args, **new_g_args})
return routed_args
# classes
class SequentialSequence(nn.Module):
def __init__(self, layers, args_route = {}, layer_dropout = 0.):
super().__init__()
assert all(len(route) == len(layers) for route in args_route.values()), 'each argument route map must have the same depth as the number of sequential layers'
self.layers = layers
self.args_route = args_route
self.layer_dropout = layer_dropout
def forward(self, x, **kwargs):
args = route_args(self.args_route, kwargs, len(self.layers))
layers_and_args = list(zip(self.layers, args))
for (f, g), (f_args, g_args) in layers_and_args:
x = x + f(x, **f_args)
x = x + g(x, **g_args)
return x
class DivideMax(nn.Module):
def __init__(self, dim):
super().__init__()
self.dim = dim
def forward(self, x):
maxes = x.amax(dim = self.dim, keepdim = True).detach()
return x / maxes
# https://arxiv.org/abs/2103.17239
class LayerScale(nn.Module):
def __init__(self, dim, depth, fn):
super().__init__()
if depth <= 18:
init_eps = 0.1
elif depth > 18 and depth <= 24:
init_eps = 1e-5
else:
init_eps = 1e-6
scale = torch.zeros(1, 1, dim).fill_(init_eps)
self.scale = nn.Parameter(scale)
self.fn = fn
def forward(self, x, **kwargs):
return self.fn(x, **kwargs) * self.scale
# layer norm
class PreNorm(nn.Module):
def __init__(self, dim, fn, sandwich = False):
super().__init__()
self.norm = nn.LayerNorm(dim)
self.norm_out = nn.LayerNorm(dim) if sandwich else nn.Identity()
self.fn = fn
def forward(self, x, **kwargs):
x = self.norm(x)
x = self.fn(x, **kwargs)
return self.norm_out(x)
# feed forward
class GEGLU(nn.Module):
def forward(self, x):
x, gates = x.chunk(2, dim = -1)
return x * F.gelu(gates)
class FeedForward(nn.Module):
def __init__(self, dim, dropout = 0., mult = 4.):
super().__init__()
self.net = nn.Sequential(
nn.Linear(dim, dim * mult * 2),
GEGLU(),
nn.Dropout(dropout),
nn.Linear(dim * mult, dim)
)
def forward(self, x):
return self.net(x)
# Attention
class Attention(nn.Module):
def __init__(self, dim, seq_len, causal = True, heads = 8, dim_head = 64, dropout = 0.):
super().__init__()
inner_dim = dim_head * heads
self.heads = heads
self.seq_len = seq_len
self.scale = dim_head ** -0.5
self.causal = causal
self.to_qkv = nn.Linear(dim, inner_dim * 3, bias = False)
self.to_out = nn.Sequential(
nn.Linear(inner_dim, dim),
nn.Dropout(dropout)
)
def forward(self, x, mask = None):
b, n, _, h, device = *x.shape, self.heads, x.device
softmax = torch.softmax
qkv = self.to_qkv(x).chunk(3, dim = -1)
q, k, v = map(lambda t: rearrange(t, 'b n (h d) -> b h n d', h = h), qkv)
q = q * self.scale
dots = torch.einsum('b h i d, b h j d -> b h i j', q, k)
mask_value = max_neg_value(dots)
if exists(mask):
mask = rearrange(mask, 'b j -> b () () j')
dots.masked_fill_(~mask, mask_value)
del mask
if self.causal:
i, j = dots.shape[-2:]
mask = torch.ones(i, j, device = device).triu_(j - i + 1).bool()
dots.masked_fill_(mask, mask_value)
attn = softmax(dots, dim=-1)
out = torch.einsum('b h i j, b h j d -> b h i d', attn, v)
out = rearrange(out, 'b h n d -> b n (h d)')
out = self.to_out(out)
return out
# main transformer class
class Transformer(nn.Module):
def __init__(
self,
*,
dim,
depth,
seq_len,
causal = True,
heads = 8,
dim_head = 64,
ff_mult = 4,
attn_dropout = 0.,
ff_dropout = 0.,
sparse_attn = False,
sandwich_norm = False,
):
super().__init__()
layers = nn.ModuleList([])
sparse_layer = cast_tuple(sparse_attn, depth)
for ind, sparse_attn in zip(range(depth), sparse_layer):
attn = Attention(dim, causal = causal, seq_len = seq_len, heads = heads, dim_head = dim_head, dropout = attn_dropout)
ff = FeedForward(dim, mult = ff_mult, dropout = ff_dropout)
layers.append(nn.ModuleList([
LayerScale(dim, ind + 1, PreNorm(dim, attn, sandwich = sandwich_norm)),
LayerScale(dim, ind + 1, PreNorm(dim, ff, sandwich = sandwich_norm))
]))
execute_type = SequentialSequence
route_attn = ((True, False),) * depth
attn_route_map = {'mask': route_attn}
self.layers = execute_type(layers, args_route = attn_route_map)
def forward(self, x, **kwargs):
return self.layers(x, **kwargs)
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