modeling_gamma.py

import torch
from torch import nn 
from typing import Optional , Tuple , List
from torch.nn import CrossEntropyLoss
import math
from model_siglip import SiglipVisionConfig , SiglipVisionModel
class KVCache():

    def __init__(self) -> None:
        self.key_cache: List[torch.Tensor] = []
        self.value_cache: List[torch.Tensor] = []
    
    def num_items(self) -> int:
        if len(self.key_cache) == 0:
            return 0
        else:
            # The shape of the key_cache is [Batch_Size, Num_Heads_KV, Seq_Len, Head_Dim]
            return self.key_cache[0].shape[-2]

    def update(
        self,
        key_states: torch.Tensor,
        value_states: torch.Tensor,
        layer_idx: int,
    ) -> Tuple[torch.Tensor, torch.Tensor]:
        if len(self.key_cache) <= layer_idx:
            # If we never added anything to the KV-Cache of this layer, let's create it.
            self.key_cache.append(key_states)
            self.value_cache.append(value_states)
        else:
            # ... otherwise we concatenate the new keys with the existing ones.
            # each tensor has shape: [Batch_Size, Num_Heads_KV, Seq_Len, Head_Dim]
            self.key_cache[layer_idx] = torch.cat([self.key_cache[layer_idx], key_states], dim=-2)
            self.value_cache[layer_idx] = torch.cat([self.value_cache[layer_idx], value_states], dim=-2)

        # ... and then we return all the existing keys + the new ones.
        return self.key_cache[layer_idx], self.value_cache[layer_idx]

class GemmaConfig():

    def __init__(
        self,
        vocab_size,
        hidden_size,
        intermediate_size,
        num_hidden_layers,
        num_attention_heads,
        num_key_value_heads,
        head_dim=256,
        max_position_embeddings=8192,
        rms_norm_eps=1e-6,
        rope_theta=10000.0,
        attention_bias=False,
        attention_dropout=0.0,
        pad_token_id=None,
        **kwargs,
    ):
        super().__init__()
        self.vocab_size = vocab_size
        self.max_position_embeddings = max_position_embeddings
        self.hidden_size = hidden_size
        self.intermediate_size = intermediate_size
        self.num_hidden_layers = num_hidden_layers
        self.num_attention_heads = num_attention_heads
        self.head_dim = head_dim
        self.num_key_value_heads = num_key_value_heads
        self.rms_norm_eps = rms_norm_eps
        self.rope_theta = rope_theta
        self.attention_bias = attention_bias
        self.attention_dropout = attention_dropout
        self.pad_token_id = pad_token_id

class PaliGemmaConfig():

    def __init__(
        self,
        vision_config=None,
        text_config=None,
        ignore_index=-100,
        image_token_index=256000,
        vocab_size=257152,
        projection_dim=2048,
        hidden_size=2048,
        pad_token_id=None,
        **kwargs,
    ):
        super().__init__()
        self.ignore_index = ignore_index
        self.image_token_index = image_token_index
        self.vocab_size = vocab_size
        self.projection_dim = projection_dim
        self.hidden_size = hidden_size
        self.vision_config = vision_config
        self.is_encoder_decoder = False
        self.pad_token_id = pad_token_id

        self.vision_config = SiglipVisionConfig(**vision_config)
        self.text_config = text_config

        self.text_config = GemmaConfig(**text_config, pad_token_id=pad_token_id)
        self.vocab_size = self.text_config.vocab_size

        self.text_config.num_image_tokens = (self.vision_config.image_size // self.vision_config.patch_size) ** 2
        self.vision_config.projection_dim = projection_dim


class GemmaRMSNorm(nn.Module):
    def __init__(self, dim:int , eps :float = 1e-6):
        super.__init__()
        self.eps = eps 
        self.weight = nn.Parameter(torch.zeros(dim))

    def _norm(self , x):
        return x * torch.rsqrt(x.pow(2).mean(-1 , keepdim = True) + self.esp)
    
    def forward(self, x ):
        output = self._norm(x.float())
        output = output * (1.0 + self.weight.float())
        return output.type_as(x)
    
class GemmaMLP(nn.Module):
    def __init__(self, config):
        super().__init__()
        self.config = config
        self.hidden_size = config.hidden_size
        self.intermediate_size = config.intermediate_size
        self.gate_proj = nn.Linear(self.hidden_size, self.intermediate_size, bias=False)
        self.up_proj = nn.Linear(self.hidden_size, self.intermediate_size, bias=False)
        self.down_proj = nn.Linear(self.intermediate_size, self.hidden_size, bias=False)

    def forward(self , x ):
        # Equivalent to:
        # y = self.gate_proj(x) # [Batch_Size, Seq_Len, Hidden_Size] -> [Batch_Size, Seq_Len, Intermediate_Size]
        # y = torch.gelu(y, approximate="tanh") # [Batch_Size, Seq_Len, Intermediate_Size]
        # j = self.up_proj(x) # [Batch_Size, Seq_Len, Hidden_Size] -> [Batch_Size, Seq_Len, Intermediate_Size]
        # z = y * j # [Batch_Size, Seq_Len, Intermediate_Size]
        # z = self.down_proj(z) # [Batch_Size, Seq_Len, Intermediate_Size] -> [Batch_Size, Seq_Len, Hidden_Size]
        return self.down_proj(nn.functional.gelu(self.gate_proj(x), approximate="tanh") * self.up_proj(x))

def repeat_kv(hidden_states: torch.Tensor, n_rep: int) -> torch.Tensor:
    batch, num_key_value_heads, slen, head_dim = hidden_states.shape
    if n_rep == 1:
        return hidden_states
    hidden_states = hidden_states[:, :, None, :, :].expand(batch, num_key_value_heads, n_rep, slen, head_dim)
    return hidden_states.reshape(batch, num_key_value_heads * n_rep, slen, head_dim)


class GemmaRotaryEmbedding(nn.Module):
    def __init__(self, dim , max_position_embeddings = 2048 , base = 10000 , device = None):
        super().__init__()
        self.dim = dim 
        self.max_position_embeddings = max_position_embeddings
        self.base = base 

        inv_freq = 1.0 / (self.base ** (torch.arange(0, self.dim , 2 , dtype=torch.int64).float()/self.dim))
        self.register_buffer("inv_freq", tensor=inv_freq, persistent=False)

    @torch.no_grad()
    def forward(self, x, position_ids, seq_len=None):
        # x: [bs, num_attention_heads, seq_len, head_size]
        self.inv_freq.to(x.device)
        # Copy the inv_freq tensor for batch in the sequence
        # inv_freq_expanded: [Batch_Size, Head_Dim // 2, 1]
        inv_freq_expanded = self.inv_freq[None, :, None].float().expand(position_ids.shape[0], -1, 1)
        # position_ids_expanded: [Batch_Size, 1, Seq_Len]
        position_ids_expanded = position_ids[:, None, :].float()
        device_type = x.device.type
        device_type = device_type if isinstance(device_type, str) and device_type != "mps" else "cpu"
        with torch.autocast(device_type=device_type, enabled=False):
            # Multiply each theta by the position (which is the argument of the sin and cos functions)
            # freqs: [Batch_Size, Head_Dim // 2, 1] @ [Batch_Size, 1, Seq_Len] --> [Batch_Size, Seq_Len, Head_Dim // 2]
            freqs = (inv_freq_expanded.float() @ position_ids_expanded.float()).transpose(1, 2)
            # emb: [Batch_Size, Seq_Len, Head_Dim]
            emb = torch.cat((freqs, freqs), dim=-1)
            # cos, sin: [Batch_Size, Seq_Len, Head_Dim]
            cos = emb.cos()
            sin = emb.sin()
        return cos.to(dtype=x.dtype), sin.to(dtype=x.dtype)


def rotate_half(x):
    # Build the [-x2, x1, -x4, x3, ...] tensor for the sin part of the positional encoding.
    x1 = x[..., : x.shape[-1] // 2] # Takes the first half of the last dimension
    x2 = x[..., x.shape[-1] // 2 :] # Takes the second half of the last dimension
    return torch.cat((-x2, x1), dim=-1)


def apply_rotary_pos_emb(q, k, cos, sin, unsqueeze_dim=1):
    cos = cos.unsqueeze(unsqueeze_dim) # Add the head dimension
    sin = sin.unsqueeze(unsqueeze_dim) # Add the head dimension
    # Apply the formula (34) of the Rotary Positional Encoding paper.
    q_embed = (q * cos) + (rotate_half(q) * sin)
    k_embed = (k * cos) + (rotate_half(k) * sin)
    return q_embed, k_embed


class GammaAttention(nn.Module):
    def __init__(self, config:GemmaConfig , layer_idx : Optional[int] = None ):
        super().__init__()
        self.config = config
        self.layer_idx = layer_idx

        self.attention_dropout = config.attention_dropout
        self.hidden_size = config.hidden_size
        self.num_heads = config.num_attention_heads
        self.head_dim = config.head_dim
        self.num_key_value_heads = config.num_key_value_heads
        self.num_key_value_groups = self.num_heads // self.num_key_value_heads
        self.max_position_embeddings = config.max_position_embeddings
        self.rope_theta = config.rope_theta
        self.is_causal = True

        assert self.hidden_size % self.num_heads == 0            

        self.q_proj = nn.Linear(self.hidden_size, self.num_heads * self.head_dim, bias=config.attention_bias)
        self.k_proj = nn.Linear(self.hidden_size, self.num_key_value_heads * self.head_dim, bias=config.attention_bias)
        self.v_proj = nn.Linear(self.hidden_size, self.num_key_value_heads * self.head_dim, bias=config.attention_bias)
        self.o_proj = nn.Linear(self.num_heads * self.head_dim, self.hidden_size, bias=config.attention_bias)
        self.rotary_emb = GemmaRotaryEmbedding(
            self.head_dim,
            max_position_embeddings=self.max_position_embeddings,
            base=self.rope_theta,
        )
    def forward(
        self,
        hidden_states: torch.Tensor,
        attention_mask: Optional[torch.Tensor] = None,
        position_ids: Optional[torch.LongTensor] = None,
        kv_cache: Optional[KVCache] = None,
        **kwargs,
    ) -> Tuple[torch.Tensor, Optional[torch.Tensor], Optional[Tuple[torch.Tensor]]]:
        
        bsz , q_len , _ = hidden_states.size()
        query_states = self.q_proj(hidden_states)
        key_states = self.k_proj(hidden_states)
        value_states = self.v_proj(hidden_states)

        query_states = query_states.view(bsz , q_len , self.num_heads , self.head_dim).transpose(1,2)

        key_states = key_states.view(bsz, q_len, self.num_key_value_heads, self.head_dim).transpose(1, 2)

        value_states = value_states.view(bsz, q_len, self.num_key_value_heads, self.head_dim).transpose(1, 2)

        cos , sin = self.rotary_emb(value_states , position_ids , seq_len=None )
        query_states , key_states = apply_rotary_pos_emb(query_states , key_states , cos , sin )

        if kv_cache is not None:
            key_states , value_states = kv_cache.update(key_states, value_states, self.layer_idx )

        key_states = repeat_kv(key_states, self.num_key_value_groups)
        value_states = repeat_kv(value_states, self.num_key_value_groups)
        # Perform the calculation as usual, Q * K^T / sqrt(head_dim). Shape: [Batch_Size, Num_Heads_Q, Seq_Len_Q, Seq_Len_KV]
        attn_weights = torch.matmul(query_states, key_states.transpose(2, 3)) / math.sqrt(self.head_dim) 

        assert attention_mask is not None
        attn_weights = attn_weights + attention_mask

        attn_weights = nn.functional.softmax(attn_weights ,dim=-1 , dtype=torch.float32).to(query_states.dtype)
        attn_weights = nn.functional.dropout(attn_weights, p=self.attention_dropout, training=self.training)
        attn_output = torch.matmul(attn_weights, value_states)

        if attn_output.size() != (bsz, self.num_heads, q_len, self.head_dim):
            raise ValueError(
                f"`attn_output` should be of size {(bsz, self.num_heads, q_len, self.head_dim)}, but is"
                f" {attn_output.size()}"
            )
        
        attn_output = attn_output.transpose(1,2).contiguous()

        attn_output = attn_output.view(bsz , q_len , -1)

        attn_output = self.o_proj(attn_output)

        return attn_output , attn_weights
        

class GemmaDeocderLayer(nn.Module):
    def __init__(self, config: GemmaConfig , layer_idx : int):
        super().__init__()
        self.hidden_size = config.hidden_size
        self.mlp = GemmaMLP(config)
        self.input_layernorm = GemmaRMSNorm(config.hidden_size , eps= config.rms_norm_eps)
        self.post_attention_layernorm = GemmaRMSNorm(config.hidden_size , eps = config.rms_norm_eps)

    def forward(
        self,
        hidden_states: torch.Tensor,
        attention_mask: Optional[torch.Tensor] = None,
        position_ids: Optional[torch.LongTensor] = None,
        kv_cache: Optional[KVCache] = None,
    ) -> Tuple[torch.FloatTensor, Optional[Tuple[torch.FloatTensor, torch.FloatTensor]]]:
        residual = hidden_states
        # [Batch_Size, Seq_Len, Hidden_Size]
        hidden_states = self.input_layernorm(hidden_states)

        # [Batch_Size, Seq_Len, Hidden_Size]
        hidden_states, _, = self.self_attn(
            hidden_states=hidden_states,
            attention_mask=attention_mask,
            position_ids=position_ids,
            kv_cache=kv_cache,
        )
        # [Batch_Size, Seq_Len, Hidden_Size]
        hidden_states = residual + hidden_states

        # [Batch_Size, Seq_Len, Hidden_Size]
        residual = hidden_states
        # [Batch_Size, Seq_Len, Hidden_Size]
        hidden_states = self.post_attention_layernorm(hidden_states)
        # [Batch_Size, Seq_Len, Hidden_Size]
        hidden_states = self.mlp(hidden_states)
        # [Batch_Size, Seq_Len, Hidden_Size]
        hidden_states = residual + hidden_states

        return hidden_states


class GemmaModel(nn.Module):

    def __init__(self, config: GemmaConfig):
        super().__init__()
        self.config = config
        self.padding_idx = config.pad_token_id
        self.vocab_size = config.vocab_size

        self.embed_tokens = nn.Embedding(config.vocab_size, config.hidden_size, self.padding_idx)
        self.layers = nn.ModuleList(
            [GemmaDecoderLayer(config, layer_idx) for layer_idx in range(config.num_hidden_layers)]
        )
        self.norm = GemmaRMSNorm(config.hidden_size, eps=config.rms_norm_eps)

    def get_input_embeddings(self):
        return self.embed_tokens

    # Ignore copy
    def forward(
        self,
        attention_mask: Optional[torch.Tensor] = None,
        position_ids: Optional[torch.LongTensor] = None,
        inputs_embeds: Optional[torch.FloatTensor] = None,
        kv_cache: Optional[KVCache] = None,
    ) -> torch.FloatTensor:
        # [Batch_Size, Seq_Len, Hidden_Size]
        hidden_states = inputs_embeds
        # [Batch_Size, Seq_Len, Hidden_Size]
        normalizer = torch.tensor(self.config.hidden_size**0.5, dtype=hidden_states.dtype)
        hidden_states = hidden_states * normalizer

        for decoder_layer in self.layers:
            # [Batch_Size, Seq_Len, Hidden_Size]
            hidden_states = decoder_layer(
                hidden_states,
                attention_mask=attention_mask,
                position_ids=position_ids,
                kv_cache=kv_cache,
            )

        # [Batch_Size, Seq_Len, Hidden_Size]
        hidden_states = self.norm(hidden_states)

        # [Batch_Size, Seq_Len, Hidden_Size]
        return hidden_states


class GemmaForCausalLM(nn.Module):
    def __init__(self, config):
        super().__init__()
        self.config= config
        self.model = GemmaModel(config)
        self.vocab_size = config.vocab_size
        self.lm_head = nn.Linear(config.hidden_size , config.vocab_size , bias=False)

    def get_input_embeddings(self):
        return self.model.embed_tokens
    
    def tie_weights(self):
        self.lm_head.weight = self.model.embed_tokens.weight
    
    def forward(
        self,
        attention_mask: Optional[torch.Tensor] = None,
        position_ids: Optional[torch.LongTensor] = None,
        inputs_embeds: Optional[torch.FloatTensor] = None,
        kv_cache: Optional[KVCache] = None,
    ) -> Tuple:
        
        outputs = self.model(
            attention_mask=attention_mask,
            position_ids=position_ids,
            inputs_embeds=inputs_embeds,
            kv_cache=kv_cache,
        )

        hidden_states = outputs
        logits = self.lm_head(hidden_states)
        logits = logits.float()

        return_data = {
            "logits": logits,
        }

        if kv_cache is not None:
            return_data["kv_cache"] = kv_cache

        return return_data

class PaliGemmaMultiProjector(nn.Module):
    def __init__(self, config : PaliGemmaConfig):
        super().__init__()
        self.linear = nn.Linear(config.vision_config.hidden_size, config.vision_config.projection_dim , bias = True)

    def forward(self , image_features):
        hidden_states = self.linear(image_features)
        return hidden_states


class PaligammaforconditionalGeneration(nn.Module):
    def __init__(self, config: PaliGemmaConfig):
        super().__init__()
        self.config = config
        self.vision_tower = SiglipVisionModel(config.vision_config)
        self.multi_modal_projector = PaliGemmaMultiModalProjector(config)
        self.vocab_size = config.vocab_size

        language_model = GemmaForCausalLM(config.text_config)
        self.language_model = language_model

        self.pad_token_id = self.config.pad_token_id if self.config.pad_token_id is not None else -1

    def tie_weights(self):
        return self.language_model.tie_weights()
    
    def _merge_input_ids_with_image_features(
            self, image_features :torch.Tensor , inputs_embeds : torch.Tensor , input_ids: torch.Tensor , attention_mask : torch.Tensor , kv_cache: Optional[KVcache]= None
    ):
        _ , _ , embed_dim = image_features.shape 
        batch_size , sequence_length = input_ids.shape
        dtype , device = inputs_embeds.dtype , inputs_embeds.device
        scaled_image_features = image_features / (self.config.hidden_size**0.5)

        final_embeddings = torch.zeros(batch_size, sequence_length, embed_dim , dtype= inputs_embeds.dtype , device=inputs_embeds.device)
        text_mask = (input_ids != self.config.image_token_index) & (input_ids != self.pad_token_id)
        # Shape: [Batch_Size, Seq_Len]. True for image tokens
        image_mask = input_ids == self.config.image_token_index
        # Shape: [Batch_Size, Seq_Len]. True for padding tokens
        pad_mask = input_ids == self.pad_token_id

        # We need to expand the masks to the embedding dimension otherwise we can't use them in torch.where
        text_mask_expanded = text_mask.unsqueeze(-1).expand(-1, -1, embed_dim)
        pad_mask_expanded = pad_mask.unsqueeze(-1).expand(-1, -1, embed_dim)
        image_mask_expanded = image_mask.unsqueeze(-1).expand(-1, -1, embed_dim)

        # Add the text embeddings
        final_embedding = torch.where(text_mask_expanded, inputs_embeds, final_embedding)
        # Insert image embeddings. We can't use torch.where because the sequence length of scaled_image_features is not equal to the sequence length of the final embedding
        final_embedding = final_embedding.masked_scatter(image_mask_expanded, scaled_image_features)
        # Zero out padding tokens
        final_embedding = torch.where(pad_mask_expanded, torch.zeros_like(final_embedding), final_embedding)
        
        dtype, device = inputs_embeds.dtype, inputs_embeds.device
        min_dtype = torch.finfo(dtype).min
        q_len = inputs_embeds.shape[1]
    
        if kv_cache is None or kv_cache.num_items() == 0:
            # Do not mask any token, because we're in the prefill phase
            # This only works when we have no padding
            causal_mask = torch.full(
                (batch_size, q_len, q_len), fill_value=0, dtype=dtype, device=device
            )
        else:
            # Since we are generating tokens, the query must be one single token
            assert q_len == 1
            kv_len = kv_cache.num_items() + q_len
            # Also in this case we don't need to mask anything, since each query should be able to attend all previous tokens. 
            # This only works when we have no padding
            causal_mask = torch.full(
                (batch_size, q_len, kv_len), fill_value=0, dtype=dtype, device=device
            )
        causal_mask = causal_mask.unsqueeze(1)

        if kv_cache is not None and kv_cache.num_items() > 0:
            # The position of the query is just the last position
            position_ids = attention_mask.cumsum(-1)[:, -1]
            if position_ids.dim() == 1:
                position_ids = position_ids.unsqueeze(0)
        else:
            # Create a position_ids based on the size of the attention_mask
            # For masked tokens, use the number 1 as position.
            position_ids = (attention_mask.cumsum(-1)).masked_fill_((attention_mask == 0), 1).to(device)

        return final_embedding, causal_mask, position_ids


    def forward(self, 
                input_ids:torch.LongTensor = None  , 
                pixel_values:torch.FloatTensor = None, 
                attention_mask : Optional[torch.Tensor] = None, 
                kv_cache :Optional[KVcache] = None, 
                  )-> Tuple:
        assert torch.all(attention_mask == -1), "the input should not be added : ) "

        input_embed = self.language_model.get_input_embeddings()(input_ids)

        selected_image_feature = self.vision_tower(pixel_values.to(input_embed.dtype))
        
        image_features = self.multi_modal_projector(selected_image_feature)

        input_embed , attention_mask , position_ids = self._merge_input_ids_with_image_features(image_features , input_embed , input_ids ,attention_mask , kv_cache )

        outputs = self.language_model(
            attention_mask = attention_mask, 
            position_ids=position_ids,
            input_embed = input_embed,
            kv_cache= kv_cache, 
        )
        return outputs