added builder for prefix mask

Project_Model/Libs/Transformer/Utils/attention_mask.py

@@ -15,12 +15,16 @@ def get_causal_attention_mask_with_prefix(seq_len, prefix):
     mask[:,:prefix] = False
     return mask
 
-def get_prefix_causal_mask_from_padding_mask(seq_len, prefix_mask):
+def get_prefix_causal_mask_from_padding_mask(seq_len:int, prefix_mask, att_heads:int=1):
+    expanded_padding_mask = prefix_mask.unsqueeze(-1).repeat(1, 1, seq_len)         # B,T,T
+    expanded_padding_mask = expanded_padding_mask.permute(0,2,1)                    # B,T,T
+    mask = torch.triu(torch.ones(seq_len, seq_len, dtype=torch.bool), diagonal=1)   #   T,T
+    tri_batched = mask.unsqueeze(0)                                                 # 1,T,T will broadcast over B
+    prefix_causal_mask = expanded_padding_mask & tri_batched
+    prefix_causal_mask = prefix_causal_mask.repeat_interleave(att_heads, dim=0)     # B*H,T,T
+    return prefix_causal_mask
+
 
 
-"""
 print(get_causal_attention_mask_with_prefix(10,3))
-seq_len = 10
-prefix = 3
-mask = torch.arange(seq_len) >= prefix
-"""
+