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# SPDX-License-Identifier: Apache-2.0
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# http://www.apache.org/licenses/LICENSE-2.0
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"""
Imaginaire4 Attention Subpackage:
Unified implementation for all Attention implementations.

Mask utilities
"""

from enum import Enum


class CausalType(Enum):
    """
    Different types of causal masking supported by backends of interest.
    """

    # Top-Left: Simplified: mask if q_idx < kv_idx
    # CUTLASS / NATTEN default
    # Q = 2, KV = 5:
    # O____
    # OO___
    #
    # Q = 5, KV = 2:
    # O_
    # OO
    # OO
    # OO
    # OO
    TopLeft = 0

    # Bottom-right: mask if q_idx + KV - Q < kv_idx
    # Flash Attention default
    # Q = 2, KV = 5:
    # OOOO_
    # OOOOO
    #
    # Q = 5, KV = 2:
    # __
    # __
    # __
    # O_
    # OO
    BottomRight = 1

    # When seqlen_q == seqlen_kv, we don't care about the causal type
    # because top-left and bottom-right are equivalent
    DontCare = 2