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Document that last_pos_per_query is inclusive in flash attention. - #1058
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The masks in SingleFlashAttentionRowVector and DoubleFlashAttentionRowVector keep keys in [pos, last_pos] (mask_size = last_pos + 1 - pos), and all callers pass the index of the last attended key (e.g. tiled_attention.cc uses the query's own position, vit.cc uses num_tokens - 1). The ComputeQKMacroTile doc block said "(exclusive)" and the public header comment was unclear. Comment-only change, no behavior change. PiperOrigin-RevId: 999337547
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Document that last_pos_per_query is inclusive in flash attention.
The masks in SingleFlashAttentionRowVector and
DoubleFlashAttentionRowVector keep keys in [pos, last_pos]
(mask_size = last_pos + 1 - pos), and all callers pass the index of the
last attended key (e.g. tiled_attention.cc uses the query's own position,
vit.cc uses num_tokens - 1). The ComputeQKMacroTile doc block said
"(exclusive)" and the public header comment was unclear. Comment-only
change, no behavior change.