update that how to judge the same weight

[mengle-yang]

update that weights and how to judge the index depend on offset

What is the purpose of the change

1.update that how to judge the same weight
2.update that weights and how to judge the index depend on offset

Brief changelog

1.enhance performance
2.code is clear

Verifying this change

XXXXX

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[wenbochang888]

it is very clear. The totalWeight != weight * (i + 1) is very clever. very nice