因為固定長度，所以checksum呢件事保證會有重覆（白鴿籠原則）

但對於某一特定chekcum
譬如 ba1f2511fc30423bdbb183fe33f3dd0f
有冇保證會有重覆呢？
（好似唔關programming事）

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xader

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發表於 2024-3-27 19:01 | 只看該作者

但對於某一特定chekcum
譬如 ba1f2511fc30423bdbb183fe33f3dd0f
有冇保證會有重覆呢？
（好似唔關program ...
Wiwacomia 發表於 2024-3-27 15:09

你講緊咩? 你都識講 pigeonhole principle, 每個 checksum 都可以 derived from many inputs

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Wiwacomia

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發表於 2024-3-27 19:20 | 只看該作者

你講緊咩? 你都識講 pigeonhole principle, 每個 checksum 都可以 derived from many inputs ...
xader 發表於 2024-3-27 19:01

32位＝只有固定個獨立數值，多咗input＝有啲output會重覆，
唔代表必然有多個input可以生成特定ba1f....呢個output呀。
可以無限個input生成有限個32位數字，其中每個output出現頻率不同呀

以上係單憑白鴿籠原則諗出來，
實際條數點生成冇睇

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xader

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Rank: 2 Rank: 2

4^#

發表於 2024-3-27 20:52 | 只看該作者

32位＝只有固定個獨立數值，多咗input＝有啲output會重覆，
唔代表必然有多個input可以生成特定ba1f.... ...
Wiwacomia 發表於 2024-3-27 19:20

Uniformity
A good hash function should map the expected inputs as evenly as possible over its output range. That is, every hash value in the output range should be generated with roughly the same probability. The reason for this last requirement is that the cost of hashing-based methods goes up sharply as the number of collisions—pairs of inputs that are mapped to the same hash value—increases. If some hash values are more likely to occur than others, a larger fraction of the lookup operations will have to search through a larger set of colliding table entries.

你講緊 Hash function uniformity

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Wiwacomia