[kgm] refactor #2: slightly improve performance
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@ -29,17 +29,27 @@ impl DecipherV3 {
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impl Decipher for DecipherV3 {
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fn decrypt(&self, buffer: &mut [u8], offset: usize) {
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let slot_key_stream = self.slot_key.iter().cycle().skip(offset);
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let file_key_stream = self.file_key.iter().cycle().skip(offset);
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let slot_key_stream = self
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.slot_key
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.iter()
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.cycle()
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.skip(offset % self.slot_key.len());
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let file_key_stream = self
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.file_key
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.iter()
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.cycle()
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.skip(offset % self.file_key.len());
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let mut offset = offset as u32;
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let key_stream = slot_key_stream.zip(file_key_stream);
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for (datum, (&slot_key, &file_key)) in buffer.iter_mut().zip(key_stream) {
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let offset_key = offset.to_ne_bytes().iter().fold(0, |acc, &x| acc ^ x);
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let mut temp = *datum;
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temp ^= file_key;
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temp ^= temp.wrapping_shl(4);
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temp ^= slot_key;
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temp ^= offset.to_ne_bytes().iter().fold(0, |acc, &x| acc ^ x);
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temp ^= offset_key;
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*datum = temp;
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offset = offset.wrapping_add(1);
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