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chore(integer): simplify radix decryption

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tmontaigu
2023-03-09 10:30:01 +01:00
parent 06713fa42d
commit bb6663cfe5
1 changed files with 24 additions and 18 deletions
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42
tfhe/src/integer/client_key/mod.rs
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@@ -288,40 +288,46 @@ impl ClientKey {
) where
F: Fn(&crate::shortint::ClientKey, &crate::shortint::Ciphertext) -> u64,
{
// limit to know when we have at least 64 bits
// of decrypted data
const U64_MODULUS: u128 = 1 << 64;
#[cfg(target_endian = "little")]
let clear_words_iter = clear_words.iter_mut();
#[cfg(target_endian = "big")]
let clear_words_iter = clear_words.iter_mut().rev();
let mut cipher_blocks_iter = ctxt.blocks.iter();
let mut current = 0u128;
let mut power = 1u128;
let mut power_excess = 1;
let mut bit_buffer = 0u128;
let mut valid_until_power = 1u128;
for current_clear_word in clear_words_iter {
for cipher_block in cipher_blocks_iter.by_ref() {
let block_value = decrypt_block(&self.key, cipher_block) as u128;
let shifted_block_value = block_value * power * power_excess;
current += shifted_block_value;
let shifted_block_value = block_value * valid_until_power;
bit_buffer += shifted_block_value;
let new_power = power * self.key.parameters.message_modulus.0 as u128;
let pow_dif = (new_power * power_excess) / (1u128 << 64);
valid_until_power *= self.key.parameters.message_modulus.0 as u128;
if pow_dif >= 1 {
power_excess = pow_dif;
power = 1;
if valid_until_power >= U64_MODULUS {
// We have enough data to fill the current word
// e.g.
// bit_buffer: [b0, ..., b64, b65, b66, b67,..., b128]
// ^ ^
// | |-> valid_until_power
// | = end of decrypted bits (not
// inclusive) |-> U64_MODULUS
break;
} else {
power = new_power;
}
}
if power == 1 {
*current_clear_word = (current & u128::from(u64::MAX)) as u64;
current = current.wrapping_shr(64);
} else {
*current_clear_word = (current & ((power * power_excess) - 1)) as u64;
}
// We want to take at most 64 bits of data from the bit buffer
// since our words are 64 bits
let power_to_write = std::cmp::min(valid_until_power, U64_MODULUS);
let mask = power_to_write - 1;
*current_clear_word = (bit_buffer & mask) as u64;
bit_buffer /= power_to_write;
valid_until_power /= power_to_write;
}
}