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Optimize twos_complement and from_signed_bytes_be #231

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Optimize twos_complement and from_signed_bytes_be #231

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af77c78
Optimize twos_complement
Bond-009 Dec 14, 2021
d8746da
Remove extra alloc in from_signed_bytes_be
Bond-009 Dec 14, 2021
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19 changes: 9 additions & 10 deletions src/bigint/convert.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -377,9 +377,10 @@ pub(super) fn from_signed_bytes_be(digits: &[u8]) -> BigInt {

if sign == Sign::Minus {
// two's-complement the content to retrieve the magnitude
let mut digits = Vec::from(digits);
twos_complement_be(&mut digits);
BigInt::from_biguint(sign, BigUint::from_bytes_be(&*digits))
let mut digits = digits.to_vec();
digits.reverse();
twos_complement_le(&mut digits);
BigInt::from_biguint(sign, BigUint::from_bytes_le(&digits))
} else {
BigInt::from_biguint(sign, BigUint::from_bytes_be(digits))
}
Expand All @@ -395,9 +396,9 @@ pub(super) fn from_signed_bytes_le(digits: &[u8]) -> BigInt {

if sign == Sign::Minus {
// two's-complement the content to retrieve the magnitude
let mut digits = Vec::from(digits);
let mut digits = digits.to_vec();
twos_complement_le(&mut digits);
BigInt::from_biguint(sign, BigUint::from_bytes_le(&*digits))
BigInt::from_biguint(sign, BigUint::from_bytes_le(&digits))
} else {
BigInt::from_biguint(sign, BigUint::from_bytes_le(digits))
}
Expand Down Expand Up @@ -460,10 +461,8 @@ where
{
let mut carry = true;
for d in digits {
*d = !*d;
if carry {
*d = d.wrapping_add(1);
carry = d.is_zero();
}
let (val, tmp_carry) = (!*d).overflowing_add(carry as u8);
*d = val;
carry = tmp_carry;
}
}