viirya commented on code in PR #4303:
URL: https://github.com/apache/arrow-rs/pull/4303#discussion_r1211126905
##########
arrow-buffer/src/bigint.rs:
##########
@@ -396,42 +407,93 @@ impl i256 {
.then_some(Self { low, high })
}
+ /// Return the least number of bits needed to represent the number
+ #[inline]
+ fn bits_required(&self) -> usize {
+ let arr = self.to_le_bytes();
+ let iter = arr.iter().rev().take(32 - 1);
+ if self.is_negative() {
+ let ctr = iter.take_while(|&&b| b == ::core::u8::MAX).count();
+ (8 * (32 - ctr)) + 1 - (!arr[32 - ctr - 1]).leading_zeros() as
usize
+ } else {
+ let ctr = iter.take_while(|&&b| b == ::core::u8::MIN).count();
+ (8 * (32 - ctr)) + 1 - arr[32 - ctr - 1].leading_zeros() as usize
+ }
+ }
+
+ /// divmod like operation, returns (quotient, remainder)
+ #[inline]
+ fn div_rem(self, other: Self) -> Result<(Self, Self), I256Error> {
+ if other == Self::ZERO {
+ return Err(I256Error::DivideByZero);
+ }
+ if other.is_negative() && self == Self::MIN && other ==
Self::ONE.wrapping_neg() {
+ return Err(I256Error::DivideOverflow);
+ }
+
+ if self == Self::MIN || other == Self::MIN {
+ let l = BigInt::from_signed_bytes_le(&self.to_le_bytes());
+ let r = BigInt::from_signed_bytes_le(&other.to_le_bytes());
+ let d = i256::from_bigint_with_overflow(&l / &r).0;
+ let r = i256::from_bigint_with_overflow(&l % &r).0;
+ return Ok((d, r));
+ }
+
+ let mut me = self.checked_abs().unwrap();
+ let mut you = other.checked_abs().unwrap();
+ let mut ret = [0u8; 32];
+ if me < you {
+ return Ok((Self::from_le_bytes(ret), self));
+ }
+
Review Comment:
The low component is u128. If the high component is zero, it might be
possibly over i128 range, no?
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