alamb commented on code in PR #9453:
URL: https://github.com/apache/arrow-rs/pull/9453#discussion_r3343230008
##########
arrow-buffer/src/bigint/mod.rs:
##########
@@ -614,6 +614,101 @@ impl i256 {
let n = (n.high >> 64) as i64; // throw away the lower 192 bits
(n as f64) * f64::powi(2.0, 192 - (k as i32)) // convert to f64 and
scale it, as we left-shift k bit previous, so we need to scale it by 2^(192-k)
}
+
+ /// Computes the `base` logarithm of the number `self`
+ /// Returns `None` if `self` is less than or equal to zero, or if `base`
is less than 2.
+ #[inline]
+ pub fn checked_ilog(self, base: i256) -> Option<u32> {
+ if base == Self::from(10) {
+ // Faster implementation for base 10
+ return self.checked_ilog10();
+ }
+
+ if self <= Self::ZERO {
+ return None;
+ }
+ if base <= Self::ONE {
+ return None;
+ }
+ if self <= base {
Review Comment:
Update: yes I think it should -- here is a PR that fixes it on your forl:
- https://github.com/theirix/arrow-rs/pull/1
##########
arrow-buffer/src/bigint/mod.rs:
##########
@@ -614,6 +614,101 @@ impl i256 {
let n = (n.high >> 64) as i64; // throw away the lower 192 bits
(n as f64) * f64::powi(2.0, 192 - (k as i32)) // convert to f64 and
scale it, as we left-shift k bit previous, so we need to scale it by 2^(192-k)
}
+
+ /// Computes the `base` logarithm of the number `self`
+ /// Returns `None` if `self` is less than or equal to zero, or if `base`
is less than 2.
+ #[inline]
+ pub fn checked_ilog(self, base: i256) -> Option<u32> {
+ if base == Self::from(10) {
+ // Faster implementation for base 10
+ return self.checked_ilog10();
+ }
+
+ if self <= Self::ZERO {
+ return None;
+ }
+ if base <= Self::ONE {
+ return None;
+ }
+ if self <= base {
Review Comment:
Shouldn't ilog(n, n) be 1 (not zero)?
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