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Add Integer::log variants #80918

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Jul 7, 2021
Merged

Add Integer::log variants #80918

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188 changes: 188 additions & 0 deletions library/core/src/num/int_macros.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1744,6 +1744,194 @@ macro_rules! int_impl {
}
}

/// Returns the logarithm of the number with respect to an arbitrary base.
///
/// This method may not be optimized owing to implementation details;
/// `log2` can produce results more efficiently for base 2, and `log10`
/// can produce results more efficiently for base 10.
///
/// # Panics
///
/// When the number is zero, or if the base is not at least 2; it
/// panics in debug mode and the return value is wrapped to 0 in release
/// mode (the only situation in which the method can return 0).
///
/// # Examples
///
/// ```
/// #![feature(int_log)]
#[doc = concat!("assert_eq!(5", stringify!($SelfT), ".log(5), 1);")]
/// ```
#[unstable(feature = "int_log", issue = "70887")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
#[track_caller]
#[rustc_inherit_overflow_checks]
#[allow(arithmetic_overflow)]
pub const fn log(self, base: Self) -> Self {
match self.checked_log(base) {
Some(n) => n,
None => {
// In debug builds, trigger a panic on None.
// This should optimize completely out in release builds.
let _ = Self::MAX + 1;

0
},
}
}

/// Returns the base 2 logarithm of the number.
///
/// # Panics
///
/// When the number is zero it panics in debug mode and the return value
/// is wrapped to 0 in release mode (the only situation in which the
/// method can return 0).
///
/// # Examples
///
/// ```
/// #![feature(int_log)]
#[doc = concat!("assert_eq!(2", stringify!($SelfT), ".log2(), 1);")]
/// ```
#[unstable(feature = "int_log", issue = "70887")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
#[track_caller]
#[rustc_inherit_overflow_checks]
#[allow(arithmetic_overflow)]
pub const fn log2(self) -> Self {
match self.checked_log2() {
Some(n) => n,
None => {
// In debug builds, trigger a panic on None.
// This should optimize completely out in release builds.
let _ = Self::MAX + 1;

0
},
}
}

/// Returns the base 10 logarithm of the number.
///
/// # Panics
///
/// When the number is zero it panics in debug mode and the return value
/// is wrapped to 0 in release mode (the only situation in which the
/// method can return 0).
///
/// # Example
///
/// ```
/// #![feature(int_log)]
#[doc = concat!("assert_eq!(10", stringify!($SelfT), ".log10(), 1);")]
/// ```
#[unstable(feature = "int_log", issue = "70887")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
#[track_caller]
#[rustc_inherit_overflow_checks]
#[allow(arithmetic_overflow)]
pub const fn log10(self) -> Self {
match self.checked_log10() {
Some(n) => n,
None => {
// In debug builds, trigger a panic on None.
// This should optimize completely out in release builds.
let _ = Self::MAX + 1;

0
},
}
}

/// Returns the logarithm of the number with respect to an arbitrary base.
///
/// Returns `None` if the number is negative or zero, or if the base is not at least 2.
///
/// This method may not be optimized owing to implementation details;
/// `checked_log2` can produce results more efficiently for base 2, and
/// `checked_log10` can produce results more efficiently for base 10.
///
/// # Examples
///
/// ```
/// #![feature(int_log)]
#[doc = concat!("assert_eq!(5", stringify!($SelfT), ".checked_log(5), Some(1));")]
/// ```
#[unstable(feature = "int_log", issue = "70887")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub const fn checked_log(self, base: Self) -> Option<Self> {
if self <= 0 || base <= 1 {
None
} else {
let mut n = 0;
let mut r = self;

// Optimization for 128 bit wide integers.
if Self::BITS == 128 {
let b = Self::log2(self) / (Self::log2(base) + 1);
n += b;
r /= base.pow(b as u32);
}

while r >= base {
r /= base;
n += 1;
}
Some(n)
}
}

/// Returns the base 2 logarithm of the number.
///
/// Returns `None` if the number is negative or zero.
///
/// # Examples
///
/// ```
/// #![feature(int_log)]
#[doc = concat!("assert_eq!(2", stringify!($SelfT), ".checked_log2(), Some(1));")]
/// ```
#[unstable(feature = "int_log", issue = "70887")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub const fn checked_log2(self) -> Option<Self> {
if self <= 0 {
None
} else {
// SAFETY: We just checked that this number is positive
let log = (Self::BITS - 1) as Self - unsafe { intrinsics::ctlz_nonzero(self) };
Some(log)
}
}

/// Returns the base 10 logarithm of the number.
///
/// Returns `None` if the number is negative or zero.
///
/// # Example
///
/// ```
/// #![feature(int_log)]
#[doc = concat!("assert_eq!(10", stringify!($SelfT), ".checked_log10(), Some(1));")]
/// ```
#[unstable(feature = "int_log", issue = "70887")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub const fn checked_log10(self) -> Option<Self> {
self.checked_log(10)
}

/// Computes the absolute value of `self`.
///
/// # Overflow behavior
Expand Down
188 changes: 188 additions & 0 deletions library/core/src/num/uint_macros.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -634,6 +634,194 @@ macro_rules! uint_impl {
}
}

/// Returns the logarithm of the number with respect to an arbitrary base.
///
/// This method may not be optimized owing to implementation details;
/// `log2` can produce results more efficiently for base 2, and `log10`
/// can produce results more efficiently for base 10.
///
/// # Panics
///
/// When the number is negative, zero, or if the base is not at least 2;
/// it panics in debug mode and the return value is wrapped to 0 in
/// release mode (the only situation in which the method can return 0).
///
/// # Examples
///
/// ```
/// #![feature(int_log)]
#[doc = concat!("assert_eq!(5", stringify!($SelfT), ".log(5), 1);")]
/// ```
#[unstable(feature = "int_log", issue = "70887")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
#[track_caller]
#[rustc_inherit_overflow_checks]
#[allow(arithmetic_overflow)]
pub const fn log(self, base: Self) -> Self {
match self.checked_log(base) {
Some(n) => n,
None => {
// In debug builds, trigger a panic on None.
// This should optimize completely out in release builds.
let _ = Self::MAX + 1;

0
},
}
}

/// Returns the base 2 logarithm of the number.
///
/// # Panics
///
/// When the number is negative or zero it panics in debug mode and
/// the return value is wrapped to 0 in release mode (the only situation in
/// which the method can return 0).
///
/// # Examples
///
/// ```
/// #![feature(int_log)]
#[doc = concat!("assert_eq!(2", stringify!($SelfT), ".log2(), 1);")]
/// ```
#[unstable(feature = "int_log", issue = "70887")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
#[track_caller]
#[rustc_inherit_overflow_checks]
#[allow(arithmetic_overflow)]
pub const fn log2(self) -> Self {
match self.checked_log2() {
Some(n) => n,
None => {
// In debug builds, trigger a panic on None.
// This should optimize completely out in release builds.
let _ = Self::MAX + 1;

0
},
}
}

/// Returns the base 10 logarithm of the number.
///
/// # Panics
///
/// When the number is negative or zero it panics in debug mode and the
/// return value is wrapped to 0 in release mode (the only situation in
/// which the method can return 0).
///
/// # Example
///
/// ```
/// #![feature(int_log)]
#[doc = concat!("assert_eq!(10", stringify!($SelfT), ".log10(), 1);")]
/// ```
#[unstable(feature = "int_log", issue = "70887")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
#[track_caller]
#[rustc_inherit_overflow_checks]
#[allow(arithmetic_overflow)]
pub const fn log10(self) -> Self {
match self.checked_log10() {
Some(n) => n,
None => {
// In debug builds, trigger a panic on None.
// This should optimize completely out in release builds.
let _ = Self::MAX + 1;

0
},
}
}

/// Returns the logarithm of the number with respect to an arbitrary base.
///
/// Returns `None` if the number is zero, or if the base is not at least 2.
///
/// This method may not be optimized owing to implementation details;
/// `checked_log2` can produce results more efficiently for base 2, and
/// `checked_log10` can produce results more efficiently for base 10.
///
/// # Examples
///
/// ```
/// #![feature(int_log)]
#[doc = concat!("assert_eq!(5", stringify!($SelfT), ".checked_log(5), Some(1));")]
/// ```
#[unstable(feature = "int_log", issue = "70887")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub const fn checked_log(self, base: Self) -> Option<Self> {
if self <= 0 || base <= 1 {
None
} else {
let mut n = 0;
let mut r = self;

// Optimization for 128 bit wide integers.
if Self::BITS == 128 {
let b = Self::log2(self) / (Self::log2(base) + 1);
n += b;
r /= base.pow(b as u32);
}

while r >= base {
r /= base;
n += 1;
}
Some(n)
}
}

/// Returns the base 2 logarithm of the number.
///
/// Returns `None` if the number is zero.
///
/// # Examples
///
/// ```
/// #![feature(int_log)]
#[doc = concat!("assert_eq!(2", stringify!($SelfT), ".checked_log2(), Some(1));")]
/// ```
#[unstable(feature = "int_log", issue = "70887")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub const fn checked_log2(self) -> Option<Self> {
if self <= 0 {
None
} else {
// SAFETY: We just checked that this number is positive
let log = (Self::BITS - 1) as Self - unsafe { intrinsics::ctlz_nonzero(self) };
Some(log)
}
}

/// Returns the base 10 logarithm of the number.
///
/// Returns `None` if the number is zero.
///
/// # Examples
///
/// ```
/// #![feature(int_log)]
#[doc = concat!("assert_eq!(10", stringify!($SelfT), ".checked_log10(), Some(1));")]
/// ```
#[unstable(feature = "int_log", issue = "70887")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub const fn checked_log10(self) -> Option<Self> {
self.checked_log(10)
}

/// Checked negation. Computes `-self`, returning `None` unless `self ==
/// 0`.
///
Expand Down
1 change: 1 addition & 0 deletions library/core/tests/lib.rs
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -45,6 +45,7 @@
#![feature(try_trait_v2)]
#![feature(slice_internals)]
#![feature(slice_partition_dedup)]
#![feature(int_log)]
#![feature(iter_advance_by)]
#![feature(iter_partition_in_place)]
#![feature(iter_intersperse)]
Expand Down
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