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Rollup merge of #92956 - scottmcm:nonzero-log2, r=dtolnay

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Add `log2` and `log10` to `NonZeroU*`

This version is nice in that it doesn't need to worry about zeros, and thus doesn't have any error cases.

cc `int_log` tracking issue #70887

(I didn't add them to `NonZeroI*` despite it being on `i*` since allowing negatives bring back the error cases again.)
This commit is contained in:
Matthias Krüger 2022-01-17 20:07:09 +01:00 • committed by GitHub
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5 changed files with 206 additions and 150 deletions
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265
library/core/src/num/int_log10.rs
View file

@ -1,141 +1,140 @@
mod unchecked {
// 0 < val <= u8::MAX
#[inline]
pub const fn u8(val: u8) -> u32 {
let val = val as u32;
/// These functions compute the integer logarithm of their type, assuming
/// that someone has already checked that the the value is strictly positive.
// For better performance, avoid branches by assembling the solution
// in the bits above the low 8 bits.
// 0 < val <= u8::MAX
#[inline]
pub const fn u8(val: u8) -> u32 {
let val = val as u32;
// Adding c1 to val gives 10 in the top bits for val < 10, 11 for val >= 10
const C1: u32 = 0b11_00000000 - 10; // 758
// Adding c2 to val gives 01 in the top bits for val < 100, 10 for val >= 100
const C2: u32 = 0b10_00000000 - 100; // 412
// For better performance, avoid branches by assembling the solution
// in the bits above the low 8 bits.
// Value of top bits:
// +c1 +c2 1&2
// 0..=9 10 01 00 = 0
// 10..=99 11 01 01 = 1
// 100..=255 11 10 10 = 2
((val + C1) & (val + C2)) >> 8
}
// Adding c1 to val gives 10 in the top bits for val < 10, 11 for val >= 10
const C1: u32 = 0b11_00000000 - 10; // 758
// Adding c2 to val gives 01 in the top bits for val < 100, 10 for val >= 100
const C2: u32 = 0b10_00000000 - 100; // 412
// 0 < val < 100_000
#[inline]
const fn less_than_5(val: u32) -> u32 {
// Similar to u8, when adding one of these constants to val,
// we get two possible bit patterns above the low 17 bits,
// depending on whether val is below or above the threshold.
const C1: u32 = 0b011_00000000000000000 - 10; // 393206
const C2: u32 = 0b100_00000000000000000 - 100; // 524188
const C3: u32 = 0b111_00000000000000000 - 1000; // 916504
const C4: u32 = 0b100_00000000000000000 - 10000; // 514288
// Value of top bits:
// +c1 +c2 1&2 +c3 +c4 3&4 ^
// 0..=9 010 011 010 110 011 010 000 = 0
// 10..=99 011 011 011 110 011 010 001 = 1
// 100..=999 011 100 000 110 011 010 010 = 2
// 1000..=9999 011 100 000 111 011 011 011 = 3
// 10000..=99999 011 100 000 111 100 100 100 = 4
(((val + C1) & (val + C2)) ^ ((val + C3) & (val + C4))) >> 17
}
// 0 < val <= u16::MAX
#[inline]
pub const fn u16(val: u16) -> u32 {
less_than_5(val as u32)
}
// 0 < val <= u32::MAX
#[inline]
pub const fn u32(mut val: u32) -> u32 {
let mut log = 0;
if val >= 100_000 {
val /= 100_000;
log += 5;
}
log + less_than_5(val)
}
// 0 < val <= u64::MAX
#[inline]
pub const fn u64(mut val: u64) -> u32 {
let mut log = 0;
if val >= 10_000_000_000 {
val /= 10_000_000_000;
log += 10;
}
if val >= 100_000 {
val /= 100_000;
log += 5;
}
log + less_than_5(val as u32)
}
// 0 < val <= u128::MAX
#[inline]
pub const fn u128(mut val: u128) -> u32 {
let mut log = 0;
if val >= 100_000_000_000_000_000_000_000_000_000_000 {
val /= 100_000_000_000_000_000_000_000_000_000_000;
log += 32;
return log + u32(val as u32);
}
if val >= 10_000_000_000_000_000 {
val /= 10_000_000_000_000_000;
log += 16;
}
log + u64(val as u64)
}
// 0 < val <= i8::MAX
#[inline]
pub const fn i8(val: i8) -> u32 {
u8(val as u8)
}
// 0 < val <= i16::MAX
#[inline]
pub const fn i16(val: i16) -> u32 {
u16(val as u16)
}
// 0 < val <= i32::MAX
#[inline]
pub const fn i32(val: i32) -> u32 {
u32(val as u32)
}
// 0 < val <= i64::MAX
#[inline]
pub const fn i64(val: i64) -> u32 {
u64(val as u64)
}
// 0 < val <= i128::MAX
#[inline]
pub const fn i128(val: i128) -> u32 {
u128(val as u128)
}
// Value of top bits:
// +c1 +c2 1&2
// 0..=9 10 01 00 = 0
// 10..=99 11 01 01 = 1
// 100..=255 11 10 10 = 2
((val + C1) & (val + C2)) >> 8
}
macro_rules! impl_checked {
($T:ident) => {
#[inline]
pub const fn $T(val: $T) -> Option<u32> {
if val > 0 { Some(unchecked::$T(val)) } else { None }
}
};
// 0 < val < 100_000
#[inline]
const fn less_than_5(val: u32) -> u32 {
// Similar to u8, when adding one of these constants to val,
// we get two possible bit patterns above the low 17 bits,
// depending on whether val is below or above the threshold.
const C1: u32 = 0b011_00000000000000000 - 10; // 393206
const C2: u32 = 0b100_00000000000000000 - 100; // 524188
const C3: u32 = 0b111_00000000000000000 - 1000; // 916504
const C4: u32 = 0b100_00000000000000000 - 10000; // 514288
// Value of top bits:
// +c1 +c2 1&2 +c3 +c4 3&4 ^
// 0..=9 010 011 010 110 011 010 000 = 0
// 10..=99 011 011 011 110 011 010 001 = 1
// 100..=999 011 100 000 110 011 010 010 = 2
// 1000..=9999 011 100 000 111 011 011 011 = 3
// 10000..=99999 011 100 000 111 100 100 100 = 4
(((val + C1) & (val + C2)) ^ ((val + C3) & (val + C4))) >> 17
}
impl_checked! { u8 }
impl_checked! { u16 }
impl_checked! { u32 }
impl_checked! { u64 }
impl_checked! { u128 }
impl_checked! { i8 }
impl_checked! { i16 }
impl_checked! { i32 }
impl_checked! { i64 }
impl_checked! { i128 }
// 0 < val <= u16::MAX
#[inline]
pub const fn u16(val: u16) -> u32 {
less_than_5(val as u32)
}
// 0 < val <= u32::MAX
#[inline]
pub const fn u32(mut val: u32) -> u32 {
let mut log = 0;
if val >= 100_000 {
val /= 100_000;
log += 5;
}
log + less_than_5(val)
}
// 0 < val <= u64::MAX
#[inline]
pub const fn u64(mut val: u64) -> u32 {
let mut log = 0;
if val >= 10_000_000_000 {
val /= 10_000_000_000;
log += 10;
}
if val >= 100_000 {
val /= 100_000;
log += 5;
}
log + less_than_5(val as u32)
}
// 0 < val <= u128::MAX
#[inline]
pub const fn u128(mut val: u128) -> u32 {
let mut log = 0;
if val >= 100_000_000_000_000_000_000_000_000_000_000 {
val /= 100_000_000_000_000_000_000_000_000_000_000;
log += 32;
return log + u32(val as u32);
}
if val >= 10_000_000_000_000_000 {
val /= 10_000_000_000_000_000;
log += 16;
}
log + u64(val as u64)
}
#[cfg(target_pointer_width = "16")]
#[inline]
pub const fn usize(val: usize) -> u32 {
u16(val as _)
}
#[cfg(target_pointer_width = "32")]
#[inline]
pub const fn usize(val: usize) -> u32 {
u32(val as _)
}
#[cfg(target_pointer_width = "64")]
#[inline]
pub const fn usize(val: usize) -> u32 {
u64(val as _)
}
// 0 < val <= i8::MAX
#[inline]
pub const fn i8(val: i8) -> u32 {
u8(val as u8)
}
// 0 < val <= i16::MAX
#[inline]
pub const fn i16(val: i16) -> u32 {
u16(val as u16)
}
// 0 < val <= i32::MAX
#[inline]
pub const fn i32(val: i32) -> u32 {
u32(val as u32)
}
// 0 < val <= i64::MAX
#[inline]
pub const fn i64(val: i64) -> u32 {
u64(val as u64)
}
// 0 < val <= i128::MAX
#[inline]
pub const fn i128(val: i128) -> u32 {
u128(val as u128)
}

6
library/core/src/num/int_macros.rs
View file

@ -2362,7 +2362,11 @@ macro_rules! int_impl {
without modifying the original"]
#[inline]
pub const fn checked_log10(self) -> Option<u32> {
int_log10::$ActualT(self as $ActualT)
if self > 0 {
Some(int_log10::$ActualT(self as $ActualT))
} else {
None
}
}
/// Computes the absolute value of `self`.

16
library/core/src/num/mod.rs
View file

@ -264,7 +264,7 @@ const ASCII_CASE_MASK: u8 = 0b0010_0000;
#[lang = "u8"]
impl u8 {
uint_impl! { u8, u8, i8, 8, 255, 2, "0x82", "0xa", "0x12", "0x12", "0x48", "[0x12]",
uint_impl! { u8, u8, i8, NonZeroU8, 8, 255, 2, "0x82", "0xa", "0x12", "0x12", "0x48", "[0x12]",
"[0x12]", "", "" }
widening_impl! { u8, u16, 8, unsigned }
@ -813,21 +813,21 @@ impl u8 {
#[lang = "u16"]
impl u16 {
uint_impl! { u16, u16, i16, 16, 65535, 4, "0xa003", "0x3a", "0x1234", "0x3412", "0x2c48",
uint_impl! { u16, u16, i16, NonZeroU16, 16, 65535, 4, "0xa003", "0x3a", "0x1234", "0x3412", "0x2c48",
"[0x34, 0x12]", "[0x12, 0x34]", "", "" }
widening_impl! { u16, u32, 16, unsigned }
}
#[lang = "u32"]
impl u32 {
uint_impl! { u32, u32, i32, 32, 4294967295, 8, "0x10000b3", "0xb301", "0x12345678",
uint_impl! { u32, u32, i32, NonZeroU32, 32, 4294967295, 8, "0x10000b3", "0xb301", "0x12345678",
"0x78563412", "0x1e6a2c48", "[0x78, 0x56, 0x34, 0x12]", "[0x12, 0x34, 0x56, 0x78]", "", "" }
widening_impl! { u32, u64, 32, unsigned }
}
#[lang = "u64"]
impl u64 {
uint_impl! { u64, u64, i64, 64, 18446744073709551615, 12, "0xaa00000000006e1", "0x6e10aa",
uint_impl! { u64, u64, i64, NonZeroU64, 64, 18446744073709551615, 12, "0xaa00000000006e1", "0x6e10aa",
"0x1234567890123456", "0x5634129078563412", "0x6a2c48091e6a2c48",
"[0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
"[0x12, 0x34, 0x56, 0x78, 0x90, 0x12, 0x34, 0x56]",
@ -837,7 +837,7 @@ impl u64 {
#[lang = "u128"]
impl u128 {
uint_impl! { u128, u128, i128, 128, 340282366920938463463374607431768211455, 16,
uint_impl! { u128, u128, i128, NonZeroU128, 128, 340282366920938463463374607431768211455, 16,
"0x13f40000000000000000000000004f76", "0x4f7613f4", "0x12345678901234567890123456789012",
"0x12907856341290785634129078563412", "0x48091e6a2c48091e6a2c48091e6a2c48",
"[0x12, 0x90, 0x78, 0x56, 0x34, 0x12, 0x90, 0x78, \
@ -850,7 +850,7 @@ impl u128 {
#[cfg(target_pointer_width = "16")]
#[lang = "usize"]
impl usize {
uint_impl! { usize, u16, isize, 16, 65535, 4, "0xa003", "0x3a", "0x1234", "0x3412", "0x2c48",
uint_impl! { usize, u16, isize, NonZeroUsize, 16, 65535, 4, "0xa003", "0x3a", "0x1234", "0x3412", "0x2c48",
"[0x34, 0x12]", "[0x12, 0x34]",
usize_isize_to_xe_bytes_doc!(), usize_isize_from_xe_bytes_doc!() }
widening_impl! { usize, u32, 16, unsigned }
@ -858,7 +858,7 @@ impl usize {
#[cfg(target_pointer_width = "32")]
#[lang = "usize"]
impl usize {
uint_impl! { usize, u32, isize, 32, 4294967295, 8, "0x10000b3", "0xb301", "0x12345678",
uint_impl! { usize, u32, isize, NonZeroUsize, 32, 4294967295, 8, "0x10000b3", "0xb301", "0x12345678",
"0x78563412", "0x1e6a2c48", "[0x78, 0x56, 0x34, 0x12]", "[0x12, 0x34, 0x56, 0x78]",
usize_isize_to_xe_bytes_doc!(), usize_isize_from_xe_bytes_doc!() }
widening_impl! { usize, u64, 32, unsigned }
@ -867,7 +867,7 @@ impl usize {
#[cfg(target_pointer_width = "64")]
#[lang = "usize"]
impl usize {
uint_impl! { usize, u64, isize, 64, 18446744073709551615, 12, "0xaa00000000006e1", "0x6e10aa",
uint_impl! { usize, u64, isize, NonZeroUsize, 64, 18446744073709551615, 12, "0xaa00000000006e1", "0x6e10aa",
"0x1234567890123456", "0x5634129078563412", "0x6a2c48091e6a2c48",
"[0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
"[0x12, 0x34, 0x56, 0x78, 0x90, 0x12, 0x34, 0x56]",

52
library/core/src/num/nonzero.rs
View file

@ -302,7 +302,7 @@ nonzero_integers_div! {
// A bunch of methods for unsigned nonzero types only.
macro_rules! nonzero_unsigned_operations {
( $( $Ty: ident($Int: ty); )+ ) => {
( $( $Ty: ident($Int: ident); )+ ) => {
$(
impl $Ty {
/// Add an unsigned integer to a non-zero value.
@ -442,6 +442,56 @@ macro_rules! nonzero_unsigned_operations {
None
}
}
/// Returns the base 2 logarithm of the number, rounded down.
///
/// This is the same operation as
#[doc = concat!("[`", stringify!($Int), "::log2`],")]
/// except that it has no failure cases to worry about
/// since this value can never be zero.
///
/// # Examples
///
/// ```
/// #![feature(int_log)]
#[doc = concat!("# use std::num::", stringify!($Ty), ";")]
///
#[doc = concat!("assert_eq!(", stringify!($Ty), "::new(7).unwrap().log2(), 2);")]
#[doc = concat!("assert_eq!(", stringify!($Ty), "::new(8).unwrap().log2(), 3);")]
#[doc = concat!("assert_eq!(", stringify!($Ty), "::new(9).unwrap().log2(), 3);")]
/// ```
#[unstable(feature = "int_log", issue = "70887")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub const fn log2(self) -> u32 {
<$Int>::BITS - 1 - self.leading_zeros()
}
/// Returns the base 10 logarithm of the number, rounded down.
///
/// This is the same operation as
#[doc = concat!("[`", stringify!($Int), "::log10`],")]
/// except that it has no failure cases to worry about
/// since this value can never be zero.
///
/// # Examples
///
/// ```
/// #![feature(int_log)]
#[doc = concat!("# use std::num::", stringify!($Ty), ";")]
///
#[doc = concat!("assert_eq!(", stringify!($Ty), "::new(99).unwrap().log10(), 1);")]
#[doc = concat!("assert_eq!(", stringify!($Ty), "::new(100).unwrap().log10(), 2);")]
#[doc = concat!("assert_eq!(", stringify!($Ty), "::new(101).unwrap().log10(), 2);")]
/// ```
#[unstable(feature = "int_log", issue = "70887")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub const fn log10(self) -> u32 {
super::int_log10::$Int(self.0)
}
}
)+
}

17
library/core/src/num/uint_macros.rs
View file

@ -1,5 +1,6 @@
macro_rules! uint_impl {
($SelfT:ty, $ActualT:ident, $SignedT:ident, $BITS:expr, $MaxV:expr,
($SelfT:ty, $ActualT:ident, $SignedT:ident, $NonZeroT:ident,
$BITS:expr, $MaxV:expr,
$rot:expr, $rot_op:expr, $rot_result:expr, $swap_op:expr, $swapped:expr,
$reversed:expr, $le_bytes:expr, $be_bytes:expr,
$to_xe_bytes_doc:expr, $from_xe_bytes_doc:expr) => {
@ -839,12 +840,10 @@ macro_rules! uint_impl {
without modifying the original"]
#[inline]
pub const fn checked_log2(self) -> Option<u32> {
if self <= 0 {
None
if let Some(x) = <$NonZeroT>::new(self) {
Some(x.log2())
} else {
// SAFETY: We just checked that this number is positive
let log = (Self::BITS - 1) - unsafe { intrinsics::ctlz_nonzero(self) as u32 };
Some(log)
None
}
}
@ -863,7 +862,11 @@ macro_rules! uint_impl {
without modifying the original"]
#[inline]
pub const fn checked_log10(self) -> Option<u32> {
int_log10::$ActualT(self as $ActualT)
if let Some(x) = <$NonZeroT>::new(self) {
Some(x.log10())
} else {
None
}
}
/// Checked negation. Computes `-self`, returning `None` unless `self ==