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Add log2 and log10 to NonZeroU*
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This version is nice in that it doesn't need to worry about zeros, and thus doesn't have any error cases.
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@scottmcm
scottmcm committed Jan 16, 2022
1 parent 89b9f7b commit 3dfcc66
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Showing 5 changed files with 197 additions and 141 deletions.
247 changes: 123 additions & 124 deletions 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;

// For better performance, avoid branches by assembling the solution
// in the bits above the low 8 bits.

// 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

// 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
}
/// These functions compute the integer logarithm of their type, assuming
/// that someone has already checked that the the value is strictly positive.

// 0 < val <= u8::MAX
#[inline]
pub const fn u8(val: u8) -> u32 {
let val = val as u32;

// For better performance, avoid branches by assembling the solution
// in the bits above the low 8 bits.

// 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

// 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
}

// 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 < 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 <= 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 <= 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 <= 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;
}

// 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)
if val >= 100_000 {
val /= 100_000;
log += 5;
}
log + less_than_5(val as u32)
}

// 0 < val <= i8::MAX
#[inline]
pub const fn i8(val: i8) -> u32 {
u8(val as u8)
// 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);
}

// 0 < val <= i16::MAX
#[inline]
pub const fn i16(val: i16) -> u32 {
u16(val as u16)
if val >= 10_000_000_000_000_000 {
val /= 10_000_000_000_000_000;
log += 16;
}
log + u64(val as u64)
}

// 0 < val <= i32::MAX
#[inline]
pub const fn i32(val: i32) -> u32 {
u32(val as u32)
}
#[cfg(target_pointer_width = "16")]
#[inline]
pub const fn usize(val: usize) -> u32 {
u16(val as _)
}

// 0 < val <= i64::MAX
#[inline]
pub const fn i64(val: i64) -> u32 {
u64(val as u64)
}
#[cfg(target_pointer_width = "32")]
#[inline]
pub const fn usize(val: usize) -> u32 {
u32(val as _)
}

// 0 < val <= i128::MAX
#[inline]
pub const fn i128(val: i128) -> u32 {
u128(val as u128)
}
#[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)
}

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 <= i16::MAX
#[inline]
pub const fn i16(val: i16) -> u32 {
u16(val as u16)
}

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 <= 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 changes: 5 additions & 1 deletion library/core/src/num/int_macros.rs
View file
Expand Up @@ -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`.
Expand Down
16 changes: 8 additions & 8 deletions library/core/src/num/mod.rs
View file
Expand Up @@ -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 }

Expand Down Expand Up @@ -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]",
Expand All @@ -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, \
Expand All @@ -850,15 +850,15 @@ 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 }
}
#[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 }
Expand All @@ -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]",
Expand Down

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