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Rollup merge of #92956 - scottmcm:nonzero-log2, r=dtolnay
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.)
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,141 +1,140 @@ | ||
| mod unchecked { | ||
| // 0 < val <= u8::MAX | ||
| #[inline] | ||
| pub const fn u8(val: u8) -> u32 { | ||
| let val = val as u32; | ||
|
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| // For better performance, avoid branches by assembling the solution | ||
| // in the bits above the low 8 bits. | ||
|
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| // 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 | ||
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| // 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. | ||
|
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||
| // 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 | ||
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||
| // 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 | ||
| } | ||
|
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||
| // 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 | ||
|
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||
| // 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 | ||
|
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||
| // 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 | ||
| } | ||
|
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||
| // 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) | ||
| } | ||
|
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||
| // 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) | ||
| } | ||
|
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||
| // 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; | ||
| } | ||
|
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||
| // 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) | ||
| } |
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