diff options
Diffstat (limited to 'src/int.rs')
| -rw-r--r-- | src/int.rs | 159 |
1 files changed, 159 insertions, 0 deletions
@@ -78,6 +78,22 @@ pub trait PrimInt: /// ``` fn count_zeros(self) -> u32; + /// Returns the number of leading ones in the binary representation + /// of `self`. + /// + /// # Examples + /// + /// ``` + /// use num_traits::PrimInt; + /// + /// let n = 0xF00Du16; + /// + /// assert_eq!(n.leading_ones(), 4); + /// ``` + fn leading_ones(self) -> u32 { + (!self).leading_zeros() + } + /// Returns the number of leading zeros in the binary representation /// of `self`. /// @@ -92,6 +108,22 @@ pub trait PrimInt: /// ``` fn leading_zeros(self) -> u32; + /// Returns the number of trailing ones in the binary representation + /// of `self`. + /// + /// # Examples + /// + /// ``` + /// use num_traits::PrimInt; + /// + /// let n = 0xBEEFu16; + /// + /// assert_eq!(n.trailing_ones(), 4); + /// ``` + fn trailing_ones(self) -> u32 { + (!self).trailing_zeros() + } + /// Returns the number of trailing zeros in the binary representation /// of `self`. /// @@ -218,6 +250,26 @@ pub trait PrimInt: /// ``` fn swap_bytes(self) -> Self; + /// Reverses the order of bits in the integer. + /// + /// The least significant bit becomes the most significant bit, second least-significant bit + /// becomes second most-significant bit, etc. + /// + /// # Examples + /// + /// ``` + /// use num_traits::PrimInt; + /// + /// let n = 0x12345678u32; + /// let m = 0x1e6a2c48u32; + /// + /// assert_eq!(n.reverse_bits(), m); + /// assert_eq!(0u32.reverse_bits(), 0); + /// ``` + fn reverse_bits(self) -> Self { + reverse_bits_fallback(self) + } + /// Convert an integer from big endian to the target's endianness. /// /// On big endian this is a no-op. On little endian the bytes are swapped. @@ -306,6 +358,39 @@ pub trait PrimInt: fn pow(self, exp: u32) -> Self; } +fn one_per_byte<P: PrimInt>() -> P { + // i8, u8: return 0x01 + // i16, u16: return 0x0101 = (0x01 << 8) | 0x01 + // i32, u32: return 0x01010101 = (0x0101 << 16) | 0x0101 + // ... + let mut ret = P::one(); + let mut shift = 8; + let mut b = ret.count_zeros() >> 3; + while b != 0 { + ret = (ret << shift) | ret; + shift <<= 1; + b >>= 1; + } + ret +} + +fn reverse_bits_fallback<P: PrimInt>(i: P) -> P { + let rep_01: P = one_per_byte(); + let rep_03 = (rep_01 << 1) | rep_01; + let rep_05 = (rep_01 << 2) | rep_01; + let rep_0f = (rep_03 << 2) | rep_03; + let rep_33 = (rep_03 << 4) | rep_03; + let rep_55 = (rep_05 << 4) | rep_05; + + // code above only used to determine rep_0f, rep_33, rep_55; + // optimizer should be able to do it in compile time + let mut ret = i.swap_bytes(); + ret = ((ret & rep_0f) << 4) | ((ret >> 4) & rep_0f); + ret = ((ret & rep_33) << 2) | ((ret >> 2) & rep_33); + ret = ((ret & rep_55) << 1) | ((ret >> 1) & rep_55); + ret +} + macro_rules! prim_int_impl { ($T:ty, $S:ty, $U:ty) => { impl PrimInt for $T { @@ -319,11 +404,23 @@ macro_rules! prim_int_impl { <$T>::count_zeros(self) } + #[cfg(has_leading_trailing_ones)] + #[inline] + fn leading_ones(self) -> u32 { + <$T>::leading_ones(self) + } + #[inline] fn leading_zeros(self) -> u32 { <$T>::leading_zeros(self) } + #[cfg(has_leading_trailing_ones)] + #[inline] + fn trailing_ones(self) -> u32 { + <$T>::trailing_ones(self) + } + #[inline] fn trailing_zeros(self) -> u32 { <$T>::trailing_zeros(self) @@ -364,6 +461,12 @@ macro_rules! prim_int_impl { <$T>::swap_bytes(self) } + #[cfg(has_reverse_bits)] + #[inline] + fn reverse_bits(self) -> Self { + <$T>::reverse_bits(self) + } + #[inline] fn from_be(x: Self) -> Self { <$T>::from_be(x) @@ -407,3 +510,59 @@ prim_int_impl!(i64, i64, u64); #[cfg(has_i128)] prim_int_impl!(i128, i128, u128); prim_int_impl!(isize, isize, usize); + +#[cfg(test)] +mod tests { + use int::PrimInt; + + #[test] + pub fn reverse_bits() { + use core::{i16, i32, i64, i8}; + + assert_eq!( + PrimInt::reverse_bits(0x0123_4567_89ab_cdefu64), + 0xf7b3_d591_e6a2_c480 + ); + + assert_eq!(PrimInt::reverse_bits(0i8), 0); + assert_eq!(PrimInt::reverse_bits(-1i8), -1); + assert_eq!(PrimInt::reverse_bits(1i8), i8::MIN); + assert_eq!(PrimInt::reverse_bits(i8::MIN), 1); + assert_eq!(PrimInt::reverse_bits(-2i8), i8::MAX); + assert_eq!(PrimInt::reverse_bits(i8::MAX), -2); + + assert_eq!(PrimInt::reverse_bits(0i16), 0); + assert_eq!(PrimInt::reverse_bits(-1i16), -1); + assert_eq!(PrimInt::reverse_bits(1i16), i16::MIN); + assert_eq!(PrimInt::reverse_bits(i16::MIN), 1); + assert_eq!(PrimInt::reverse_bits(-2i16), i16::MAX); + assert_eq!(PrimInt::reverse_bits(i16::MAX), -2); + + assert_eq!(PrimInt::reverse_bits(0i32), 0); + assert_eq!(PrimInt::reverse_bits(-1i32), -1); + assert_eq!(PrimInt::reverse_bits(1i32), i32::MIN); + assert_eq!(PrimInt::reverse_bits(i32::MIN), 1); + assert_eq!(PrimInt::reverse_bits(-2i32), i32::MAX); + assert_eq!(PrimInt::reverse_bits(i32::MAX), -2); + + assert_eq!(PrimInt::reverse_bits(0i64), 0); + assert_eq!(PrimInt::reverse_bits(-1i64), -1); + assert_eq!(PrimInt::reverse_bits(1i64), i64::MIN); + assert_eq!(PrimInt::reverse_bits(i64::MIN), 1); + assert_eq!(PrimInt::reverse_bits(-2i64), i64::MAX); + assert_eq!(PrimInt::reverse_bits(i64::MAX), -2); + } + + #[test] + #[cfg(has_i128)] + pub fn reverse_bits_i128() { + use core::i128; + + assert_eq!(PrimInt::reverse_bits(0i128), 0); + assert_eq!(PrimInt::reverse_bits(-1i128), -1); + assert_eq!(PrimInt::reverse_bits(1i128), i128::MIN); + assert_eq!(PrimInt::reverse_bits(i128::MIN), 1); + assert_eq!(PrimInt::reverse_bits(-2i128), i128::MAX); + assert_eq!(PrimInt::reverse_bits(i128::MAX), -2); + } +} |