1use super::imp::{BitMaskWord, BITMASK_MASK, BITMASK_STRIDE};
2#[cfg(feature = "nightly")]
3use core::intrinsics;
4
5/// A bit mask which contains the result of a `Match` operation on a `Group` and
6/// allows iterating through them.
7///
8/// The bit mask is arranged so that low-order bits represent lower memory
9/// addresses for group match results.
10///
11/// For implementation reasons, the bits in the set may be sparsely packed, so
12/// that there is only one bit-per-byte used (the high bit, 7). If this is the
13/// case, `BITMASK_STRIDE` will be 8 to indicate a divide-by-8 should be
14/// performed on counts/indices to normalize this difference. `BITMASK_MASK` is
15/// similarly a mask of all the actually-used bits.
16#[derive(Copy, Clone)]
17pub struct BitMask(pub BitMaskWord);
18
19#[allow(clippy::use_self)]
20impl BitMask {
21 /// Returns a new `BitMask` with all bits inverted.
22 #[inline]
23 #[must_use]
24 pub fn invert(self) -> Self {
25 BitMask(self.0 ^ BITMASK_MASK)
26 }
27
28 /// Flip the bit in the mask for the entry at the given index.
29 ///
30 /// Returns the bit's previous state.
31 #[inline]
32 #[allow(clippy::cast_ptr_alignment)]
33 #[cfg(feature = "raw")]
34 pub unsafe fn flip(&mut self, index: usize) -> bool {
35 // NOTE: The + BITMASK_STRIDE - 1 is to set the high bit.
36 let mask = 1 << (index * BITMASK_STRIDE + BITMASK_STRIDE - 1);
37 self.0 ^= mask;
38 // The bit was set if the bit is now 0.
39 self.0 & mask == 0
40 }
41
42 /// Returns a new `BitMask` with the lowest bit removed.
43 #[inline]
44 #[must_use]
45 pub fn remove_lowest_bit(self) -> Self {
46 BitMask(self.0 & (self.0 - 1))
47 }
48 /// Returns whether the `BitMask` has at least one set bit.
49 #[inline]
50 pub fn any_bit_set(self) -> bool {
51 self.0 != 0
52 }
53
54 /// Returns the first set bit in the `BitMask`, if there is one.
55 #[inline]
56 pub fn lowest_set_bit(self) -> Option<usize> {
57 if self.0 == 0 {
58 None
59 } else {
60 Some(unsafe { self.lowest_set_bit_nonzero() })
61 }
62 }
63
64 /// Returns the first set bit in the `BitMask`, if there is one. The
65 /// bitmask must not be empty.
66 #[inline]
67 #[cfg(feature = "nightly")]
68 pub unsafe fn lowest_set_bit_nonzero(self) -> usize {
69 intrinsics::cttz_nonzero(self.0) as usize / BITMASK_STRIDE
70 }
71 #[inline]
72 #[cfg(not(feature = "nightly"))]
73 pub unsafe fn lowest_set_bit_nonzero(self) -> usize {
74 self.trailing_zeros()
75 }
76
77 /// Returns the number of trailing zeroes in the `BitMask`.
78 #[inline]
79 pub fn trailing_zeros(self) -> usize {
80 // ARM doesn't have a trailing_zeroes instruction, and instead uses
81 // reverse_bits (RBIT) + leading_zeroes (CLZ). However older ARM
82 // versions (pre-ARMv7) don't have RBIT and need to emulate it
83 // instead. Since we only have 1 bit set in each byte on ARM, we can
84 // use swap_bytes (REV) + leading_zeroes instead.
85 if cfg!(target_arch = "arm") && BITMASK_STRIDE % 8 == 0 {
86 self.0.swap_bytes().leading_zeros() as usize / BITMASK_STRIDE
87 } else {
88 self.0.trailing_zeros() as usize / BITMASK_STRIDE
89 }
90 }
91
92 /// Returns the number of leading zeroes in the `BitMask`.
93 #[inline]
94 pub fn leading_zeros(self) -> usize {
95 self.0.leading_zeros() as usize / BITMASK_STRIDE
96 }
97}
98
99impl IntoIterator for BitMask {
100 type Item = usize;
101 type IntoIter = BitMaskIter;
102
103 #[inline]
104 fn into_iter(self) -> BitMaskIter {
105 BitMaskIter(self)
106 }
107}
108
109/// Iterator over the contents of a `BitMask`, returning the indices of set
110/// bits.
111pub struct BitMaskIter(BitMask);
112
113impl Iterator for BitMaskIter {
114 type Item = usize;
115
116 #[inline]
117 fn next(&mut self) -> Option<usize> {
118 let bit: usize = self.0.lowest_set_bit()?;
119 self.0 = self.0.remove_lowest_bit();
120 Some(bit)
121 }
122}
123