fix a bug in bitv where the undefined bits in small/big bitv values could cause operations to return incorrect results.
This commit is contained in:
Gareth Daniel Smith
parent
5ccd299b15
commit
69d66a702e
@ -19,37 +19,42 @@ export to_str;
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export eq_vec;
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export methods;
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/// a mask that has a 1 for each defined bit in a small_bitv, assuming n bits
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#[inline(always)]
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fn small_mask(nbits: uint) -> u32 {
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(1 << nbits) - 1
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}
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struct small_bitv {
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/// only the lowest nbits of this value are used. the rest is undefined.
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let mut bits: u32;
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new(bits: u32) { self.bits = bits; }
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priv {
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#[inline(always)]
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fn bits_op(right_bits: u32, f: fn(u32, u32) -> u32) -> bool {
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fn bits_op(right_bits: u32, nbits: uint, f: fn(u32, u32) -> u32)
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-> bool {
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let mask = small_mask(nbits);
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let old_b: u32 = self.bits;
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let new_b = f(old_b, right_bits);
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self.bits = new_b;
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old_b != new_b
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mask & old_b != mask & new_b
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}
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}
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#[inline(always)]
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fn union(s: &small_bitv) -> bool {
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self.bits_op(s.bits, |u1, u2| { u1 | u2 })
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fn union(s: &small_bitv, nbits: uint) -> bool {
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self.bits_op(s.bits, nbits, |u1, u2| u1 | u2)
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}
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#[inline(always)]
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fn intersect(s: &small_bitv) -> bool {
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self.bits_op(s.bits, |u1, u2| { u1 & u2 })
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fn intersect(s: &small_bitv, nbits: uint) -> bool {
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self.bits_op(s.bits, nbits, |u1, u2| u1 & u2)
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}
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#[inline(always)]
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fn become(s: &small_bitv) -> bool {
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let old = self.bits;
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self.bits = s.bits;
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old != self.bits
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fn become(s: &small_bitv, nbits: uint) -> bool {
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self.bits_op(s.bits, nbits, |_u1, u2| u2)
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}
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#[inline(always)]
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fn difference(s: &small_bitv) -> bool {
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let old = self.bits;
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self.bits &= !s.bits;
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old != self.bits
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fn difference(s: &small_bitv, nbits: uint) -> bool {
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self.bits_op(s.bits, nbits, |u1, u2| u1 ^ u2)
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}
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#[inline(always)]
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pure fn get(i: uint) -> bool {
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@ -65,38 +70,66 @@ struct small_bitv {
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}
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}
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#[inline(always)]
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fn equals(b: &small_bitv) -> bool { self.bits == b.bits }
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fn equals(b: &small_bitv, nbits: uint) -> bool {
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let mask = small_mask(nbits);
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mask & self.bits == mask & b.bits
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}
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#[inline(always)]
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fn clear() { self.bits = 0; }
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#[inline(always)]
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fn set_all() { self.bits = !0; }
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#[inline(always)]
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fn is_true() -> bool { self.bits == !0 }
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fn is_true(nbits: uint) -> bool {
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small_mask(nbits) & !self.bits == 0
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}
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#[inline(always)]
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fn is_false() -> bool { self.bits == 0 }
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fn is_false(nbits: uint) -> bool {
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small_mask(nbits) & self.bits == 0
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}
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#[inline(always)]
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fn invert() { self.bits = !self.bits; }
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}
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/**
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* a mask that has a 1 for each defined bit in the nth element of a big_bitv,
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* assuming n bits.
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*/
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#[inline(always)]
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fn big_mask(nbits: uint, elem: uint) -> uint {
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let rmd = nbits % uint_bits;
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let nelems = nbits/uint_bits + if rmd == 0 {0} else {1};
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if elem < nelems - 1 || rmd == 0 {
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!0
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} else {
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(1 << rmd) - 1
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}
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}
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struct big_bitv {
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// only mut b/c of clone and lack of other constructor
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// only mut b/c of clone and lack of other constructor
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let mut storage: ~[mut uint];
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new(-storage: ~[mut uint]) {
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self.storage <- storage;
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}
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priv {
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#[inline(always)]
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fn process(b: &big_bitv, op: fn(uint, uint) -> uint) -> bool {
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fn process(b: &big_bitv, nbits: uint, op: fn(uint, uint) -> uint)
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-> bool {
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let len = b.storage.len();
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assert (self.storage.len() == len);
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let mut changed = false;
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do uint::range(0, len) |i| {
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let w0 = self.storage[i];
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let w1 = b.storage[i];
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let w = op(w0, w1);
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if w0 != w unchecked { changed = true; self.storage[i] = w; };
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let mask = big_mask(nbits, i);
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let w0 = self.storage[i] & mask;
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let w1 = b.storage[i] & mask;
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let w = op(w0, w1) & mask;
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if w0 != w unchecked {
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changed = true;
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self.storage[i] = w;
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}
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true
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};
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}
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changed
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}
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}
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@ -112,15 +145,21 @@ struct big_bitv {
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#[inline(always)]
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fn invert() { for self.each_storage() |w| { w = !w } }
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#[inline(always)]
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fn union(b: &big_bitv) -> bool { self.process(b, lor) }
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fn union(b: &big_bitv, nbits: uint) -> bool {
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self.process(b, nbits, lor)
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}
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#[inline(always)]
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fn intersect(b: &big_bitv) -> bool { self.process(b, land) }
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fn intersect(b: &big_bitv, nbits: uint) -> bool {
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self.process(b, nbits, land)
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}
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#[inline(always)]
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fn become(b: &big_bitv) -> bool { self.process(b, right) }
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fn become(b: &big_bitv, nbits: uint) -> bool {
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self.process(b, nbits, right)
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}
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#[inline(always)]
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fn difference(b: &big_bitv) -> bool {
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fn difference(b: &big_bitv, nbits: uint) -> bool {
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self.invert();
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let b = self.intersect(b);
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let b = self.intersect(b, nbits);
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self.invert();
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b
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}
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@ -140,10 +179,13 @@ struct big_bitv {
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else { self.storage[w] & !flag };
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}
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#[inline(always)]
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fn equals(b: &big_bitv) -> bool {
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fn equals(b: &big_bitv, nbits: uint) -> bool {
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let len = b.storage.len();
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for uint::iterate(0, len) |i| {
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if self.storage[i] != b.storage[i] { return false; }
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let mask = big_mask(nbits, i);
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if mask & self.storage[i] != mask & b.storage[i] {
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return false;
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}
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}
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}
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}
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@ -163,8 +205,10 @@ struct bitv {
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self.rep = small(~small_bitv(if init {!0} else {0}));
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}
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else {
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let s = to_mut(from_elem(nbits / uint_bits + 1,
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if init {!0} else {0}));
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let nelems = nbits/uint_bits +
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if nbits % uint_bits == 0 {0} else {1};
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let elem = if init {!0} else {0};
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let s = to_mut(from_elem(nelems, elem));
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self.rep = big(~big_bitv(s));
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};
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}
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@ -182,20 +226,20 @@ struct bitv {
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match self.rep {
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small(s) => match other.rep {
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small(s1) => match op {
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union => s.union(s1),
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intersect => s.intersect(s1),
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assign => s.become(s1),
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difference => s.difference(s1)
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union => s.union(s1, self.nbits),
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intersect => s.intersect(s1, self.nbits),
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assign => s.become(s1, self.nbits),
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difference => s.difference(s1, self.nbits)
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},
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big(s1) => self.die()
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},
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big(s) => match other.rep {
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small(_) => self.die(),
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big(s1) => match op {
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union => s.union(s1),
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intersect => s.intersect(s1),
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assign => s.become(s1),
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difference => s.difference(s1)
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union => s.union(s1, self.nbits),
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intersect => s.intersect(s1, self.nbits),
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assign => s.become(s1, self.nbits),
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difference => s.difference(s1, self.nbits)
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}
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}
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}
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@ -280,11 +324,11 @@ struct bitv {
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if self.nbits != v1.nbits { return false; }
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match self.rep {
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small(b) => match v1.rep {
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small(b1) => b.equals(b1),
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small(b1) => b.equals(b1, self.nbits),
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_ => false
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},
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big(s) => match v1.rep {
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big(s1) => s.equals(s1),
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big(s1) => s.equals(s1, self.nbits),
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small(_) => return false
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}
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}
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@ -330,7 +374,7 @@ struct bitv {
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#[inline(always)]
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fn is_true() -> bool {
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match self.rep {
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small(b) => b.is_true(),
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small(b) => b.is_true(self.nbits),
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_ => {
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for self.each() |i| { if !i { return false; } }
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true
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@ -351,7 +395,7 @@ struct bitv {
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fn is_false() -> bool {
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match self.rep {
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small(b) => b.is_false(),
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small(b) => b.is_false(self.nbits),
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big(_) => {
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for self.each() |i| { if i { return false; } }
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true
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@ -740,6 +784,33 @@ mod tests {
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let v1 = bitv(110u, false);
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assert !v0.equal(v1);
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}
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#[test]
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fn test_equal_sneaky_small() {
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let a = bitv::bitv(1, false);
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a.set(0, true);
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let b = bitv::bitv(1, true);
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b.set(0, true);
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assert a.equal(b);
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}
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#[test]
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fn test_equal_sneaky_big() {
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let a = bitv::bitv(100, false);
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for uint::range(0, 100) |i| {
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a.set(i, true);
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}
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let b = bitv::bitv(100, true);
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for uint::range(0, 100) |i| {
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b.set(i, true);
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}
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assert a.equal(b);
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}
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}
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//
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