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[ADT][BitVector][NFC] Merge find_first_in() / find_first_unset_in() 

We can implement find_first_unset_in() in the same function
if every BitWord we use is first flipped.

Differential Revision: https://reviews.llvm.org/D84717
This commit is contained in:
Stefanos Baziotis 2020-07-29 04:51:22 +03:00
parent 00046d789c
commit db0d636e52
1 changed files with 11 additions and 29 deletions
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40
llvm/include/llvm/ADT/BitVector.h
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@ -203,9 +203,10 @@ public:
return !any();
}
/// find_first_in - Returns the index of the first set bit in the range
/// [Begin, End). Returns -1 if all bits in the range are unset.
int find_first_in(unsigned Begin, unsigned End) const {
/// find_first_in - Returns the index of the first set / unset bit,
/// depending on \p Set, in the range [Begin, End).
/// Returns -1 if all bits in the range are unset / set.
int find_first_in(unsigned Begin, unsigned End, bool Set = true) const {
assert(Begin <= End && End <= Size);
if (Begin == End)
return -1;
@ -214,8 +215,14 @@ public:
unsigned LastWord = (End - 1) / BITWORD_SIZE;
// Check subsequent words.
// The code below is based on search for the first _set_ bit. If
// we're searching for the first _unset_, we just take the
// complement of each word before we use it and apply
// the same method.
for (unsigned i = FirstWord; i <= LastWord; ++i) {
BitWord Copy = Bits[i];
if (!Set)
Copy = ~Copy;
if (i == FirstWord) {
unsigned FirstBit = Begin % BITWORD_SIZE;
@ -266,32 +273,7 @@ public:
/// find_first_unset_in - Returns the index of the first unset bit in the
/// range [Begin, End). Returns -1 if all bits in the range are set.
int find_first_unset_in(unsigned Begin, unsigned End) const {
assert(Begin <= End && End <= Size);
if (Begin == End)
return -1;
unsigned FirstWord = Begin / BITWORD_SIZE;
unsigned LastWord = (End - 1) / BITWORD_SIZE;
// Check subsequent words.
for (unsigned i = FirstWord; i <= LastWord; ++i) {
BitWord Copy = Bits[i];
if (i == FirstWord) {
unsigned FirstBit = Begin % BITWORD_SIZE;
Copy |= maskTrailingOnes<BitWord>(FirstBit);
}
if (i == LastWord) {
unsigned LastBit = (End - 1) % BITWORD_SIZE;
Copy |= maskTrailingZeros<BitWord>(LastBit + 1);
}
if (Copy != ~BitWord(0)) {
unsigned Result = i * BITWORD_SIZE + countTrailingOnes(Copy);
return Result < size() ? Result : -1;
}
}
return -1;
return find_first_in(Begin, End, /* Set = */ false);
}
/// find_last_unset_in - Returns the index of the last unset bit in the