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add some comments on the algorithm

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@33579 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2007-01-27 07:24:51 +00:00
parent 24757decb8
commit 18b69106b7
1 changed files with 20 additions and 1 deletions
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21
include/llvm/ADT/SmallPtrSet.h
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@ -7,7 +7,8 @@
//
//===----------------------------------------------------------------------===//
//
// This file defines the SmallPtrSet class.
// This file defines the SmallPtrSet class. See the doxygen comment for
// SmallPtrSetImpl for more details on the algorithm used.
//
//===----------------------------------------------------------------------===//
@ -19,6 +20,24 @@
namespace llvm {
/// SmallPtrSetImpl - This is the common code shared among all the
/// SmallPtrSet<>'s, which is almost everything. SmallPtrSet has two modes, one
/// for small and one for large sets.
///
/// Small sets use an array of pointers allocated in the SmallPtrSet object,
/// which is treated as a simple array of pointers. When a pointer is added to
/// the set, the array is scanned to see if the element already exists, if not
/// the element is 'pushed back' onto the array. If we run out of space in the
/// array, we grow into the 'large set' case. SmallSet should be used when the
/// sets are often small. In this case, no memory allocation is used, and only
/// light-weight and cache-efficient scanning is used.
///
/// Large sets use a classic exponentially-probed hash table. Empty buckets are
/// represented with an illegal pointer value (-1) to allow null pointers to be
/// inserted. Tombstones are represented with another illegal pointer value
/// (-2), to allow deletion. The hash table is resized when the table is 3/4 or
/// more. When this happens, the table is doubled in size.
///
class SmallPtrSetImpl {
protected:
/// CurArray - This is the current set of buckets. If it points to