@@ -15,7 +15,11 @@ internal sealed class MiniFatChainEnumerator : ContextBase, IEnumerator<uint>
1515uint index = uint . MaxValue ;
1616private uint current = uint . MaxValue ;
1717private long length = - 1 ;
18- private uint slow = uint . MaxValue ; // Floyd's cycle-finding algorithm
18+
19+ // Brent's cycle-finding algorithm
20+ private uint cycleLength = 1 ;
21+ private uint power = 1 ;
22+ private uint slow = uint . MaxValue ;
1923
2024public MiniFatChainEnumerator ( RootContextSite rootContextSite , uint startSectorId )
2125: base ( rootContextSite )
@@ -66,23 +70,27 @@ public bool MoveNext()
6670{
6771index = uint . MaxValue ;
6872current = uint . MaxValue ;
73+ slow = uint . MaxValue ;
6974return false ;
7075}
7176
7277uint nextIndex = index + 1 ;
7378if ( nextIndex > SectorType . Maximum )
7479throw new FileFormatException ( "Mini FAT chain length is greater than the maximum." ) ;
7580
76- if ( nextIndex % 2 == 0 && ! SectorType . IsFreeOrEndOfChain ( slow ) )
81+ if ( value == slow )
82+ throw new FileFormatException ( "Mini FAT chain contains a loop." ) ;
83+
84+ if ( cycleLength == power )
7785{
78- // Slow might become free or end of chain while shrinking
79- slow = Context . MiniFat [ slow ] ;
80- if ( slow == value )
81- throw new FileFormatException ( "Mini FAT chain contains a loop." ) ;
86+ cycleLength = 0 ;
87+ power *= 2 ;
88+ slow = value ;
8289}
8390
8491index = nextIndex ;
8592current = value ;
93+ cycleLength ++ ;
8694return true ;
8795}
8896
@@ -213,6 +221,8 @@ public void Reset()
213221index = uint . MaxValue ;
214222current = uint . MaxValue ;
215223slow = uint . MaxValue ;
224+ cycleLength = 1 ;
225+ power = 1 ;
216226}
217227
218228[ ExcludeFromCodeCoverage ]