Out-of-bounds read

Incorrect values read from a different memory region will cause incorrect computations. Out-of-bounds read from a buffer
/src/mongo/db/storage/key_string.cpp:946: OVERRUN 140316 Function call "mongo::countLeadingZeros64(integerPart << 1)" may return 64.
/src/mongo/db/storage/key_string.cpp:946: OVERRUN 140316 Assigning: "fractionalBytes" = "mongo::countLeadingZeros64(integerPart << 1) / 8". The value of "fractionalBytes" is now 8.
/src/mongo/db/storage/key_string.cpp:953: OVERRUN 140316 Overrunning array "mongo::key_string::<unnamed>::kPow256" of 8 8-byte elements at element index 8 (byte offset 71) using index "fractionalBytes" (which evaluates to 8).