Fixed incorrect CBaseSplitterFile::BitRead function on x64.

1 files changed, 8 insertions, 1 deletions

diff --git a/src/filters/parser/BaseSplitter/BaseSplitterFile.cpp b/src/filters/parser/BaseSplitter/BaseSplitterFile.cpp
index 4bc7c0e51..ed40990be 100644
--- a/src/filters/parser/BaseSplitter/BaseSplitterFile.cpp
+++ b/src/filters/parser/BaseSplitter/BaseSplitterFile.cpp
@@ -189,7 +189,14 @@ UINT64 CBaseSplitterFile::BitRead(int nBits, bool fPeek)
 

     int bitlen = m_bitlen - nBits;

 

-    UINT64 ret = (m_bitbuff >> bitlen) & ((1ui64 << nBits) - 1);

+    UINT64 ret;

+    // The shift to 64 bits can give incorrect results.

+    // "The behavior is undefined if the right operand is negative, or greater than or equal to the length in bits of the promoted left operand."

+    if (nBits == 64) {

+        ret = m_bitbuff;

+    } else {

+        ret = (m_bitbuff >> bitlen) & ((1ui64 << nBits) - 1);

+    }

 

     if (!fPeek) {

         m_bitbuff &= ((1ui64 << bitlen) - 1);