Handle undefined shifts in CPDF_PSEngine.

core/fpdfapi/page/fpdf_page_func.cpp

Index: core/fpdfapi/page/fpdf_page_func.cpp
diff --git a/core/fpdfapi/page/fpdf_page_func.cpp b/core/fpdfapi/page/fpdf_page_func.cpp
index d2e08a511c6566e583e9f7e29c0221058580ed1c..2efbdc24808f064928da8c7fca9e7606efa83505 100644
--- a/core/fpdfapi/page/fpdf_page_func.cpp
+++ b/core/fpdfapi/page/fpdf_page_func.cpp
@@ -343,11 +343,20 @@ FX_BOOL CPDF_PSEngine::DoOperator(PDF_PSOP op) {
     case PSOP_BITSHIFT: {
       int shift = (int)Pop();
       int i = (int)Pop();
-      if (shift > 0) {
-        Push(i << shift);
-      } else {
-        Push(i >> -shift);
+      if (shift == 0) {
+        Push(i);
+        break;
+      }
+      if (shift < -31 || shift > 31) {
+        Push(0);
+        break;
       }
+      uint64_t unsigned_i = i;

[Tom Sepez, 2016/10/20 20:55:29]

think we want to do it as a signed64?

+      if (shift > 0)
+        unsigned_i <<= shift;
+      else
+        unsigned_i >>= shift;

[Tom Sepez, 2016/10/20 20:55:30]

need a -shift here?

+      Push(static_cast<int>(unsigned_i & 0xFFFFFFFF));
       break;
     }
     case PSOP_TRUE: