From ed3b54e4eb3cea21099023f685b0908a09e616d0 Mon Sep 17 00:00:00 2001
From: heckflosse <heckflosse67@gmx.de>
Date: Tue, 23 Oct 2018 15:43:24 +0200
Subject: [PATCH] DNG files from DJI FC6310 open extremely slow, fixes #4888

---
 rtengine/dcraw.cc | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/rtengine/dcraw.cc b/rtengine/dcraw.cc
index 73f9c948f..f1e2b73bb 100644
--- a/rtengine/dcraw.cc
+++ b/rtengine/dcraw.cc
@@ -6462,17 +6462,20 @@ guess_cfa_pc:
             unsigned oldOrder = order;
             order = 0x4d4d; // always big endian per definition in https://www.adobe.com/content/dam/acom/en/products/photoshop/pdfs/dng_spec_1.4.0.0.pdf chapter 7
             unsigned ntags = get4(); // read the number of opcodes
-            while (ntags--) {
-              unsigned opcode = get4();
-              fseek (ifp, 8, SEEK_CUR); // skip 8 bytes as they don't interest us currently
-              if (opcode == 4) { // FixBadPixelsConstant
-                fseek (ifp, 4, SEEK_CUR); // skip 4 bytes as we know that the opcode 4 takes 4 byte
-                if(get4() == 0) { // if raw 0 values should be treated as bad pixels, set zero_is_bad to true (1). That's the only value currently supported by rt
-                    zero_is_bad = 1;
+
+            if (ntags < ifp->size / 12) { // rough check for wrong value (happens for example with DNG files from DJI FC6310)
+                while (ntags-- && !ifp->eof) {
+                  unsigned opcode = get4();
+                  fseek (ifp, 8, SEEK_CUR); // skip 8 bytes as they don't interest us currently
+                  if (opcode == 4) { // FixBadPixelsConstant
+                    fseek (ifp, 4, SEEK_CUR); // skip 4 bytes as we know that the opcode 4 takes 4 byte
+                    if(get4() == 0) { // if raw 0 values should be treated as bad pixels, set zero_is_bad to true (1). That's the only value currently supported by rt
+                        zero_is_bad = 1;
+                    }
+                  } else {
+                    fseek (ifp, get4(), SEEK_CUR);
+                  }
                 }
-              } else {
-                fseek (ifp, get4(), SEEK_CUR);
-              }
             }
             order = oldOrder;
           break;