From f0a7bb7bdc77b404c79592be684f3c5d234751cf Mon Sep 17 00:00:00 2001
From: Su Laus <sulau@freenet.de>
Date: Sun, 12 Mar 2023 21:05:56 +0000
Subject: Optimize relative seeking with TIFFSetDirectory

---
 libtiff/tif_dir.c     | 50 +++++++++++++++++++++++++++++++++++++++-----------
 libtiff/tif_dirread.c |  7 ++++++-
 libtiff/tif_open.c    |  1 +
 libtiff/tiffiop.h     |  4 +++-
 4 files changed, 49 insertions(+), 13 deletions(-)

(limited to 'libtiff')

diff --git a/libtiff/tif_dir.c b/libtiff/tif_dir.c
index 56ecbf39..293d6fde 100644
--- a/libtiff/tif_dir.c
+++ b/libtiff/tif_dir.c
@@ -1702,6 +1702,12 @@ int TIFFCreateCustomDirectory(TIFF *tif, const TIFFFieldArray *infoarray)
     tif->tif_curoff = 0;
     tif->tif_row = (uint32_t)-1;
     tif->tif_curstrip = (uint32_t)-1;
+    /* invalidate directory index */
+    tif->tif_curdir = TIFF_NON_EXISTENT_DIR_NUMBER;
+    /* invalidate IFD loop lists */
+    _TIFFCleanupIFDOffsetAndNumberMaps(tif);
+    /* To be able to return from SubIFD or custom-IFD to main-IFD */
+    tif->tif_setdirectory_force_absolute = TRUE;
 
     return 0;
 }
@@ -2022,14 +2028,31 @@ tdir_t TIFFNumberOfDirectories(TIFF *tif)
 int TIFFSetDirectory(TIFF *tif, tdir_t dirn)
 {
     uint64_t nextdiroff;
-    tdir_t nextdirnum;
+    tdir_t nextdirnum = 0;
     tdir_t n;
-
-    if (!(tif->tif_flags & TIFF_BIGTIFF))
+    /* Fast path when we just advance relative to the current directory:
+     * start at the current dir offset and continue to seek from there.
+     * Check special cases when relative is not allowed:
+     * - jump back from SubIFD or custom directory
+     * - right after TIFFWriteDirectory() jump back to that directory
+     *   using TIFFSetDirectory() */
+    const int relative = (dirn >= tif->tif_curdir) && (tif->tif_diroff != 0) &&
+                         !tif->tif_setdirectory_force_absolute;
+
+    if (relative)
+    {
+        nextdiroff = tif->tif_diroff;
+        dirn -= tif->tif_curdir;
+        nextdirnum = tif->tif_curdir;
+    }
+    else if (!(tif->tif_flags & TIFF_BIGTIFF))
         nextdiroff = tif->tif_header.classic.tiff_diroff;
     else
         nextdiroff = tif->tif_header.big.tiff_diroff;
-    nextdirnum = 0;
+
+    /* Reset to relative stepping */
+    tif->tif_setdirectory_force_absolute = FALSE;
+
     for (n = dirn; n > 0 && nextdiroff != 0; n--)
         if (!TIFFAdvanceDirectory(tif, &nextdiroff, NULL, &nextdirnum))
             return (0);
@@ -2039,12 +2062,15 @@ int TIFFSetDirectory(TIFF *tif, tdir_t dirn)
         return (0);
 
     tif->tif_nextdiroff = nextdiroff;
-    /*
-     * Set curdir to the actual directory index.  The
-     * -1 decrement is because TIFFReadDirectory will increment
-     * tif_curdir after successfully reading the directory.
-     */
-    tif->tif_curdir = (dirn - n);
+
+    /* Set curdir to the actual directory index. */
+    if (relative)
+        tif->tif_curdir += dirn - n;
+    else
+        tif->tif_curdir = dirn - n;
+
+    /* The -1 decrement is because TIFFReadDirectory will increment
+     * tif_curdir after successfully reading the directory. */
     if (tif->tif_curdir == 0)
         tif->tif_curdir = TIFF_NON_EXISTENT_DIR_NUMBER;
     else
@@ -2108,6 +2134,8 @@ int TIFFSetSubDirectory(TIFF *tif, uint64_t diroff)
         tif->tif_curdir = 0; /* first directory of new chain */
         /* add this offset to new IFD list */
         _TIFFCheckDirNumberAndOffset(tif, tif->tif_curdir, diroff);
+        /* To be able to return from SubIFD or custom-IFD to main-IFD */
+        tif->tif_setdirectory_force_absolute = TRUE;
     }
     return (retval);
 }
@@ -2250,6 +2278,6 @@ int TIFFUnlinkDirectory(TIFF *tif, tdir_t dirn)
     tif->tif_row = (uint32_t)-1;
     tif->tif_curstrip = (uint32_t)-1;
     tif->tif_curdir = TIFF_NON_EXISTENT_DIR_NUMBER;
-    _TIFFCleanupIFDOffsetAndNumberMaps(tif);
+    _TIFFCleanupIFDOffsetAndNumberMaps(tif); /* invalidate IFD loop lists */
     return (1);
 }
diff --git a/libtiff/tif_dirread.c b/libtiff/tif_dirread.c
index ef21f7f5..d4cc11d0 100644
--- a/libtiff/tif_dirread.c
+++ b/libtiff/tif_dirread.c
@@ -4067,8 +4067,11 @@ int TIFFReadDirectory(TIFF *tif)
 
     if (tif->tif_nextdiroff == 0)
     {
-        /* In this special case, tif_diroff needs also to be set to 0. */
+        /* In this special case, tif_diroff needs also to be set to 0.
+         * Furthermore, TIFFSetDirectory() needs to be switched to
+         * absolute stepping. */
         tif->tif_diroff = tif->tif_nextdiroff;
+        tif->tif_setdirectory_force_absolute = TRUE;
         return 0; /* last offset, thus no checking necessary */
     }
 
@@ -5131,6 +5134,8 @@ int TIFFReadCustomDirectory(TIFF *tif, toff_t diroff,
             } /*-- if (!dp->tdir_ignore) */
         }
     }
+    /* To be able to return from SubIFD or custom-IFD to main-IFD */
+    tif->tif_setdirectory_force_absolute = TRUE;
     if (dir)
         _TIFFfreeExt(tif, dir);
     return 1;
diff --git a/libtiff/tif_open.c b/libtiff/tif_open.c
index e84ef6d2..aa16a64f 100644
--- a/libtiff/tif_open.c
+++ b/libtiff/tif_open.c
@@ -485,6 +485,7 @@ TIFF *TIFFClientOpenExt(const char *name, const char *mode,
             goto bad;
         tif->tif_diroff = 0;
         tif->tif_lastdiroff = 0;
+        tif->tif_setdirectory_force_absolute = FALSE;
         return (tif);
     }
     /*
diff --git a/libtiff/tiffiop.h b/libtiff/tiffiop.h
index c419608d..fbf7b070 100644
--- a/libtiff/tiffiop.h
+++ b/libtiff/tiffiop.h
@@ -148,7 +148,9 @@ struct tiff
     uint64_t tif_lastdiroff; /* file offset of last directory written so far */
     TIFFHashSet *tif_map_dir_offset_to_number;
     TIFFHashSet *tif_map_dir_number_to_offset;
-    TIFFDirectory tif_dir; /* internal rep of current directory */
+    int tif_setdirectory_force_absolute; /* switch between relative and absolute
+                                            stepping in TIFFSetDirectory() */
+    TIFFDirectory tif_dir;               /* internal rep of current directory */
     TIFFDirectory
         tif_customdir; /* custom IFDs are separated from the main ones */
     union
-- 
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