From d1da265a2c343f388c70011c4cb90ca37932a261 Mon Sep 17 00:00:00 2001
From: NiDU-NINJA <alnida1505@gmail.com>
Date: Fri, 27 Feb 2026 10:40:09 +0000
Subject: [PATCH 1/2] This PR replaces the use of ftell() with platform-correct
 64-bit file APIs when determining file size in avifIOCreateFileReader().

---
 src/io.c | 37 ++++++++++++++++++++++++++++++++-----
 1 file changed, 32 insertions(+), 5 deletions(-)

diff --git a/src/io.c b/src/io.c
index e43bdb5f2e..d632d148d4 100644
--- a/src/io.c
+++ b/src/io.c
@@ -142,13 +142,40 @@ avifIO * avifIOCreateFileReader(const char * filename)
         return NULL;
     }
 
-    fseek(f, 0, SEEK_END);
-    long fileSize = ftell(f);
-    if (fileSize < 0) {
+#if defined(_WIN32)
+    // Windows uses _fseeki64 / _ftelli64 for large file support
+    if (_fseeki64(f, 0, SEEK_END) != 0) {
         fclose(f);
         return NULL;
     }
-    fseek(f, 0, SEEK_SET);
+    __int64 fileSizeSigned = _ftelli64(f);
+    if (fileSizeSigned < 0) {
+        fclose(f);
+        return NULL;
+    }
+    if (_fseeki64(f, 0, SEEK_SET) != 0) {
+        fclose(f);
+        return NULL;
+    }
+    uint64_t fileSize = (uint64_t)fileSizeSigned;
+
+#else
+    // POSIX large file support
+    if (fseeko(f, 0, SEEK_END) != 0) {
+        fclose(f);
+        return NULL;
+    }
+    off_t fileSizeSigned = ftello(f);
+    if (fileSizeSigned < 0) {
+        fclose(f);
+        return NULL;
+    }
+    if (fseeko(f, 0, SEEK_SET) != 0) {
+        fclose(f);
+        return NULL;
+    }
+    uint64_t fileSize = (uint64_t)fileSizeSigned;
+#endif
 
     avifIOFileReader * reader = (avifIOFileReader *)avifAlloc(sizeof(avifIOFileReader));
     if (!reader) {
@@ -159,7 +186,7 @@ avifIO * avifIOCreateFileReader(const char * filename)
     reader->f = f;
     reader->io.destroy = avifIOFileReaderDestroy;
     reader->io.read = avifIOFileReaderRead;
-    reader->io.sizeHint = (uint64_t)fileSize;
+    reader->io.sizeHint = fileSize;
     reader->io.persistent = AVIF_FALSE;
     if (avifRWDataRealloc(&reader->buffer, 1024) != AVIF_RESULT_OK) {
         avifFree(reader);

From f6e890acc5f1d35a16812fed4faace5186d2fc60 Mon Sep 17 00:00:00 2001
From: NiDU-NINJA <alnida1505@gmail.com>
Date: Wed, 4 Mar 2026 10:39:02 +0000
Subject: [PATCH 2/2] deleted blank line

---
 src/io.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/io.c b/src/io.c
index d632d148d4..c3f9ea2d3a 100644
--- a/src/io.c
+++ b/src/io.c
@@ -158,7 +158,6 @@ avifIO * avifIOCreateFileReader(const char * filename)
         return NULL;
     }
     uint64_t fileSize = (uint64_t)fileSizeSigned;
-
 #else
     // POSIX large file support
     if (fseeko(f, 0, SEEK_END) != 0) {