options/ansi: fix ftell behaviour after ungetc

Fixes the failing GMP tests documented in managarm#1221.
lzcunt · Jan 28, 2025 · f1a00e7 · f1a00e7
1 parent 1fda4e6
commit f1a00e7
Showing 1 changed file with 3 additions and 1 deletion.
diff --git a/options/ansi/generic/file-io.cpp b/options/ansi/generic/file-io.cpp
@@ -292,7 +292,9 @@ int abstract_file::tell(off_t *current_offset) {
 	if(int e = io_seek(0, SEEK_CUR, &seek_offset); e)
 		return e;
 
-	*current_offset = seek_offset + (off_t(__offset) - off_t(__io_offset));
+	*current_offset = seek_offset
+		+ (off_t(__offset) - off_t(__io_offset))
+		+ (off_t(__unget_ptr) - off_t(__buffer_ptr));
 	return 0;
 }