lib: avoid clang static analyzer warning in deflate_get_offset_slot()

common_defs.h

@@ -204,6 +204,13 @@ typedef size_t machine_word_t;
 #  define MAYBE_UNUSED
 #endif
 
+/* NORETURN - mark a function as never returning, e.g. due to calling abort() */
+#if defined(__GNUC__) || __has_attribute(noreturn)
+#  define NORETURN		__attribute__((noreturn))
+#else
+#  define NORETURN
+#endif
+
 /*
  * restrict - hint that writes only occur through the given pointer.
  *

lib/deflate_compress.c

@@ -1474,6 +1474,8 @@ deflate_get_offset_slot(u32 offset)
 	 */
 	unsigned n = (256 - offset) >> 29;
 
+	ASSERT(offset >= 1 && offset <= 32768);
+
 	return deflate_offset_slot[(offset - 1) >> n] + (n << 1);
 }
 

lib/lib_common.h

@@ -76,15 +76,23 @@ int memcmp(const void *s1, const void *s2, size_t n);
 
 #undef LIBDEFLATE_ENABLE_ASSERTIONS
 #else
-#include <string.h>
+#  include <string.h>
+   /*
+    * To prevent false positive static analyzer warnings, ensure that assertions
+    * are visible to the static analyzer.
+    */
+#  ifdef __clang_analyzer__
+#    define LIBDEFLATE_ENABLE_ASSERTIONS
+#  endif
 #endif
 
 /*
  * Runtime assertion support.  Don't enable this in production builds; it may
  * hurt performance significantly.
  */
 #ifdef LIBDEFLATE_ENABLE_ASSERTIONS
-void libdeflate_assertion_failed(const char *expr, const char *file, int line);
+NORETURN void
+libdeflate_assertion_failed(const char *expr, const char *file, int line);
 #define ASSERT(expr) { if (unlikely(!(expr))) \
 	libdeflate_assertion_failed(#expr, __FILE__, __LINE__); }
 #else

lib/utils.c

@@ -132,7 +132,7 @@ memcmp(const void *s1, const void *s2, size_t n)
 #ifdef LIBDEFLATE_ENABLE_ASSERTIONS
 #include <stdio.h>
 #include <stdlib.h>
-void
+NORETURN void
 libdeflate_assertion_failed(const char *expr, const char *file, int line)
 {
 	fprintf(stderr, "Assertion failed: %s at %s:%d\n", expr, file, line);

programs/test_util.c

@@ -42,7 +42,7 @@
 #endif
 
 /* Abort with an error message */
-_noreturn void
+NORETURN void
 assertion_failed(const char *expr, const char *file, int line)
 {
 	msg("Assertion failed: %s at %s:%d", expr, file, line);

programs/test_util.h

@@ -32,13 +32,7 @@
 
 #include <zlib.h> /* for comparison purposes */
 
-#if defined(__GNUC__) || __has_attribute(noreturn)
-# define _noreturn __attribute__((noreturn))
-#else
-# define _noreturn
-#endif
-
-void _noreturn
+NORETURN void
 assertion_failed(const char *expr, const char *file, int line);
 
 #define ASSERT(expr) { if (unlikely(!(expr))) \