From: Hans Kristian Rosbach <hk-git@circlestorm.org>
Date: Tue, 13 Jan 2026 14:32:53 +0000 (+0100)
Subject: Add Z_UNREACHABLE compiler hint
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e5129cfe46dcd2aa0c679a8f9e169dff69df4f2f;p=thirdparty%2Fzlib-ng.git

Add Z_UNREACHABLE compiler hint
---

diff --git a/deflate.c b/deflate.c
index aa534fb29..a9645ce8e 100644
--- a/deflate.c
+++ b/deflate.c
@@ -711,6 +711,7 @@ unsigned long Z_EXPORT PREFIX(deflateBound)(PREFIX3(stream) *strm, unsigned long
         break;
 #endif
     default:                                /* for compiler happiness */
+        Z_UNREACHABLE();
         wraplen = ZLIB_WRAPLEN;
     }
 
diff --git a/gzread.c b/gzread.c
index d52fea80e..3e321a03b 100644
--- a/gzread.c
+++ b/gzread.c
@@ -232,6 +232,7 @@ static int gz_fetch(gz_state *state) {
                 return -1;
             continue;
         default:    // Can't happen
+            Z_UNREACHABLE();
             return -1;
         }
     } while (state->x.have == 0 && (!state->eof || strm->avail_in));
diff --git a/zbuild.h b/zbuild.h
index 954bad316..b17362767 100644
--- a/zbuild.h
+++ b/zbuild.h
@@ -48,6 +48,17 @@
 #  endif
 #endif
 
+/* Hint to compiler that a block of code is unreachable, typically in a switch default condition */
+#ifndef Z_UNREACHABLE
+#  if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202311L
+#    define Z_UNREACHABLE() unreachable()           // C23 approach
+#  elif (defined(__GNUC__) && (__GNUC__ >= 5)) || defined(__clang__)
+#    define Z_UNREACHABLE() __builtin_unreachable()
+#  else
+#    define Z_UNREACHABLE()
+#  endif
+#endif
+
 #ifndef Z_TARGET
 #  if Z_HAS_ATTRIBUTE(__target__)
 #    define Z_TARGET(x) __attribute__((__target__(x)))