Replace [[fallthrough]] with WEBP_FALLTHROUGH

C and C++ version values based on
https://en.cppreference.com/w/c/23.html and
https://en.cppreference.com/w/cpp/preprocessor/replace.

Change-Id: I1059fa9e17f25f05d452f8dd003ca7d421742bf7

examples/anim_diff.c

@@ -70,8 +70,10 @@ static int FramesAreSimilar(const uint8_t* const rgba1,
   for (j = 0; j < height; ++j) {
     for (i = 0; i < width; ++i) {
       const int stride = width * 4;
-      const size_t offset = j * stride + i;
-      if (!PixelsAreSimilar(rgba1[offset], rgba2[offset], max_allowed_diff)) {
+      size_t offset_row, offset;
+      if (!CheckMultiplicationOverflow(j, stride, &offset_row) ||
+          !CheckAdditionOverflow(offset_row, i, &offset) ||
+          !PixelsAreSimilar(rgba1[offset], rgba2[offset], max_allowed_diff)) {
         return 0;
       }
     }

examples/anim_util.c

@@ -102,10 +102,8 @@ int CheckMultiplicationOverflow(uint32_t val1, uint32_t val2, size_t* product) {
   return 0;
 }
 
-#if defined(WEBP_HAVE_GIF)
-
 WEBP_NODISCARD
-static int CheckAdditionOverflow(size_t val1, uint32_t val2, size_t* addition) {
+int CheckAdditionOverflow(size_t val1, uint32_t val2, size_t* addition) {
   const uint64_t size = (uint64_t)val1 + val2;
   if (CheckSizeForOverflow(size)) {
     *addition = (size_t)size;
@@ -114,6 +112,8 @@ static int CheckAdditionOverflow(size_t val1, uint32_t val2, size_t* addition) {
   return 0;
 }
 
+#if defined(WEBP_HAVE_GIF)
+
 // For the GIF functions below, the width, height, x_offset, y_offset fit on 16
 // bits (but can fill the 16 bits) as per the GIF specification.
 // Multiplications that can overflow are cast to 64 bits.

examples/anim_util.h

@@ -73,6 +73,9 @@ void GetAnimatedImageVersions(int* const decoder_version,
 // Check whether val1 * val2 fits in a size_t. Returns 1 on success.
 int CheckMultiplicationOverflow(uint32_t val1, uint32_t val2, size_t* product);
 
+// Check whether val1 + val2 fits in a size_t. Returns 1 on success.
+int CheckAdditionOverflow(size_t val1, uint32_t val2, size_t* addition);
+
 #ifdef __cplusplus
 }  // extern "C"
 #endif

examples/webpmux.c

@@ -493,12 +493,18 @@ static int ParseFrameArgs(const char* args, WebPMuxFrameInfo* const info) {
                               &plus_minus, &blend_method, &unused);
   switch (num_args) {
     case 1:
-      info->x_offset = info->y_offset = 0;  // fall through
+      info->x_offset = info->y_offset = 0;
+      WEBP_FALLTHROUGH;
+      // fall through
     case 3:
-      dispose_method = 0;  // fall through
+      dispose_method = 0;
+      WEBP_FALLTHROUGH;
+      // fall through
     case 4:
       plus_minus = '+';
-      blend_method = 'b';  // fall through
+      blend_method = 'b';
+      WEBP_FALLTHROUGH;
+      // fall through
     case 6:
       break;
     case 2:

src/mux/muxinternal.c

@@ -500,6 +500,14 @@ WebPMuxError MuxValidate(const WebPMux* const mux) {
   err = ValidateChunk(mux, IDX_XMP, XMP_FLAG, flags, 1, &num_xmp);
   if (err != WEBP_MUX_OK) return err;
 
+  // Verify either VP8X chunk is present OR there is only one elem in
+  // mux->images.
+  err = ValidateChunk(mux, IDX_VP8X, NO_FLAG, flags, 1, &num_vp8x);
+  if (err != WEBP_MUX_OK) return err;
+  err = ValidateChunk(mux, IDX_VP8, NO_FLAG, flags, -1, &num_images);
+  if (err != WEBP_MUX_OK) return err;
+  if (num_vp8x == 0 && num_images != 1) return WEBP_MUX_INVALID_ARGUMENT;
+
   // Animation: ANIMATION_FLAG, ANIM chunk and ANMF chunk(s) are consistent.
   // At most one ANIM chunk.
   err = ValidateChunk(mux, IDX_ANIM, NO_FLAG, flags, 1, &num_anim);
@@ -509,7 +517,10 @@ WebPMuxError MuxValidate(const WebPMux* const mux) {
 
   {
     const int has_animation = !!(flags & ANIMATION_FLAG);
-    if (has_animation && (num_anim == 0 || num_frames == 0)) {
+    // An ANIM chunk must be present when has_animation is true, and all images
+    // must be contained in ANMF chunks.
+    if (has_animation &&
+        (num_anim == 0 || num_frames == 0 || num_frames != num_images)) {
       return WEBP_MUX_INVALID_ARGUMENT;
     }
     if (!has_animation && (num_anim == 1 || num_frames > 0)) {
@@ -531,14 +542,6 @@ WebPMuxError MuxValidate(const WebPMux* const mux) {
     }
   }
 
-  // Verify either VP8X chunk is present OR there is only one elem in
-  // mux->images.
-  err = ValidateChunk(mux, IDX_VP8X, NO_FLAG, flags, 1, &num_vp8x);
-  if (err != WEBP_MUX_OK) return err;
-  err = ValidateChunk(mux, IDX_VP8, NO_FLAG, flags, -1, &num_images);
-  if (err != WEBP_MUX_OK) return err;
-  if (num_vp8x == 0 && num_images != 1) return WEBP_MUX_INVALID_ARGUMENT;
-
   // ALPHA_FLAG & alpha chunk(s) are consistent.
   // Note: ALPHA_FLAG can be set when there is actually no Alpha data present.
   if (MuxHasAlpha(mux->images)) {

src/webp/types.h

@@ -71,6 +71,15 @@ typedef long long int int64_t;
 #endif /* defined(_WIN32) && defined(WEBP_DLL) */
 #endif /* WEBP_EXTERN */
 
+#ifndef WEBP_FALLTHROUGH
+#if (defined(__cplusplus) && __cplusplus >= 201703L) || \
+    (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202311L)
+#define WEBP_FALLTHROUGH [[fallthrough]]
+#else
+#define WEBP_FALLTHROUGH
+#endif
+#endif /* WEBP_FALLTHROUGH */
+
 // Macro to check ABI compatibility (same major revision number)
 #define WEBP_ABI_IS_INCOMPATIBLE(a, b) (((a) >> 8) != ((b) >> 8))