From 32ea2d74dedb111f643ee65de1f64a972dd3788f Mon Sep 17 00:00:00 2001
From: Dirk Farin <dirk.farin@gmail.com>
Date: Thu, 19 Dec 2024 00:25:39 +0100
Subject: [PATCH] explicitly check precondition when scaling chroma sizes

---
 libheif/common_utils.cc | 30 ++++++++++++++++++++++++------
 libheif/common_utils.h  | 10 ++++++++--
 libheif/pixelimage.cc   |  8 ++++----
 3 files changed, 36 insertions(+), 12 deletions(-)

diff --git a/libheif/common_utils.cc b/libheif/common_utils.cc
index 1751e2d21f..649738527a 100644
--- a/libheif/common_utils.cc
+++ b/libheif/common_utils.cc
@@ -65,14 +65,23 @@ uint8_t chroma_v_subsampling(heif_chroma c)
 uint32_t get_subsampled_size_h(uint32_t width,
                                heif_channel channel,
                                heif_chroma chroma,
-                               bool round_up)
+                               scaling_mode mode)
 {
   if (channel == heif_channel_Cb ||
       channel == heif_channel_Cr) {
     uint8_t chromaSubH = chroma_h_subsampling(chroma);
 
-    // NOLINTNEXTLINE(clang-analyzer-core.DivideZero)
-    return (width + (round_up ? chromaSubH - 1 : 0)) / chromaSubH;
+    switch (mode) {
+      case scaling_mode::round_up:
+        // NOLINTNEXTLINE(clang-analyzer-core.DivideZero)
+        return (width + chromaSubH - 1) / chromaSubH;
+      case scaling_mode::round_down:
+        // NOLINTNEXTLINE(clang-analyzer-core.DivideZero)
+        return width / chromaSubH;
+      case scaling_mode::is_divisible:
+        assert(width % chromaSubH == 0);
+        return width / chromaSubH;
+    }
   } else {
     return width;
   }
@@ -81,14 +90,23 @@ uint32_t get_subsampled_size_h(uint32_t width,
 uint32_t get_subsampled_size_v(uint32_t height,
                                heif_channel channel,
                                heif_chroma chroma,
-                               bool round_up)
+                               scaling_mode mode)
 {
   if (channel == heif_channel_Cb ||
       channel == heif_channel_Cr) {
     uint8_t chromaSubV = chroma_v_subsampling(chroma);
 
-    // NOLINTNEXTLINE(clang-analyzer-core.DivideZero)
-    return (height + (round_up ? chromaSubV - 1 : 0)) / chromaSubV;
+    switch (mode) {
+      case scaling_mode::round_up:
+        // NOLINTNEXTLINE(clang-analyzer-core.DivideZero)
+        return (height + chromaSubV - 1) / chromaSubV;
+      case scaling_mode::round_down:
+        // NOLINTNEXTLINE(clang-analyzer-core.DivideZero)
+        return height / chromaSubV;
+      case scaling_mode::is_divisible:
+        assert(height % chromaSubV == 0);
+        return height / chromaSubV;
+    }
   } else {
     return height;
   }
diff --git a/libheif/common_utils.h b/libheif/common_utils.h
index 159646f9bc..928a166821 100644
--- a/libheif/common_utils.h
+++ b/libheif/common_utils.h
@@ -49,15 +49,21 @@ uint8_t chroma_h_subsampling(heif_chroma c);
 
 uint8_t chroma_v_subsampling(heif_chroma c);
 
+enum class scaling_mode : uint8_t {
+  round_down,
+  round_up,
+  is_divisible
+};
+
 uint32_t get_subsampled_size_h(uint32_t width,
                                heif_channel channel,
                                heif_chroma chroma,
-                               bool round_up);
+                               scaling_mode mode);
 
 uint32_t get_subsampled_size_v(uint32_t height,
                                heif_channel channel,
                                heif_chroma chroma,
-                               bool round_up);
+                               scaling_mode mode);
 
 void get_subsampled_size(uint32_t width, uint32_t height,
                          heif_channel channel,
diff --git a/libheif/pixelimage.cc b/libheif/pixelimage.cc
index 461bd5e28a..453b3ae9b4 100644
--- a/libheif/pixelimage.cc
+++ b/libheif/pixelimage.cc
@@ -1050,10 +1050,10 @@ Result<std::shared_ptr<HeifPixelImage>> HeifPixelImage::crop(uint32_t left, uint
     heif_channel channel = plane_pair.first;
     const ImagePlane& plane = plane_pair.second;
 
-    uint32_t plane_left = get_subsampled_size_h(left, channel, m_chroma, false); // is always divisible
-    uint32_t plane_right = get_subsampled_size_h(right, channel, m_chroma, true); // keep more chroma
-    uint32_t plane_top = get_subsampled_size_v(top, channel, m_chroma, false); // is always divisible
-    uint32_t plane_bottom = get_subsampled_size_v(bottom, channel, m_chroma, true); // keep more chroma
+    uint32_t plane_left = get_subsampled_size_h(left, channel, m_chroma, scaling_mode::is_divisible);
+    uint32_t plane_right = get_subsampled_size_h(right, channel, m_chroma, scaling_mode::round_up); // keep more chroma
+    uint32_t plane_top = get_subsampled_size_v(top, channel, m_chroma, scaling_mode::is_divisible); // is always divisible
+    uint32_t plane_bottom = get_subsampled_size_v(bottom, channel, m_chroma, scaling_mode::round_up); // keep more chroma
 
     auto err = out_img->add_channel(channel,
                                     plane_right - plane_left + 1,