From 8b772e860ad66d5c27d7c69199a008afb69d5c63 Mon Sep 17 00:00:00 2001
From: Vincent Rabaud <vrabaud@google.com>
Date: Fri, 4 Sep 2026 16:12:16 +0200
Subject: [PATCH] Fix potential CPU bomb

The test went from 2.8s to 7ms
---
 modules/imgproc/src/warp_kernels.simd.hpp | 23 ++++++++++++++---------
 modules/imgproc/test/test_imgwarp.cpp     | 10 ++++++++++
 2 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/modules/imgproc/src/warp_kernels.simd.hpp b/modules/imgproc/src/warp_kernels.simd.hpp
index f6cc9a1742..f01c984f9f 100644
--- a/modules/imgproc/src/warp_kernels.simd.hpp
+++ b/modules/imgproc/src/warp_kernels.simd.hpp
@@ -336,17 +336,22 @@ static inline int borderInterpolate_fast( int p, int len, int borderType )
         p = p < 0 ? 0 : len - 1;
     else if( borderType == BORDER_REFLECT || borderType == BORDER_REFLECT_101 )
     {
+        const int delta = borderType == BORDER_REFLECT_101;
         if( len == 1 )
             return 0;
-        int delta = borderType == BORDER_REFLECT_101;
-        do
-        {
-            if( p < 0 )
-                p = -p - 1 + delta;
-            else
-                p = len - 1 - (p - len) - delta;
-        }
-        while( (unsigned)p >= (unsigned)len );
+
+        // Fast path: single reflection without division for small deviations.
+        if( -len + delta <= p && p < 2 * len - delta )
+            return p < 0 ? -p - 1 + delta : 2 * len - 1 - delta - p;
+        // Bounded fallback: O(1) modulo for large |p|
+        const int64 period = 2LL * (len - delta);
+        int64 p64 = p;
+        p64 %= period;
+        if( p64 < 0 )
+            p64 += period;
+        if( p64 >= len )
+            p64 = period - p64 - 1 + delta;
+        p = (int)p64;
     }
     else if( borderType == BORDER_WRAP )
     {
diff --git a/modules/imgproc/test/test_imgwarp.cpp b/modules/imgproc/test/test_imgwarp.cpp
index 4bf0150de3..6b4051c716 100644
--- a/modules/imgproc/test/test_imgwarp.cpp
+++ b/modules/imgproc/test/test_imgwarp.cpp
@@ -1253,5 +1253,15 @@ TEST(Imgproc_Warping, infinite_loop)
         << "cv::warpAffine hung in an infinite loop!";
 }
 
+TEST(Imgproc_Warping, interpolate_loop)
+{
+    // 1000x1000 destination image with out-of-bounds coordinates:
+    cv::Mat src(2, 2, CV_8UC1, cv::Scalar(42));
+    cv::Mat dst;
+    // A perspective or affine transform mapping pixels to large coordinates:
+    cv::Matx23d M(1, 0, 1e7, 0, 1, 1e7);
+    cv::warpAffine(src, dst, M, cv::Size(50, 50), cv::INTER_NEAREST, cv::BORDER_REFLECT_101);
+}
+
 }} // namespace
 /* End of file. */