Merge pull request #8694 from mschoeneck:Canny

Parallelize Canny with custom gradient (#8694)

* New Canny implementation. Restructuring code in parallelCanny class. Align mag buffer and map.

* Fix warnings.

* Missing SIMD check added.

* Replaced local trailingZeros in contours.cpp. Use alignSize in canny.cpp

* Fix warnings in alignSize and allocate just minimum extra columns.

* Fix another warning in map.create.

* Exchange for loop by do loop to avoid double check at the beginning.
Define extra SIMD CANNY_CHECK to avoid unnecessary continue.

modules/core/include/opencv2/core/hal/intrin.hpp

@@ -433,6 +433,29 @@ template <> struct V_RegTrait128<double> {
 };
 #endif
 
+inline unsigned int trailingZeros32(unsigned int value) {
+#if defined(_MSC_VER)
+#if (_MSC_VER < 1700)
+    unsigned long index = 0;
+    _BitScanForward(&index, value);
+    return (unsigned int)index;
+#else
+    return _tzcnt_u32(value);
+#endif
+#elif defined(__GNUC__) || defined(__GNUG__)
+    return __builtin_ctz(value);
+#elif defined(__ICC) || defined(__INTEL_COMPILER)
+    return _bit_scan_forward(value);
+#elif defined(__clang__)
+    return llvm.cttz.i32(value, true);
+#else
+    static const int MultiplyDeBruijnBitPosition[32] = {
+        0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
+        31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9 };
+    return MultiplyDeBruijnBitPosition[((uint32_t)((value & -value) * 0x077CB531U)) >> 27];
+#endif
+}
+
 #ifndef CV_DOXYGEN
 CV_CPU_OPTIMIZATION_HAL_NAMESPACE_END
 #endif