This pullrequest changes

Introduces cv::util::BufferArea class automating creation of structured memory areas for local memory buffers.

There are two modes: safe and unsafe. In safe mode each allocation is performed immediately, in unsafe mode (default) single large buffer will be allocated during the call to commit and all pointers will be set to appropriate locations inside this buffer. Safe mode can be forced at runtime by constructor parameter for one specific object or using an environment variable for all objects (OPENCV_BUFFER_AREA_ALWAYS_SAFE). Safe mode will also be forced for sanitizer-enabled builds.

Single buffer split into several smaller ones is used in several algorithms to reduce memory allocations for better performance. However this approach does not allow to catch OOB access using valgrind or address sanitizer and is prone to errors in address arithmetic calculations. Proposed class allows fast but unsafe mode by default and slower but safer mode for instrumentation and debugging.

Example of use:

int * buf1 = 0;
double * buf2 = 0;
cv::util::BufferArea area;
area.allocate(buf1, 200); // buf1 = new int[200];
area.allocate(buf2, 1000, 64); // buf2 = new double[1000]; - aligned by 64
area.commit();
// NOTE: area stores references to buf1 and buf2 and effectively owns them

Example of old code doing the same work :

char * buf = malloc(200 * sizeof(int) + 1000 * sizeof(double) + some_alignment_reserve);
int * buf1 = (int*)alignPtr(buf, sizeof(int));
double * buf2 = (double*)alignPtr((char*)buf1 + 200 * sizeof(int), 64);
//...
free(buf);

This pull request also proposes refactoring of StereoBM algorithm using introduced class. Note: buffers aligning to 64 bytes has been disabled during refactoring.

TODO list:

• Test
• Documentation
• Use in real algorithm

buildworker:Custom=linux-1
build_image:Custom=centos:7