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• ARM compiler update

  15 janvier 2010, par Mans — ARM, Compilers

  Since my last shootout, all the tested vendors have updated their compilers. Here is a quick update on each of them.

  Both the 4.3 and 4.4 branches of FSF GCC have had bugfix releases, bringing them to 4.3.4 and 4.4.2, respectively. Neither update contains anything particularly noteworthy.

  The CodeSourcery 2009q3 release sees an update to a GCC 4.4 base, a significant change from the 4.3 base used in 2009q1. The update is a mixed blessing. In fact, it is mostly a curse and hardly a blessing at all. On the bright side, the floating-point speed regressions in 2009q1 are gone, 2009q3 being a few per cent faster even than 2007q3. Unfortunately, this improvement is completely overshadowed by a major speed regression on integer code, a whopping 24% in one case. This ties in with the slowdown previously observed with FSF GCC 4.4 compared to 4.3.

  ARM RVCT 4.0 is now at Build 697. This update fixes some bugs and introduces others. Notably, it no longer builds FFmpeg correctly. The issue has been reported to ARM.

  Texas Instruments, finally, have made a formal release, v4.6.1, of their TMS470 compiler incorporating various fixes allowing it to build a moderately patched FFmpeg. The performance remains somewhere between GCC and RVCT on average.

  In light of the above, my recommendations remain unchanged :

  • For a free compiler, choose CodeSourcery 2009q1. It beats GCC 4.3.4 by 5-10% in most cases.
  • GNU purists are best served by GCC 4.3.4, which is up to 20% faster than 4.4.2 and rarely slower.
  • When price is not a concern, ARM RCVT is a good option, outperforming GCC by up to a factor 2.
  • In all cases, disable any auto-vectorisation features.

  Regardless of which compiler is chosen, I cannot overstress the importance of testing. All compilers are crawling with bugs, and even the most innocent-looking code change can trigger one of them. When using a compiler other than GCC, extra caution is advised considering a lot of code is developed using only GCC and may thus fall prey to bugs unique to said other compiler.

• Perspective transformations

  9 juin 2010, par Mikko Koppanen — Imagick, PHP stuff

  Finally (after a long break) I managed to force myself to update the PHP documentation and this time it was distortImage code example. Things have been hectic lately but that does not quite explain the 6 months(?) break between this and the previous post. As a matter of a fact there is no excuse for such a long silence so I will try to update this blog a bit more often from now on.

  Back in the day I used to blog the examples and update the documentation if I remembered but I am trying to fix this bad habit. Most of the latest examples have been updated in to the manual. In the case of the two last examples I updated the documentation first and then blogged on the subject.

  I took some time to actually understand the perspective transformations properly using the excellent ImageMagick examples (mainly created by Anthony Thyssen) as a reference. The basic idea of perspective distortion seems simple : to distort the control points to new locations. Grabbing the syntax for Imagick was easy, an array of control point pairs in the form of :

  php

  < view plain text >

  1. array(source_x, source_y, dest_x, dest_y ... )

  The following example uses the built-in checkerboard pattern to demonstrate perspective distortion :

  php

  < view plain text >

  1. < ?php
  2. /* Create new object */
  3. $im = new Imagick() ;
  4.  
  5. /* Create new checkerboard pattern */
  6. $im->newPseudoImage(100, 100, "pattern:checkerboard") ;
  7.  
  8. /* Set the image format to png */
  9. $im->setImageFormat(’png’) ;
  10.  
  11. /* Fill background area with transparent */
  12. $im->setImageVirtualPixelMethod(Imagick: :VIRTUALPIXELMETHOD_TRANSPARENT) ;
  13.  
  14. /* Activate matte */
  15. $im->setImageMatte(true) ;
  16.  
  17. /* Control points for the distortion */
  18. $controlPoints = array( 10, 10,
  19.             10, 5,
  20.  
  21.             10, $im->getImageHeight() - 20,
  22.             10, $im->getImageHeight() - 5,
  23.  
  24.             $im->getImageWidth() - 10, 10,
  25.             $im->getImageWidth() - 10, 20,
  26.  
  27.             $im->getImageWidth() - 10, $im->getImageHeight() - 10,
  28.             $im->getImageWidth() - 10, $im->getImageHeight() - 30) ;
  29.  
  30. /* Perform the distortion */ 
  31. $im->distortImage(Imagick: :DISTORTION_PERSPECTIVE, $controlPoints, true) ;
  32.  
  33. /* Ouput the image */ 
  34. header("Content-Type : image/png") ;
  35. echo $im ;
  36.  ?>

  Here is the source image :
  

  And the result :
  

• Revision 30164 : Code mort bis

  24 juillet 2009, par kent1@… — Log

  Code mort bis