On Fri, 29 May 2015 15:24:42 +0300 Siarhei Siamashka <siarhei.siamas...@gmail.com> wrote:
> On Fri, 29 May 2015 13:08:49 +0300 > Pekka Paalanen <ppaala...@gmail.com> wrote: > > > On Thu, 28 May 2015 16:08:55 -0300 > > Fernando Seiti Furusato <ferse...@linux.vnet.ibm.com> wrote: > > > > > Hi Ben. > > > > > > On 05/28/2015 01:57 PM, Fernando Seiti Furusato wrote: > > > > Hello Ben. > > > > > > > > On 05/27/2015 09:40 AM, Ben Avison wrote: > > > >> On Tue, 26 May 2015 19:16:32 +0100, I wrote: > > > >> > > > >>> + color.alpha = prng_rand_n (UINT16_MAX); > > > >>> + color.red = prng_rand_n (UINT16_MAX); > > > >>> + color.green = prng_rand_n (UINT16_MAX); > > > >>> + color.blue = prng_rand_n (UINT16_MAX); > > > >> > > > >> Oops, those should have been UINT16_MAX + 1; the argument is used as a > > > >> modulo not as a bitmask. The corresponding checksum is then 0xC30FD380 > > > >> for me on ARM and x86 (both little-endian of course). > > > > > > > > I am sorry, I did not receive the original message you sent. > > > > Luckily I looked in the archive and saw it in the same thread. > > > > I will be looking into this, thanks for contacting me. > > > > > > I have just tested that patch with these last adjustments you sent > > > afterwards. > > > The solid-test passed on all of the 3: ppc64le, ppc64 and powerpc. > > > > Ok, cool. > > > > But, I'm still a little confused as to why the patch makes a > > difference. Sure, it changes the byte ordering when assigning random > > values, but the values are still equally random, right? > > Yes, the process of generating pseudo-random numbers is equally > random either way. Just the results and the CRC32 end up different > because random numbers land in different slots and are used for > different things. It is somewhat similar to using a different seed. > > For example, if you are generating an a8r8g8b8 pixel and want it > to be the same on big and little endian systems, it needs to be > generated as a 32-bit pseudo-random number and not as an array > of 8-bit values. This way red pixels remain red, opaque pixels > remain opaque, etc. > > Either the process of generating random images needs to take care > of the endian differences, or we can have separate CRC32 checksums > for big and little endian systems. Currently pixman prefers the > former approach. D'oh! Thank you. :-) Ben, could you prep a final patch from this, complete with Fernando's Tested-by and the list of archs where tested? Thanks, pq _______________________________________________ Pixman mailing list Pixman@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/pixman
