[R] aligned memory allocation in C

[Jeffrey Horner]

Christophe Dutang1 wrote:
> Hi,
> 
> I'm currently R porting SF Mersenne Twister algorithm of Matsumoto and 
> Saito. To get the full power of their code, I want to use their fonction 
> fill_array32 which need aligned memory. That is to say I need to use the 
> C function memalign on windows, posix_memalign on linux and classic 
> malloc on Mac OS. In 'writing R extenstion', they recommand to use 
> R_alloc function to allocate memory in C.
> 
> Does R_alloc return a pointer to aligned memory?
> if not how can I do this?
> probably no, because R crashes when I succesively R_alloc and 
> fill_array32 (cf below) on my macbook with R 2.7.1.

You can still do this. Just take the address returned from R_alloc and 
test for alignment. If it's not, then just use an aligned address beyond 
the one returned.

(But then the question is, which direction beyond the one returned? How 
does one test for that?)

Jeff

> Thanks in advance
> 
> Kind regards
> 
> Christophe
> 
> 
> PS : 
> http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/SFMT/howto-compile.html provides 
> an example of memalign.
> 
> PPS : mac os report
> 
> Thread 0 Crashed:
> 0   libSystem.B.dylib                 0x9341bb9e __kill + 10
> 1   libSystem.B.dylib                 0x93492ec2 raise + 26
> 2   libSystem.B.dylib                 0x934a247f abort + 73
> 3   randtoolbox.so                    0x15e65f1d 0x15e5d000 + 36637
> 4   randtoolbox.so                    0x15e614ef fill_array32 + 4038
> 5   randtoolbox.so                    0x15e6513d SFmersennetwister + 335
> 6   randtoolbox.so                    0x15e652c6 doSFMersenneTwister + 255
> 7   libR.dylib                        0x00367a52 do_dotcall + 1394
> 8   libR.dylib                        0x0038b5a2 Rf_eval + 1754
> 9   libR.dylib                        0x0038f9a2 do_set + 592
> 10  libR.dylib                        0x0038b366 Rf_eval + 1182
> 11  libR.dylib                        0x0038b366 Rf_eval + 1182
> 12  libR.dylib                        0x0038c140 do_begin + 58
> 13  libR.dylib                        0x0038b366 Rf_eval + 1182
> 14  libR.dylib                        0x0038b366 Rf_eval + 1182
> 15  libR.dylib                        0x0038c140 do_begin + 58
> 16  libR.dylib                        0x0038b366 Rf_eval + 1182
> 17  libR.dylib                        0x0038d9a6 Rf_applyClosure + 663
> 18  libR.dylib                        0x0038b25d Rf_eval + 917
> 19  org.R-project.R                   0x000189c3 run_REngineRmainloop + 
> 569 (Rinit.m:442)
> 20  org.R-project.R                   0x0001142a -[REngine runREPL] + 
> 260 (REngine.m:181)
> 21  org.R-project.R                   0x00002e91 main + 795 (main.m:126)
> 22  org.R-project.R                   0x00002b5a _start + 216
> 23  org.R-project.R                   0x00002a81 start + 41
> 
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-- 
http://biostat.mc.vanderbilt.edu/JeffreyHorner