Multidimensional array access performance in C#

Question

I have seen that C# "is optimized" for accessing 1D array (does not call a function to access element), but for multidim-arrays function GetValue is called each time. Why not instead of calling this function each time "normal" access (pointers shifting + checking) is not implemented or at least this function is not flattened ?

I can not find the logical reason. (performance for multidim-arrays are not great)

Feng Yuan · Accepted Answer · 2012-07-16 04:12:22Z

1

I tried it out, it's about 14 instructions per element access, due to bounds check and multiplication by dimension size.

If perf is important, use 1D array of pinning to pointer.

answered Jul 16, 2012 at 4:12

Feng Yuan

7075 silver badges4 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

dajuric · Accepted Answer · 2012-07-24 17:16:46Z

1

I didn't uncheck "Supress JIT optimization..." therefore function call GetValue wasn't inlined.

Optimized code:

b = a[3, 5];
00000026  mov         eax,3 
0000002b  lea         edx,[eax+2] 
0000002e  sub         eax,dword ptr [ecx+10h] 
00000031  cmp         eax,dword ptr [ecx+8] 
00000034  jae         0000010B 
0000003a  sub         edx,dword ptr [ecx+14h] 
0000003d  cmp         edx,dword ptr [ecx+0Ch] 
00000040  jae         0000010B 
00000046  imul        eax,dword ptr [ecx+0Ch] 
0000004a  add         eax,edx 
0000004c  mov         edi,dword ptr [ecx+eax*4+18h]

answered Jul 24, 2012 at 17:16

dajuric

2,5473 gold badges21 silver badges45 bronze badges

Collectives™ on Stack Overflow

Multidimensional array access performance in C#

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related