Difference between revisions of "User:Pedro Oval/Mono code memory usage"

From Second Life Wiki
Jump to navigation Jump to search
(More constructs)
(More surprising results)
Line 1: Line 1:
Here are some memory usage results I've obtained with Mono, for common language constructs. They were obtained by replicating each line to test 512 times and looking at llGetFreeMemory right at the beginning of the script.
Here are some memory usage results I've obtained with Mono, for common language constructs. They were obtained by replicating each line to test 512 times and looking at [[llGetFreeMemory]] right at the beginning of the script.


Results for local integer variables x, y, and local float variables f, g:
Results for local integer variables x, y, and local float variables f, g:
Line 29: Line 29:
| -x    || 3  ||
| -x    || 3  ||
|-
|-
| ~x    || 3  ||
| ~x    || 3  || Bitwise, equivalent to -x-1 which allows it to be used for some hacks
|-
|-
| !x    || 5  ||
| !x    || 5  || Logical
|-
|-
| --x    || 6  || Pre-decrement (same bytes as x=~-x)
| --x    || 6  || Pre-decrement (same bytes as x=~-x)
Line 44: Line 44:
|-
|-
| x==y  || 5  || Comparison
| x==y  || 5  || Comparison
|-
| x=y=z  || 6  || (for local integer z) Chained assignment
|-
|-
| f=x    || 5  || Implicit conversion from integer to float
| f=x    || 5  || Implicit conversion from integer to float
Line 139: Line 141:
| for(;x;); || 37 || For loops seem to be plainly rewritten as while loops
| for(;x;); || 37 || For loops seem to be plainly rewritten as while loops
|-
|-
| @label; if(x) jump label; || 37  || Equivalent to do loops, saves 4 bytes.
| @label; if(x) jump label; || 37  || Equivalent to a do...while loop, saves 4 bytes.
|}
|}

Revision as of 14:50, 8 February 2013

Here are some memory usage results I've obtained with Mono, for common language constructs. They were obtained by replicating each line to test 512 times and looking at llGetFreeMemory right at the beginning of the script.

Results for local integer variables x, y, and local float variables f, g:

Construct Bytes used Comments
; 0
{} 0
return 1 Tested in event and without arguments
x 2
(x) 2
(integer)x 2
(float)x 3
f 2
(float)f 2
(integer)f 7
-x 3
~x 3 Bitwise, equivalent to -x-1 which allows it to be used for some hacks
!x 5 Logical
--x 6 Pre-decrement (same bytes as x=~-x)
++x 6 Pre-increment (same bytes as x=-~x)
x-- 8 Post-decrement
x++ 8 Post-increment
x=y 4 Assignment
x==y 5 Comparison
x=y=z 6 (for local integer z) Chained assignment
f=x 5 Implicit conversion from integer to float
f=(float)x 5 Explicit conversion from integer to float
x!=y 8 Same bytes as !(x==y)
x*y 4
x/y 8
x%y 8 Modulo
x+y 4
x-y 8 !?!?
x+-y 5 Saves 3 bytes vs. a subtraction!
x*y 4
x/y 8
x&y 4 Bitwise
x&&y 13 Logical
x|y 4 Bitwise
x||y 10 Logical
x^y 4 Bitwise
x<<y 8 Bitwise shift left (can be simulated with mult in most cases)
x>>y 8 Bitwise shift right
x<y 5
x>y 5
x<=y 8 Same bytes as !(x>y)
x>=y 8 Same bytes as !(x<y)
x+=y 6 Same bytes as x=x+y
x-=y 10 Same bytes as x=x-y
x+=-y 7 Saves 3 bytes vs x-=y
x*=y 6 Same as x=x*y
x/=y 10 Same as x=x/y
x%=y 10 Same as x=x%y
if(x); 6
if(x); else; 11
0 6
x^x 4 It gives always 0, saving 2 bytes. (Thanks to User:Omei Qunhua for the discovery)
1 6
-1 7 Sign takes code memory.
0xffffffff 6 Equivalent to -1.
x|~x 5 Equivalent to -1. Saves 1 byte vs 0xffffffff, 2 bytes vs -1.
x+1 8
-~x 4 Same as x+1, saves 4 bytes
x-1 12 What's wrong with subtraction?
x+-1 9 Same as x-1, saves 3 bytes
~-x 4 Same as x-1, saves 8 bytes
x*y+y-1 16 This kind of construct is sometimes used to access last element of strided lists
(x+1)*y-1 20 Equivalent to the above, just worse
~(~x*y) 6 Equivalent to the above, saves 10 bytes
while(x); 37
do ; while(x); 41 Unexpected but true
for(;x;); 37 For loops seem to be plainly rewritten as while loops
@label; if(x) jump label; 37 Equivalent to a do...while loop, saves 4 bytes.