User:Pedro Oval/Mono code memory usage

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.

Includes tips on memory reduction, with the corresponding savings. In some cases, "same bytes as (something)" is indicated, which means that the constructs are equivalent but offer no savings.

Notation below is that x, y are local integer variables; f, g are local float variables, v is a local vector variable, a is a list

Construct	Bytes used	Comments
;	0	Empty statement, e.g. ;;;;;; takes same mem as ;
{}	0	Empty statement e.g. {{{{{}}}}} takes same mem as {}
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
v	2
v.z	8	Vector component
-x	3
~x	3	Bitwise, equivalent to -x-1 which allows it to be used for some hacks. Not applicable to floats though.
!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. Same bytes as -~(x=~-x)
x++	8	Post-increment. Same bytes as ~-(x=-~x)
x=y	4	Assignment
x==y	5	Comparison
x=y=z	6	(for local integer z) Chained assignment
f=x	5	Implicit cast from integer to float
f=(float)x	5	Explicit cast from integer to float
x!=y	8	Same bytes as !(x==y). Can sometimes be replaced by x^y, saving 4 bytes.
x+y	4
x-y	8	!?!?
x+-y	5	Saves 3 bytes vs. a subtraction!
x*y	4	Can sometimes be used instead of x << bits, saving 4 bytes.
x/y	8
x%y	8	Modulo
x&y	4	Bitwise
x&&y	13	Logical. Same bytes as !(!x|!y)
x|y	4	Bitwise
x||y	10	Logical. Same bytes as !!(x|y)
x^y	4	Bitwise. Can sometimes be used instead of x!=y (if careful), saving 4 bytes.
x<<y	8	Bitwise shift left. Can be replaced with a multiplication in some cases, saving 4 bytes.
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.
ALL_SIDES	6	Value is -1. Constants with negative values don't take memory for the sign.
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.
0.0	10	Float constants use a lot of memory.
f=0.0	12
f=0	9	In general, using integer constants with implicit conversion to float instead of float constants saves 3 bytes every time. Another example follows.
<0.0, 0.0, 0.0>	33	Same as ZERO_VECTOR
ZERO_VECTOR	33
<0, 0, 0>	24	Saves 3 bytes per constant
<-1.0, -1.0, 0.0>	35	(because of the signs). Equivalent to TOUCH_INVALID_TEXCOORD.
TOUCH_INVALID_TEXCOORD	33
<-1, -1, 0>	26	(because of the signs)
<0xffffffff, 0xffffffff, 0>	24	(no signs but ugly)
v+v	8	Vector addition (with the vectors as local variables)
v-v	8	Vector subtraction
v*v	8	Vector dot product
v%v	8	Vector cross product
[]	6	Empty list
a=[]	8	Assignment of empty list
a+[x]	23	Append an element to a list, with brackets
a+x	8	Append an element to a list, without brackets
[x]+a	23	Prepend an element to a list, with brackets
x+a	13	Prepend an element to a list, without brackets
[x]	17	List with an integer
[]+x	12	Empty list plus an integer element appended, saves 5 bytes with respect to [x]
(list)x	12	Same bytes as []+x
[x,y]	28	List with two integers (the type of variable doesn't seem to affect the result)
[]+x+y	18	Empty list with two integer elements appended, saves 10 bytes with respect to [x,y] (the type of variable doesn't seem to affect the result)
(string)a	7	Typecasting a list to a string

See also

• User:Omei Qunhua
• User talk:Omei Qunhua