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freds72
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Working on my game, I often find myself wondering how much cpu such or such construct uses.
I do my benchmarks using stat(1).
Issue is, my measures are all over the place according to the number of samples :[

Ex: Let's bench band vs. % and shr vs / @ 100 calcs/update

Good, % is almost free, / is slightly better than shr
Let's try 200:

Hu? shr is now better than /

Push it to 300:

Back to "normal"

400:

WTF?

How come number of samples for a given run is turning results upside down?
Note: if I push number of iterator further, I tend to have stable results - but who's performing 5000% per update cycle?!?
On top of that, @zep, we should be provided with op cost of basic operations (similar to cpu specs).

Reference code:

 
function bench(name,n,fn)
    local t0=stat(1)
    for i=1,n do
        fn(i)
    end
    return {name,(stat(1)-t0)}
end
function stat2pct(s)
    return flr(1000*s)/10
end
function bench_draw(name1,stat1,name2,stat2,y)
    print(name1.." vs. "..name2,1,y,7)
    y+=6
    local total=stat1+stat2
    local pct1,pct2=stat1/total,stat2/total
    local c1,c2=8,11
    if(stat1<stat2) c1=11 c2=8
    local x=flr(128*pct1)
    rectfill(0,y,x+1,y+6,c1)
    x+=1
    print(stat2pct(stat1),x/2,y+1,0)
    local x2=128*pct2
    local msgx2=x+x2/2
    if(x2<1) then
        x=127 x2=127 msgx2=120
    end
    rectfill(x,y,x+x2,y+6,c2)
    print(stat2pct(stat2),msgx2,y+1,0)
    y+=8    
    return y
end

local res={}
local n=100
function _update60()
    if(btnp(0)) n-=100
    if(btnp(1)) n+=100
    n=max(n,100)

    res={}
    add(res,bench("band",n,function()
        j=band(546,127)
    end))
    add(res,bench("%",n,function()
        j=546%128
    end))

    add(res,bench("shr",n,function()
        j=90/8
    end))
    add(res,bench("/",n,function()
        j=shr(90,3)
    end))
end

function _draw()
    cls(0)

    rectfill(0,0,127,6,1)
    print(n.." iterations - \139\145 to change",1,1,7)

    local y=9
    for i=1,#res,2 do
        y=bench_draw(res[i][1],res[i][2],res[i+1][1],res[i+1][2],y)
    end
end
P#43888 2017-09-03 05:12 ( Edited 2017-09-09 13:27)