1. and...and...and
- Posted by Robert Craig <rds at CLASSIC.MSN.COM> Sep 15, 1997
- 2758 views
Einar Mogen writes: > Then, I discovered something about speed last night. This could be old news for > all you, but of these two "if's": > if ... and ... and ... and ... then > <...> > end if > if ... then > if ... then > if ... then > if ... then > <...> > end if > end if > end if > end if > -the last one is the fastest. Shouldn't Euphoria just skip the rest of an "if > ... and" line if the first part checks false? It seems to me that all parts of > an "if ... and ... and" line is checked each time, which did result in a > slowdown in my game. You are correct. Euphoria does not do "short-circuit" evaluation of and/or/not conditions. I have this on my list of desirable features, but it might not happen for a while, if at all, because: 1. It's hard to retrofit this in to ex.exe. 2. It would break some people's existing code (only a tiny percentage I would guess) in the case where there are side effects from evaluation (e.g. function call sets a global variable) 3. Euphoria's conditional expressions can involve sequences, as well as atoms. e.g. if A and B then ..., where A is 1 and B is {0,1,2} is supposed to evaluate to {0,1,1} which is supposed to cause an error when used in an if statement. We'd have to accept A and B as being "true" without any error message. > Do the rest of you know of other "trivial things" which could have a > major impact on speed? In Euphoria there are a surprising number (even to me) of trivial things that can affect performance. This is generally due to the fact that Euphoria does not map directly to machine code the way C does. The Euphoria interpreter is doing "invisible" things, such as storage allocation, in order to give you a simple, safe, flexible world to program in. Fortunately, in Euphoria you have the ability to profile your code using: with profile or with profile_time If you care about performance you really should profile your code at least once. Do not assume that you "know" which sections of code are consuming most of the time. You will *often* be surprised. You can also time small sections of code using: atom t t = time() for i = 1 to 1000000 do -- your code goes here end for ?(time()-t)/1000000 Regards, Rob Craig Rapid Deployment Software
2. Re: and...and...and
- Posted by Ralf Nieuwenhuijsen <nieuwen at XS4ALL.NL> Jan 01, 1970
- 2757 views
Robert Craig wrote: > > -the last one is the fastest. Shouldn't Euphoria just skip the rest > of an > "if > > ... and" line if the first part checks false? It seems to me that > all parts > of > > an "if ... and ... and" line is checked each time, which did result > in a > > slowdown in my game. > > You are correct. Euphoria does not do "short-circuit" evaluation of > and/or/not > conditions. > I have this on my list of desirable features, but it might not happen > for a > while, > if at all, because: > > 1. It's hard to retrofit this in to ex.exe. Can't you put it in the precompiler as different if's > 2. It would break some people's existing code (only a tiny > percentage I > would guess) > in the case where there are side effects from evaluation (e.g. > function > call sets a global variable) The precompiler makes a first if with only those evulations that have a side effect. (That call another function or routine). After that it can compile the rest of the evalutions on different (sub)-ifs > 3. Euphoria's conditional expressions can involve sequences, as > well as > atoms. e.g. > if A and B then ..., where A is 1 and B is {0,1,2} is supposed > to > evaluate to {0,1,1} > which is supposed to cause an error when used in an if > statement. We'd > have to > accept A and B as being "true" without any error message. Have the objects also in the first if. > > Do the rest of you know of other "trivial things" which could have a > > > major impact on speed? > > In Euphoria there are a surprising number (even to me) > of trivial things that can affect performance. This is generally due > to the > fact that Euphoria does not map directly to machine code the way C > does. > The Euphoria interpreter is doing "invisible" things, such as storage > allocation, > in order to give you a simple, safe, flexible world to program in. I'll give you two examples that will show a weird speed difference... -- Example 1 function my_func (sequence r) sequence s s = r[1][2][3][4] if s[1] = 1 then elsif s[2] = 2 then elsif s[3] = 3 then elsif s[4] = 4 then elsif s[5] = 5 then elsif s[6] = 6 then end if my_procedure (s+4+s) return s+ (s*2) end function -- Example 2 function my_func (sequence r) if r[1][2][3][4][1] = 1 then elsif r[1][2][3][4][2] = 2 then elsif r[1][2][3][4][3] = 3 then elsif r[1][2][3][4][4] = 4 then elsif r[1][2][3][4][5] = 5 then elsif r[1][2][3][4][6] = 6 then end if my_procedure (r[1][2][3][4]+4+r[1][2][3][4]) return r[1][2][3][4]+ (r[1][2][3][4]*2) end function -- End of examples The first code looks nicer, but declares a sequence and copy r[1][2][3][4] to it. and that code is still faster (on my machine: p60, 24 mb, win95) I think it is because every time you use r[1][2][3][4], it looks up r[1] then r[1][2] then r[1][2][3] then r[1][2][3][4]. (It will be passed forwared 3 times) However the other code doens't actually copy it. It only copies the link/ the pointer to the sequence of r[1][2][3][4]. And when we change a value in it, Then it will start copying the whole sequence. (But we don't) Ralf Nieuwenhuijsen nieuwen at xs4all.nl