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Re: float function unexpectedly slow [message #88232 is a reply to message #88029]

Mon, 31 March 2014 16:48

Heinz Stege
Messages: 189
Registered: January 2003

Senior Member

Hi all,

I know, I'm a little late with this message. When I read Tim's
posting, I had the idea to write my own system routine for converting
a string to float. And this idea I didn't get out of my mind. So here
is the story.

I'm not an expert in C. To tell the truth, I'm just a beginner. There
may be things in my C-code, which are not good. (Comments, which help
me learning, are welcome.) I'll place the code at the bottom of this
posting.

First let me give the results. str_to_double(), this is the new system
routine, makes about 50% more conversions per time than IDL's
double().

The following commands
str='363.491'
t0=systime(1) &for i=0,9999999 do x=double(str) &print,systime(1)-t0
take 5.90 s. The same with x=str_to_double(str) instead of
x=double(str) takes 3.81 s. I ran the commands several times in a
changing order.

I think, Chris is absolutely right with his recommendation to
eliminate any loops in the IDL program. So I did another test with an
array of strings:
str=strtrim(randomu(seed,1000000)*1000.,2)
t0=systime(1) &for i=0,9 do x=double(str) &print,systime(1)-t0
This takes 5.35 s for double() and 3.60 s for str_to_double. This is
very similar to the result with the scalar string.

Interesting, that in this test the loop does not cost much CPU time.
The conversion of 1 million scalar strings do not need much more time
than one array with 1 milionen elements. However str_to_double() is
significantly faster than double().

The tests are done with version { x86 Win32 Windows Microsoft Windows
8.0.1 Oct 5 2010 32 64}.

Cheers, Heinz

Here ist the C code:

static IDL_VPTR str_to_double(int argc,IDL_VPTR *argv)
{
IDL_VPTR result;

if (argv[0]->type != IDL_TYP_STRING) {

IDL_MessageFromBlock(msg_block,M_MSR_NO_STRING_TYPE,IDL_MSG_ LONGJMP,argv[0]- >type);
}

if (argv[0]->flags & IDL_V_ARR) {
IDL_STRING *str;
double *vector;
IDL_MEMINT i;

str=(IDL_STRING *) argv[0]->value.arr->data;
vector=(double *) IDL_MakeTempArray(IDL_TYP_DOUBLE,
argv[0]->value.arr->n_dim,

argv[0]->value.arr->dim,IDL_ARR_INI_NOP,&result);
for (i=0; i<argv[0]->value.arr->n_elts; i++) {
vector[i]=str[i].slen? atof(str[i].s) : 0.;
}
}
else {
double value;

value=argv[0]->value.str.slen? atof(argv[0]->value.str.s) : 0.;
result=IDL_GettmpDouble(value);
}

return result;
}

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[Message index]

		float function unexpectedly slow By: timothyja123 on Wed, 12 March 2014 16:56
		Re: float function unexpectedly slow By: Craig Markwardt on Wed, 12 March 2014 17:25
		Re: float function unexpectedly slow By: Phillip Bitzer on Wed, 12 March 2014 17:29
		Re: float function unexpectedly slow By: timothyja123 on Wed, 12 March 2014 17:31
		Re: float function unexpectedly slow By: Craig Markwardt on Wed, 12 March 2014 17:45
		Re: float function unexpectedly slow By: chris_torrence@NOSPAM on Wed, 12 March 2014 20:50
		Re: float function unexpectedly slow By: Heinz Stege on Mon, 31 March 2014 16:48
		Re: float function unexpectedly slow By: timothyja123 on Wed, 12 March 2014 17:38

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