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Re: Converting Doubles to Strings [message #46149 is a reply to message #46148]

Mon, 07 November 2005 14:17

biophys
Messages: 68
Registered: July 2004

Member

Hi, David

I think I've got a more decent solution by assuming that double
precision numbers have exactly 14 significant digits and throw away
zeros at the end. In IDL help, it says that double type has
appoximately 14 digits of significance. So I am sure my solution will
fail somewhere. However, so far it works pretty nice. Please let me
know if any bugs should be fixed or any improvement should be made. A
few examples here,

IDL> print,dbl2str(-22.12)
-22.12E
IDL> print,dbl2str(-22.12d)
-22.12D
IDL> print,dbl2str(-22.1234567890)
-22.12346E
IDL> print,dbl2str(-22.1234567890d)
-22.123456789D
IDL> print,dbl2str(!dpi*1e20)
3.1415927165501E+20
IDL> print,dbl2str(!dpi*1d20)
3.1415926535897D+20

here's the code,

;converting float/double type numer into its original inputform
function dbl2str, a

tp=size(a,/type)
if tp ne 4 and tp ne 5 then begin
a=double(a)
tp=5
endif
tps=tp eq 4?'E':'D'

rawstr=strtrim(string(a,format='(g)'),2);full width G format
sign=strmid(rawstr,0,1) eq '-'?'-':'';extract sign
rawstr=sign eq ''?rawstr:strmid(rawstr,1);throw away sign
epos=strpos(rawstr,'e')
indx=epos gt -1?strmid(rawstr,epos+1):'';extract exponent index
rawstr=indx eq ''?rawstr:strmid(rawstr,0,epos);throw away exponent part
dpos=strpos(rawstr,'.');extract decimal point position

;rounding process(assume 14 significant digits)
outstr=strarr(15)
for i=0,14 do outstr[i]=strmid(rawstr,i,1)
aux=fix(strmid(rawstr,16,1)) ge 5?1:0
for i=14, 0, -1 do begin
if i ne dpos then begin
sumstr=strtrim(string(aux+fix(outstr[i])),2)
sumlen=strlen(sumstr)
outstr[i]=sumstr[sumlen-1]
aux=sumlen eq 1?0:1
endif
endfor

;throw away '0's at the end
ii=14
while outstr[ii] eq '0' do begin
ii=ii-1
endwhile

;reconstruct the inputform
saux=aux ne 0?'1':''
outstr=sign+saux+strjoin(outstr[0:ii])+tps+indx

return,outstr

end

cheers,
bp

David Fanning wrote:
> Folks,
>
> I've run into an interesting problem. I have a double precision
> number that I wish to convert to a string (so I can put it into
> a text widget, for example). I don't know ahead of time how many
> significant digits will be in this number. The number could
> look like this 45.6, or this 123456789.123456789, or this
> -22.1234567890. If it looks like the latter number, I am
> having a very hard time converting it to a string. For example,
> this doesn't work:
>
> IDL> v = String(-22.1234567890, Format='(D0)')
> IDL> Print, v
> -22.123457
>
> Is this a bug in IDL? Or am I overlooking something?
>
> Cheers,
>
> David
> --
> David Fanning, Ph.D.,
> Fanning Software Consulting, Inc.
> Coyote's Guide to IDL Programming: http://www.dfanning.com/

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[Message index]

		Re: Converting Doubles to Strings By: biophys on Mon, 07 November 2005 14:39
		Re: Converting Doubles to Strings By: biophys on Mon, 07 November 2005 14:17
		Re: Converting Doubles to Strings By: R.Bauer on Mon, 07 November 2005 11:53
		Re: Converting Doubles to Strings By: biophys on Sat, 05 November 2005 19:20
		Re: Converting Doubles to Strings By: biophys on Sat, 05 November 2005 17:01
		Re: Converting Doubles to Strings By: Craig Markwardt on Sat, 05 November 2005 07:31
		Re: Converting Doubles to Strings By: biophys on Sat, 05 November 2005 02:40
		Re: Converting Doubles to Strings By: Andrew Cool on Sat, 05 November 2005 01:46
		Re: Converting Doubles to Strings By: R.Bauer on Mon, 07 November 2005 22:42

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