How to refresh cached image ONCE

[C. (http://symcbean.blogspot.com/)]

Hi all,

I have an application which generates image graphs. These cache nicely
at the client, however if the user submits more data, I'd like to
force a reload of the image from the server.

I had a google, but all I could find were suggestions to use a varying
query in the URL. This is not a solution to my problem because if I
change the page to do that then ALL the graphs will be reloaded every
time.

I tried

document.getElementById("imgs_id_tag").src.reload( ):

and

document.getElementById("imgs_id_tag").reload():

But just got errors.

(If I open JUST the image URL in a browser, I get the cached version,
if I then click on refresh, it goes back to the server to get a new
copy - which is what I want).

Any suggestions?

TIA

C.

[webbugtrack]

you can try this...

var elem = document.getElementById("imgs_id_tag");
var oldSrc = elem.src;
elem.src = oldSrc + '?rnd=' + new Date().getTime();

This basically says "set the src to the exact same thing, with an
aditional 'random' parameter (current date/time as a number)"

HTH

[Jorge]

On Jul 18, 7:06*pm, "C. (http://symcbean.blogspot.com/)"
<[e-mail]:

Hi all,

I have an application which generates image graphs. These cache nicely
at the client, however if the user submits more data, I'd like to
force a reload of the image from the server.

I had a google, but all I could find were suggestions to use a varying
query in the URL. This is not a solution to my problem because if I
change the page to do that then ALL the graphs will be reloaded every
time.

I tried

document.getElementById("imgs_id_tag").src.reload( ):

and

document.getElementById("imgs_id_tag").reload():

But just got errors.

(If I open JUST the image URL in a browser, I get the cached version,
if I then click on refresh, it goes back to the server to get a new
copy - which is what I want).

Any suggestions?

image.src+= "?"+Math.random();

--Jorge

[Stanislav]

On 18 Jul., 19:06, "C. (http://symcbean.blogspot.com/)"
<[e-mail]:

Hi all,

I have an application which generates image graphs. These cache nicely
at the client, however if the user submits more data, I'd like to
force a reload of the image from the server.

I had a google, but all I could find were suggestions to use a varying
query in the URL. This is not a solution to my problem because if I
change the page to do that then ALL the graphs will be reloaded every
time.

I tried

document.getElementById("imgs_id_tag").src.reload( ):

and

document.getElementById("imgs_id_tag").reload():

But just got errors.

(If I open JUST the image URL in a browser, I get the cached version,
if I then click on refresh, it goes back to the server to get a new
copy - which is what I want).

Any suggestions?

TIA

C.

Hi,

You should send right http headers to the client.

More about this: http://developer.yahoo.com/performance/rules.html
under Add an Expires or a Cache-Control Header

;)

Best,
Stanislav

[Thomas 'PointedEars' Lahn]

we*********@gmail.com wrote:

you can try this...

var elem = document.getElementById("imgs_id_tag");

The `images' collection should be used instead:

var elem = document.images["imgs_id_tag"];

var oldSrc = elem.src;

What for?

elem.src = oldSrc + '?rnd=' + new Date().getTime();

This basically says "set the src to the exact same thing, with an
aditional 'random' parameter (current date/time as a number)"

Because it is not considered the same thing by the user agent, it will fill
up its cache (if enabled), leaving less space for other, maybe more
important data.

Also, a random value alone is not sufficient; it must be a value that is
unique over a longer period of time, like the timestamp that you suggested.

Cache-controlling HTTP headers are the correct approach instead.

Please do a little research before you post something here.

<http://jibbering.com/faq/>
PointedEars
--
Use any version of Microsoft Frontpage to create your site.
(This won't prevent people from viewing your source, but no one
will want to steal it.)
-- from <http://www.vortex-webdesign.com/help/hidesource.htm>

[Jorge]

On Jul 18, 7:50*pm, Thomas 'PointedEars' Lahn <[e-mail]>
wrote:

>
Also, a random value alone is not sufficient;

Yes it is, Thomas, remember that the OP said that he wanted to reload
the image *once*.

it must be a value that is
unique over a longer period of time, like the timestamp that you suggested.

The probability of obtaining the same ramdom number twice in a row is
about 1/(2^(8*8)) === 1/18446744073709551615
And keeps being almost null even after tens or hundreds of
extractions.

If you want to experiment how long that period of time can be, try
this : it will hang your browser until Math.random() repeats a certain
value :-)

javascript:n= 0, a= Math.random();while(a !== Math.random()){n+
+};alert(n);

--Jorge.

[Jorge]

On Jul 18, 7:50*pm, Thomas 'PointedEars' Lahn <[e-mail]>
wrote:

>
Cache-controlling HTTP headers are the correct approach instead.

Right. Cache-control headers ought to be explicitly setup just for
these images. Agreed.

But the OP was looking for a client-side solution, and that's not.

And the proposed solution will get the image reloaded regardless of
the (cache control) headers sent/received.

Please do a little research before you post something here.

Grrr.

--Jorge.

[Jorge]

On Jul 18, 9:16*pm, Jorge <[e-mail]:

>
javascript:n= 0, a= Math.random();while(a !== Math.random()){n+
+};alert(n);

On my Mac it took 2,147,483,645 iterations to get "a" repeated.

--Jorge.

[Thomas 'PointedEars' Lahn]

Jorge wrote:

Thomas 'PointedEars' Lahn wrote:

>Cache-controlling HTTP headers are the correct approach instead.

Right. Cache-control headers ought to be explicitly setup just for
these images. Agreed.

But the OP was looking for a client-side solution, and that's not.

| I have an application which generates image graphs. These cache nicely
| at the client, however if the user submits more data, I'd like to
| force a reload of the image from the server.

Not a single word about a client-side only solution.

And the proposed solution will get the image reloaded regardless of
the (cache control) headers sent/received.

The server must send an appropriate expiry value and ETag in the headers,
and the client must refresh the images often enough. If the expiry date was
met, the ETag changed or the resource was not in the cache in the first
place, it would be downloaded (again) from the server; if not, the cache
would be used. ISTM anything else would require a server-push communication
like Comet.

>Please do a little research before you post something here.

Grrr.

Now I have given you a reason for that.
PointedEars
--
realism: HTML 4.01 Strict
evangelism: XHTML 1.0 Strict
madness: XHTML 1.1 as application/xhtml+xml
-- Bjoern Hoehrmann

[Jorge]

On Jul 19, 3:48*am, Thomas 'PointedEars' Lahn <[e-mail]>
wrote:

Jorge wrote:

Thomas 'PointedEars' Lahn wrote:

Cache-controlling HTTP headers are the correct approach instead.

Right. Cache-control headers ought to be explicitly setup just for
these images. Agreed.

But the OP was looking for a client-side solution, and that's not.

| I have an application which generates image graphs. These cache nicely
| at the client, however if the user submits more data, I'd like to
| force a reload of the image from the server.

Not a single word about a client-side only solution.

Does this look like server-side scripting to you : (?)

"I tried document.getElementById("imgs_id_tag").src.reload( ): "
"and document.getElementById("imgs_id_tag").reload(): "

(...)
ISTM anything else would require a server-push communication
like Comet.

Duh !

--Jorge.

[Thomas 'PointedEars' Lahn]

Jorge wrote:

Thomas 'PointedEars' Lahn wrote:

>Jorge wrote:

>>Thomas 'PointedEars' Lahn wrote:
Cache-controlling HTTP headers are the correct approach instead.
Right. Cache-control headers ought to be explicitly setup just for
these images. Agreed.
But the OP was looking for a client-side solution, and that's not.

| I have an application which generates image graphs. These cache nicely
| at the client, however if the user submits more data, I'd like to
| force a reload of the image from the server.

Not a single word about a client-side only solution.

Does this look like server-side scripting to you : (?)

"I tried document.getElementById("imgs_id_tag").src.reload( ): "
"and document.getElementById("imgs_id_tag").reload(): "

I have noticed that before. So the OP had a problem with their client-side
script for refreshing the image. That does not mean in any way that the
solution must be client-side only.

>(...)
ISTM anything else would require a server-push communication
like Comet.

Duh !

Tough luck.
PointedEars
--
Use any version of Microsoft Frontpage to create your site.
(This won't prevent people from viewing your source, but no one
will want to steal it.)
-- from <http://www.vortex-webdesign.com/help/hidesource.htm>

[C. (http://symcbean.blogspot.com/)]

On Jul 19, 10:44*am, Thomas 'PointedEars' Lahn <[e-mail]>
wrote:

Jorge wrote:

Thomas 'PointedEars' Lahn wrote:

Jorge wrote:
Thomas 'PointedEars' Lahn wrote:
Cache-controlling HTTP headers are the correct approach instead.
Right. Cache-control headers ought to be explicitly setup just for
these images. Agreed.
But the OP was looking for a client-side solution, and that's not.
| I have an application which generates image graphs. These cache nicely
| at the client, however if the user submits more data, I'd like to
| force a reload of the image from the server.

Not a single word about a client-side only solution.

Does this look like server-side scripting to you : (?)

"I tried document.getElementById("imgs_id_tag").src.reload( ): "
"and document.getElementById("imgs_id_tag").reload(): "

I have noticed that before. *So the OP had a problem with their client-side
script for refreshing the image. *That does not mean in any way that the
solution must be client-side only.

(...)
ISTM anything else would require a server-push communication
like Comet.

Thanks guys - unfortunately it doesn't really solve my proble - I
guess I didn't make it clear enough.

I really want the image to be cached client side unless the data used
to create the image (server-side) changes. I can't really get every
client who has a cached copy to update their cache. Using a dirrent
URI each time by appending a random value just makes the browser think
it is a different image - undermining the caching which is working
fine in most cases:

had a google, but all I could find were suggestions to use a varying
query in the URL. This is not a solution to my problem because if I
change the page to do that then ALL the graphs will be reloaded every
time.

However, I think it may be possible to do for the client who just
uploaded the data - since, if they click the 'Refresh' button in the
browser it carries out an unconditional reload of the content. I'm
wanting to emulate this from Javascript.

C.

[Thomas 'PointedEars' Lahn]

C. (http://symcbean.blogspot.com/) wrote:

I really want the image to be cached client side unless the data used to
create the image (server-side) changes.

That is what cache-controlling headers are for: <http://mnot.net/cache-docs>

I can't really get every client who has a cached copy to update their
cache.

Why not?

Using a dirrent URI each time by appending a random value just makes the
browser think it is a different image - undermining the caching which is
working fine in most cases:

This is updating the cache in a sense, only that it is filled with mostly
useless information then. You hardly want that.

>had a google, but all I could find were suggestions to use a varying
query in the URL. This is not a solution to my problem because if I
change the page to do that then ALL the graphs will be reloaded every
time.

However, I think it may be possible to do for the client who just
uploaded the data - since, if they click the 'Refresh' button in the
browser it carries out an unconditional reload of the content. I'm
wanting to emulate this from Javascript.

Have you already tried executing

img.src = img.src;

or

var oldsrc = img.src;
img.src = "";
img.src = oldsrc;

in a repetitive setTimeout() while using cache-controlling headers?
PointedEars
--
Use any version of Microsoft Frontpage to create your site.
(This won't prevent people from viewing your source, but no one
will want to steal it.)
-- from <http://www.vortex-webdesign.com/help/hidesource.htm>

[Dr J R Stockton]

In comp.lang.javascript message <29d0c3f4-9a1e-4301-81b6-6dc5da5436b9@y3
8g2000hsy.googlegroups.com>, Fri, 18 Jul 2008 12:16:30, Jorge
<jo***@jorgechamorro.composted:

>On Jul 18, 7:50*pm, Thomas 'PointedEars' Lahn <[e-mail]>
wrote:

>>
Also, a random value alone is not sufficient;

Yes it is, Thomas, remember that the OP said that he wanted to reload
the image *once*.

>it must be a value that is
unique over a longer period of time, like the timestamp that you suggested.

The probability of obtaining the same ramdom number twice in a row is
about 1/(2^(8*8)) === 1/18446744073709551615
And keeps being almost null even after tens or hundreds of
extractions.

No, for two reasons. The generator is not necessarily 64-bit or even
53-bit. In my js-randm.htm, "MSIE 6 and 7 show 53 bits; Firefox 2.0.0.3
shows 52 bits; Opera 9.21 shows 31 bits; Safari 3.1 shows 31 bits."
And, as the generator is only pseudo-random, it should not repeat until
after a full cycle.

What does that page report (for various browsers?) on your Mac?

--
(c) John Stockton, nr London, UK. ?@merlyn.demon.co.uk Turnpike v6.05.
Web <URL:http://www.merlyn.demon.co.uk/- w. FAQish topics, links, acronyms
PAS EXE etc : <URL:http://www.merlyn.demon.co.uk/programs/- see 00index.htm
Dates - miscdate.htm moredate.htm js-dates.htm pas-time.htm critdate.htm etc.

[Dr J R Stockton]

In comp.lang.javascript message <48**************@PointedEars.de>, Fri,
18 Jul 2008 19:50:07, Thomas 'PointedEars' Lahn <Po*********@web.de>
posted:

>

>elem.src = oldSrc + '?rnd=' + new Date().getTime();

This basically says "set the src to the exact same thing, with an
aditional 'random' parameter (current date/time as a number)"

>Also, a random value alone is not sufficient; it must be a value that is
unique over a longer period of time, like the timestamp that you suggested.

In most browser instances, Math.random can be shown to give 53 bits of
pseudo-randomness, although the initial value's randomness depends on
the quality of the initialisation.

Machines connected to the Internet generally resynchronise from time to
time with an Internet or server clock. Nearly 50% of computers will
need to be set back in time, and in the case of those which cannot be
slowed or stopped but must jump back it will be necessary to repeat a
certain amount of internal-clock time. So new Date().getTime() may
give the same value after an interval as it did before. That will not
often happen, but ISTM likely to happen more often than the repeat of a
good RNG, let alone of a a PRNG which will cycle through all possible
values before repeating.
Recommending adjusting HTTP headers as opposed to adjusting the 'URL' is
not helpful to those whose servers do not allow header control.
Professional servers should allow it; those available to many of the
amateurs who read this group may very well not do so.

>Please do a little research before you post something here.

Please think before you post something here.

--
(c) John Stockton, nr London, UK. ?@merlyn.demon.co.uk Turnpike v6.05.
Web <URL:http://www.merlyn.demon.co.uk/- w. FAQish topics, links, acronyms
PAS EXE etc : <URL:http://www.merlyn.demon.co.uk/programs/- see 00index.htm
Dates - miscdate.htm moredate.htm js-dates.htm pas-time.htm critdate.htm etc.

[Jorge]

On Jul 19, 6:07*pm, Dr J R Stockton <[e-mail]:

>
No, for two reasons. *The generator is not necessarily 64-bit or even
53-bit. *In my js-randm.htm, "MSIE 6 and 7 show 53 bits; Firefox 2.0.0.3
shows 52 bits; Opera 9.21 shows 31 bits; Safari 3.1 shows 31 bits."
And, as the generator is only pseudo-random, it should not repeat until
after a full cycle.

Yes you're right. In fact Safari's PRNG always repeats at n=
2,147,483,645 (-2^31) (don't tell Thomas :-)

What does that page report (for various browsers?) on your Mac?

"Apparent resolution is at least 30 bits."

Thanks,
--Jorge.

[Jorge]

On Jul 19, 6:07*pm, Dr J R Stockton <[e-mail]:

>
What does that page report (for various browsers?) on your Mac?

On a Mac :

Webkit r34974: "Apparent resolution is at least 30 bits."
Safari 3.1.2: "Apparent resolution is at least 30 bits."

Opera 9.51: "Apparent resolution is at least 31 bits."

Navigator 9.0.0.3: "Apparent resolution is at least 52 bits."
Camino 1.6.1: "Apparent resolution is at least 52 bits."
FF 2.0.0.16: "Apparent resolution is at least 52 bits."
FF 3.1: "Apparent resolution is at least 52 bits."

IE 5.2: "Apparent resolution is at least 53 bits."

iCab 3.0.5 : "Apparent resolution is at least 58 bits."

--Jorge

[Jorge]

On Jul 19, 6:07 pm, Dr J R Stockton <[e-mail]:

What does that page report (for various browsers?) on your Mac?

On a Mac :
Webkit r34974: "Apparent resolution is at least 30 bits."
Safari 3.1.2: "Apparent resolution is at least 30 bits."

Opera 9.51: "Apparent resolution is at least 31 bits."

Navigator 9.0.0.3: "Apparent resolution is at least 52 bits."
Camino 1.6.1: "Apparent resolution is at least 52 bits."
FF 2.0.0.16: "Apparent resolution is at least 52 bits."
FF 3.1: "Apparent resolution is at least 52 bits."

IE 5.2.3: "Apparent resolution is at least 53 bits."

iCab 3.0.5: "Apparent resolution is at least 58 bits."

--Jorge

[Dr J R Stockton]

In comp.lang.javascript message <c9681dae-4958-410e-993b-86bb9eeddd00@l4
2g2000hsc.googlegroups.com>, Sat, 19 Jul 2008 12:37:21, Jorge
<jo***@jorgechamorro.composted:

>On Jul 19, 6:07 pm, Dr J R Stockton <[e-mail]:

>What does that page report (for various browsers?) on your Mac?

...

>iCab 3.0.5: "Apparent resolution is at least 58 bits."

That one was initially rather unexpected, since Math.random() is
supposed to return an evenly-distributed IEEE Double with an effective
53-bit mantissa, and the best previously seen or reported was 53 bits.

ISO/IEC 16262 only requires that the result of Math.random() be evenly
distributed, not that the resolution be independent of the value.

It appears that other browsers in effect mask the output of the
(64-bit?) PRNG to 53 bits before converting to Double, while iCab does
that only within the conversion itself.

It seems undesirable for there to be unnecessary numerical differences
between browsers; if anyone has contact with those writing future
specifications, then I suggest that they ask for the future spec to have
this uncertainty removed. While iCab in a sense has better randomness,
ISTM that uniformity would be preferable.

The function you observed, Resol, is now Resol1; new Resol3 is similar
but uses only randoms >= 0.5.

--
(c) John Stockton, nr London, UK. ?@merlyn.demon.co.uk Turnpike v6.05 MIME.
Web <URL:http://www.merlyn.demon.co.uk/- FAQish topics, acronyms, & links.
Proper <= 4-line sig. separator as above, a line exactly "-- " (SonOfRFC1036)
Do not Mail News to me. Before a reply, quote with ">" or "" (SonOfRFC1036)

[Jorge]

On Jul 20, 7:32*pm, Dr J R Stockton <[e-mail]:

>
The function you observed, Resol, is now Resol1; new Resol3 is similar
but uses only randoms >= 0.5.

John,

I have retouched your resol1() a little bit. Now it receives a
parameter p, and it doesn't return until the higher resolution found
remains unchanged for p iterations of the loop. It gives higher
readings now.

I have also written a bits() function that finds what is the smaller
power of 2 for which it's true that (2^x) === ((2^x)+1). I think that
that must be the size of the mantissa, or not ?

See it here : http://tinyurl.com/68d9br

These are the numbers I get :

IE 5.2.3 : 53, 53.
FF2, FF3 : 52, 53.
Safari : 30, 53.
Opera 9.51 : 31, 53.
iCab 3.0.5 : 63, 53.

But I don't understand why those numbers are different. And, if the
mantissa is 53 bits (iCab), how can, why does resol1() give 63 ?

Here's the code :

<script>
window.onload= function () {
var resol1= (function (p) {
var x, t, max= 0, i= p;
while (i) {
t= 0, x= Math.random();
while ((x*= 2)%1 0) { // shift left until empty
t++;
}
if (t max) {
max= t, i= p;
} else {
i--;
}
}
return max;
})(1e4);

var bits= (function () {
var x, i= 0;
do {
x= Math.pow(2,++i);
} while (x !== (x+1))
return i;
})();

var test= Math.pow(2,bits);
var text= "resol1() : Maximum resolution is at least "+resol1+"
bits.<br>";
text+= "bits() : "+bits+" -In this browser "+(test+1)+" ===
1+"+test;

(document.body.appendChild(
document.createElement(
'h2'))).innerHTML= text;

};
</script>

Thanks,
--Jorge.

[Jorge]

On Jul 21, 3:35*pm, "C. (http://symcbean.blogspot.com/)"
<[e-mail]:

>
I can get to go back to the server even though the image is cached if
I put it in an iframe with src= the image URL then
document.getElementById("MyIframe").contentWindow. location.reload();

If just a plain location.reload() won't do, if setting img.src+= "?
something" won't do either, then that sounds like a Good Idea...

--Jorge.

[Dr J R Stockton]

In comp.lang.javascript message <0d5ff528-59a3-4bb7-8f48-5df465dce82c@i7
6g2000hsf.googlegroups.com>, Mon, 21 Jul 2008 06:27:24, Jorge
<jo***@jorgechamorro.composted:

>I have also written a bits() function that finds what is the smaller
power of 2 for which it's true that (2^x) === ((2^x)+1). I think that
that must be the size of the mantissa, or not ?

We know that 2^53 is 9007199254740992. A Number, being an IEEE Double
and having a 53-bit mantissa, cannot represent 9007199254740993. But
it's not yet absolutely clear to me whether 2^53+1 MUST evaluate to 2^53
and not to 2^53+2.

It is certain that JavaScript uses IEEE Doubles, and that those consist
of one sign bit, eleven biased-exponent bits, a non-stored "1" bit
leading the mantissa, and fifty-two more mantissa bits. 2^53+1 is the
lowest integer requiring MSB...LSB to be at least 54 bits; the lowest
which cannot be stored exactly.

>These are the numbers I get :

IE 5.2.3 : 53, 53.
FF2, FF3 : 52, 53.
Safari : 30, 53.
Opera 9.51 : 31, 53.
iCab 3.0.5 : 63, 53.

But I don't understand why those numbers are different. And, if the
mantissa is 53 bits (iCab), how can, why does resol1() give 63 ?

I'm not entirely sure, to +/- 1 in the result, whether the algorithms
are ideal. But there are clearly three cases : about 31, about 52, and
about 63.

I suppose that "about 31" are those in which 32-bit processing is
involved - probably a 32-bit generator (which will repeat after 2*32 (or
2^32-1) values). Clearly, given the integer operations such as X|Y and
the use of Number for storage, the JavaScript engine must have
interconverters.

The others probably, but not necessarily, use a 64-bit integer pseudo-
random binary sequence generator of the form
U[n] = (U[n-1]*vast + 1) mod 2^64.

Note that the FPU of a PC has the "comp" type, a 64-bit integer, and the
"Extended" type, with a genuine 64-bit mantissa; and a PC can do 64-bit
integer arithmetic either with comp or with a pair of 32-bit integers.
So the system programmer can calculate U[n], put it into the mantissa of
an Extended with suitable exponent, and ask for conversion to the Double
equivalent. In the conversion, U[n] will lose all its leading zeroes,
and then as many trailing bits as cannot fit into the 53 places
available. The value of the least preserved bit will depend on the
value of the Random generated.

However, that means that the resolution of Math.random depends on the
value generated - which seems undesirable.

Those who think that Math.random should give only multiples of 2^-53
(and will in time give all such values such that 0<=X<1) can instead
mask U[n] to 53 bits before conversion, or round the converted result to
a multiple of 2^-53.

--
(c) John Stockton, near London. *@merlyn.demon.co.uk/?.**********@physics.org
Web <URL:http://www.merlyn.demon.co.uk/- FAQish topics, acronyms, & links.
Correct <= 4-line sig. separator as above, a line precisely "-- " (SoRFC1036)
Do not Mail News to me. Before a reply, quote with ">" or "" (SoRFC1036)

[Jorge]

On Jul 22, 7:08*pm, Thomas 'PointedEars' Lahn <[e-mail]>
wrote:

>
I explained to you before why those alias URLs are unsuitable and
unnecessary in Usenet, and asked you to stop posting them.

Yes Thomas, you did. But I still don't agree with you. Sorry about
that.

Regards,
--Jorge.

[Dr J R Stockton]

In comp.lang.javascript message <48**************@PointedEars.de>, Tue,
22 Jul 2008 19:08:42, Thomas 'PointedEars' Lahn <Po*********@web.de>
posted:

>Jorge wrote:

>"C. (http://symcbean.blogspot.com/)" wrote:

>>However, I think it may be possible to do for the client who just
uploaded the data - since, if they click the 'Refresh' button in the
browser it carries out an unconditional reload of the content. I'm
wanting to emulate this from Javascript.

See here : http://tinyurl.com/6lwmmb

I explained to you before why those alias URLs are unsuitable and
unnecessary in Usenet, and asked you to stop posting them.

I am asking you again to post original URL(s) here instead. As a Google
Groups user who heavily relies on the information in that archive, surely
you can see the advantages in complying with that request.

Why should one be concerned with your alleged convenience in the matter
of compressed URLs when you persistently ignore the convenience of
others by not only providing but insisting upon the briefest of
attributions?

--
(c) John Stockton, nr London UK. ??*@merlyn.demon.co.uk Turnpike v6.05 MIME.
Web <URL:http://www.merlyn.demon.co.uk/- FAQish topics, acronyms, & links.
Check boilerplate spelling -- error is a public sign of incompetence.
Never fully trust an article from a poster who gives no full real name.

[Jorge]

On 22 jul, 00:38, Dr J R Stockton <[e-mail]:

>
I'm not entirely sure, to +/- 1 in the result, whether the algorithms
are ideal. *But there are clearly three cases : about 31, about 52, and
about 63.

What do you think about this :

do {
x*= 2, x-= Math.floor(x), t++;
} while ( x0) // shift left until empty

(?)

--Jorge.

[Dr J R Stockton]

In comp.lang.javascript message <72ddfea4-511a-4a91-9e37-0a8be4328cd3@k3
6g2000pri.googlegroups.com>, Thu, 24 Jul 2008 16:56:10, Jorge
<jo***@jorgechamorro.composted:

>On 22 jul, 00:38, Dr J R Stockton <[e-mail]:

>>
I'm not entirely sure, to +/- 1 in the result, whether the algorithms
are ideal. *But there are clearly three cases : about 31, about 52, and
about 63.

What do you think about this :

do {
x*= 2, x-= Math.floor(x), t++;
} while ( x0) // shift left until empty

It gives an answer one larger than the corresponding part of my code.
That may be better.

--
(c) John Stockton, nr London, UK. ?@merlyn.demon.co.uk Turnpike v6.05 MIME.
Web <URL:http://www.merlyn.demon.co.uk/- FAQish topics, acronyms, & links.

[Dr J R Stockton]

In comp.lang.javascript message <nl**************@invalid.uk.co.demon.me
rlyn.invalid>, Fri, 25 Jul 2008 23:30:59, Dr J R Stockton
<jr*@merlyn.demon.co.ukposted:

>In comp.lang.javascript message <72ddfea4-511a-4a91-9e37-0a8be4328cd3@k3
6g2000pri.googlegroups.com>, Thu, 24 Jul 2008 16:56:10, Jorge
<jo***@jorgechamorro.composted:

>>On 22 jul, 00:38, Dr J R Stockton <[e-mail]:

>>>
I'm not entirely sure, to +/- 1 in the result, whether the algorithms
are ideal. *But there are clearly three cases : about 31, about 52, and
about 63.

What do you think about this :

do {
x*= 2, x-= Math.floor(x), t++;
} while ( x0) // shift left until empty

It gives an answer one larger than the corresponding part of my code.
That may be better.

Or for (x = Math.random(), t = 0 ; x%1 0 ; t++) x *= 2
I have changed <URL:http://www.merlyn.demon.co.uk/js-randm.htm#MR>
subsection "For Your Browser".

I see, in WinXP, Safari & Opera showing as expected for a 32-bit PRBS
converted to Double. Firefox has a PRBS of at least 53 bits, with my
results comparable with Math.random() returning only multiples of 2^-53.
But MSIE apparently can return an odd multiple of 2^-54, which seems
unsound.

ISO/IEC 16262 15.8.2.14 is somewhat liberal in its definition of what
Math.random() should give; but, as in its range the absolute resolution
of Number is lowest (for values of 0.5 and higher) at 2^-53, the
greatest uniformity is obtained by allowing return values of N * 2^-53
for 0 <= N < 2^53. Anything else is less than ideal.

Comments?

--
(c) John Stockton, near London. *@merlyn.demon.co.uk/?.**********@physics.org
Web <URL:http://www.merlyn.demon.co.uk/- FAQish topics, acronyms, & links.
Correct <= 4-line sig. separator as above, a line precisely "-- " (SoRFC1036)
Do not Mail News to me. Before a reply, quote with ">" or "" (SoRFC1036)

[Jorge]

On Jul 27, 2:59*pm, Dr J R Stockton <[e-mail]:

In comp.lang.javascript message <[e-mail]
rlyn.invalid>, Fri, 25 Jul 2008 23:30:59, Dr J R Stockton
<[e-mail]:

In comp.lang.javascript message <72ddfea4-511a-4a91-9e37-0a8be4328cd3@k3
6g2000pri.googlegroups.com>, Thu, 24 Jul 2008 16:56:10, Jorge
<[e-mail]:

>On 22 jul, 00:38, Dr J R Stockton <[e-mail]:

>I'm not entirely sure, to +/- 1 in the result, whether the algorithms
are ideal. *But there are clearly three cases : about 31, about 52,and
about 63.

>What do you think about this :

* * * *do {
* * * * *x*= 2, x-= Math.floor(x), t++;
* * * *} while ( x0) // shift left until empty

It gives an answer one larger than the corresponding part of my code.
That may be better.

Or * *for (x = Math.random(), t = 0 ; x%1 0 ; t++) x *= 2

I have changed <URL:http://www.merlyn.demon.co.uk/js-randm.htm#MR>
subsection "For Your Browser".

I see, in WinXP, Safari & Opera showing as expected for a 32-bit PRBS
converted to Double. *Firefox has a PRBS of at least 53 bits, with my
results comparable with Math.random() returning only multiples of 2^-53.
But MSIE apparently can return an odd multiple of 2^-54, which seems
unsound.

ISO/IEC 16262 15.8.2.14 is somewhat liberal in its definition of what
Math.random() should give; but, as in its range the absolute resolution
of Number is lowest (for values of 0.5 and higher) at 2^-53, the
greatest uniformity is obtained by allowing return values of N * 2^-53
for 0 <= N < 2^53. *Anything else is less than ideal.

Comments?

On a Mac: resolA, resolB, resolC :

Safari 3.1.2: 31,31,31
FF 2.0.0.16 : 53,53,53
FF 3.0.1 : 53,53,53
Opera 9.5.1: 32, 32, 32
IE 5.2.3: 54,53,54
iCab 3.0.5: 64,53,57

--Jorge.

[Jorge]

On Jul 27, 2:59*pm, Dr J R Stockton <[e-mail]:

In comp.lang.javascript message <[e-mail]
rlyn.invalid>, Fri, 25 Jul 2008 23:30:59, Dr J R Stockton
<[e-mail]:

In comp.lang.javascript message <72ddfea4-511a-4a91-9e37-0a8be4328cd3@k3
6g2000pri.googlegroups.com>, Thu, 24 Jul 2008 16:56:10, Jorge
<[e-mail]:

>On 22 jul, 00:38, Dr J R Stockton <[e-mail]:

>I'm not entirely sure, to +/- 1 in the result, whether the algorithms
are ideal. *But there are clearly three cases : about 31, about 52,and
about 63.

>What do you think about this :

* * * *do {
* * * * *x*= 2, x-= Math.floor(x), t++;
* * * *} while ( x0) // shift left until empty

It gives an answer one larger than the corresponding part of my code.
That may be better.

Or * *for (x = Math.random(), t = 0 ; x%1 0 ; t++) x *= 2

I have changed <URL:http://www.merlyn.demon.co.uk/js-randm.htm#MR>
subsection "For Your Browser".

I see, in WinXP, Safari & Opera showing as expected for a 32-bit PRBS
converted to Double. *Firefox has a PRBS of at least 53 bits, with my
results comparable with Math.random() returning only multiples of 2^-53.
But MSIE apparently can return an odd multiple of 2^-54, which seems
unsound.

ISO/IEC 16262 15.8.2.14 is somewhat liberal in its definition of what
Math.random() should give; but, as in its range the absolute resolution
of Number is lowest (for values of 0.5 and higher) at 2^-53, the
greatest uniformity is obtained by allowing return values of N * 2^-53
for 0 <= N < 2^53. *Anything else is less than ideal.

Comments?

On a Mac: resolA, resolB, resolC :

Safari 3.1.2: 31,31,31
FF 2.0.0.16 : 53,53,53
FF 3.0.1 : 53,53,53
Opera 9.5.1: 32, 32, 32
IE 5.2.3: 54,53,54
iCab 3.0.5: 64,53,57

--Jorge.

[Dr J R Stockton]

On Jul 27, 7:42*pm, Jorge <[e-mail]:

On Jul 27, 2:59*pm, Dr J R Stockton <[e-mail]:

I have changed <URL:http://www.merlyn.demon.co.uk/js-randm.htm#MR>
subsection "For Your Browser".

I see, in WinXP, Safari & Opera showing as expected for a 32-bit PRBS
converted to Double. *Firefox has a PRBS of at least 53 bits, with my
results comparable with Math.random() returning only multiples of 2^-53..
But MSIE apparently can return an odd multiple of 2^-54, which seems
unsound.

Comments?

On a Mac: resolA, resolB, resolC :

Safari 3.1.2: 31,31,31
FF 2.0.0.16 : 53,53,53
FF 3.0.1 : 53,53,53
Opera 9.5.1: 32, 32, 32
IE 5.2.3: 54,53,54
iCab 3.0.5: 64,53,57

Thanks; I've updated the page. It may be that with various different
range parameters for ResolC a greater understanding of what iCab is
doing might be obtained. The author of iCab can be found via <http://
www.icab.de/>.

--
(c) John Stockton, near London, UK. Posting with Google.
Mail: J.R.""""""""@physics.org or (better) via Home Page at
Web: <URL:http://www.merlyn.demon.co.uk/>
FAQish topics, acronyms, links, etc.; Date, Delphi, JavaScript, ...

[Jorge]

On Jul 27, 2:59*pm, Dr J R Stockton <[e-mail]:

<[e-mail]:

>What do you think about this :

* * * *do {
* * * * *x*= 2, x-= Math.floor(x), t++;
* * * *} while ( x0) // shift left until empty

Or * *for (x = Math.random(), t = 0 ; x%1 0 ; t++) x *= 2

Or do {} while (t++, (x*= 2)%1 0)

Why there's not an "international obfuscated JavaScript code
contest" ?

--Jorge.

[Dr J R Stockton]

In comp.lang.javascript message <abae3935-396a-4fca-aaf7-ea9e7c832a91@i7
6g2000hsf.googlegroups.com>, Mon, 28 Jul 2008 08:02:04, Jorge
<jo***@jorgechamorro.composted:

>Or do {} while (t++, (x*= 2)%1 0)

or do {t++} while ((x*=2)%1)

>Why there's not an "international obfuscated JavaScript code
contest" ?

You're in it! But that means "count doublings until integer", which
expresses the need rather exactly. Page js-randm.htm again updated;
results as before.

--
(c) John Stockton, nr London, UK. ?@merlyn.demon.co.uk Turnpike v6.05 MIME.
Web <URL:http://www.merlyn.demon.co.uk/- FAQish topics, acronyms, & links.
Proper <= 4-line sig. separator as above, a line exactly "-- " (SonOfRFC1036)
Do not Mail News to me. Before a reply, quote with ">" or "" (SonOfRFC1036)

[Jorge]

On Jul 29, 2:34*pm, Dr J R Stockton <[e-mail]:

>
or * * * do {t++} while ((x*=2)%1)

You got it right. Oh yeah, now that's perfect !

--Jorge.