Math.PI.toString(16) -> 3.243f6a8885a3 and back
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From: Benjamin 'BeRo' Rosseaux on 21 Jun 2010 17:07 Am 21.06.2010 22:50, schrieb Scott Sauyet: > I saw the exponent code, and am not quite sure how that should play > with bases higher than 14 (it gets tricky when you consider that > "1.0e3", base 10, should convert to 1000 but "1.0e3", base 16, should > convert to 1.055419921875. The question is what does "e" represent? "e" is the exponent char at least for base 10, which will can generate at least at "9.8.1 ToString Applied to the Number Type" in the ES5 spec. At radix larger than 14, the "e" exponent char will ignored, and at radix larger than 25, the "p" exponent char will ignored. > But do you foresee a need for multiple consecutive minus/plus signs? And the other with the multiple minus/plus signs is just for to be foolproof-safe, and can be changed easy, if needed.
From: Scott Sauyet on 21 Jun 2010 17:27 Benjamin 'BeRo' Rosseaux wrote: > Am 21.06.2010 22:50, schrieb Scott Sauyet: >> I saw the exponent code, and am not quite sure how that should play >> with bases higher than 14 (it gets tricky when you consider that >> "1.0e3", base 10, should convert to 1000 but "1.0e3", base 16, should >> convert to 1.055419921875. The question is what does "e" represent? > > "e" is the exponent char at least for base 10, which will can generate > at least at "9.8.1 ToString Applied to the Number Type" in the ES5 spec. > At radix larger than 14, the "e" exponent char will ignored, and at > radix larger than 25, the "p" exponent char will ignored. This might be the best approach, but it certainly feels awkward. In any case, your approach is similar to the one I posted. Yours iterates forward over the fractional digits, versus mine which went backwards. It seems to gain the same additional precision over other approaches that mine does. But it doesn't round badly on 0.fgr, base 36 as mine did. Definitely a nice version. I'm wondering if it will round badly on other short strings, but I haven't done any serious tests. In a separate post, I will detail a slightly different approach I've been trying which is intended to clean up the likely (although untested) performance problems in my earlier version and avoid the rounding errors with shorter strings. -- Scott
From: Scott Sauyet on 21 Jun 2010 17:44 Scott Sauyet wrote: > Dr J R Stockton wrote: >> Also, parsFlotC is in hand. > > I look forward to it. I need to find a little time for my next > approach, but I do have a new idea as well. I've found a little time finally, and the new approach definitely seems an improvement, both in the actual results and the likely performance considerations. I no longer lazily load the regexes needed, as I have to save some other values for each base and it made sense just to compute them together. I keep a list of the powers of each base less than or equal to 2^53. I still have a separate parseFraction function, but instead of working digit-by-digit, it calls parseInt on chunks of as many digits as will fit inside 2^53. It's not well-tested yet, but I've posted it on my latest test page, here: <http://scott.sauyet.com/Javascript/Test/2010-06-21b/> The PHP source is at <http://scott.sauyet.com/Javascript/Test/2010-06-21b/index.phps> Here is the function: var parseFloat_ss2 = (function() { var origPF = parseFloat, DEPTH = 2, maxInt = Math.pow(2, 53), allDigits = "0123456789abcdefghijklmnopqrstuvwxyz", regexes = [null, null], powers = [null, null], parseFraction = function(str, base) { if (!str) return 0; var basePowers = powers[base], max = basePowers[basePowers.length - 1]; total = 0, denominator = 1, count = 0; while (str.length && count < DEPTH) { var index = Math.min(str.length, basePowers.length - 1); total += parseInt(str.substring(0, index), base) / (denominator * basePowers[index]); str = str.substring(index); denominator *= max; count++; } return total; }; (function() { for (var base = 2; base <=36; base++) { var digits = allDigits.substring(0, base); regexes[base]= new RegExp("(^[\\-\\+]?)([" + digits + "]*)(?:\\.([" + digits + "]*))?$", "i"); powers[base] = []; var power = 1, i = 0; while (power <= maxInt) { powers[base][i] = power; power *= base; i++; } } }()); return function (str, base) { if (!base || base == 10) return origPF(str); if ((base < 2) || (base > 36) || (base % 1)) return NaN; var regex = regexes[base], match = regex.exec(str); if (!match) return NaN; return ((match[1] == "-") ? -1 : 1) * ( (match[2] == "" ? 0 : parseInt(match[2], base)) + parseFraction(match[3], base) ); }; }()); -- Scott
From: Dr J R Stockton on 22 Jun 2010 12:01 In comp.lang.javascript message <7550eef3-42f2-4d97-9459-dea2356aa84b(a)z8 g2000yqz.googlegroups.com>, Mon, 21 Jun 2010 13:50:01, Scott Sauyet <scott.sauyet(a)gmail.com> posted: >I saw the exponent code, and am not quite sure how that should play >with bases higher than 14 (it gets tricky when you consider that >"1.0e3", base 10, should convert to 1000 but "1.0e3", base 16, should >convert to 1.055419921875. The question is what does "e" represent? In a browser, a full function parseFloat(String, radix) should accept the exponent format which, in that browser, toString(radix) gives for sufficiently large and small Numbers. But it should accept that format for all finite values, and with the radical point not in the same position. -- (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 estrdate.htm js-dates.htm pas-time.htm critdate.htm etc.
From: Dr J R Stockton on 22 Jun 2010 12:47
In comp.lang.javascript message <703e1d78-8204-4c60-b73f-eac7de238028(a)j4 g2000yqh.googlegroups.com>, Mon, 21 Jun 2010 12:51:53, Scott Sauyet <scott.sauyet(a)gmail.com> posted: >Dr J R Stockton wrote: >> Consider putting the test button somewhere that the >> "value" does not cover when showing a list, and putting >> the results below, rather than beside, the input. > >I don't understand the first part of that. What browser has the >button covering something important? The button was covered, in part, by the dropped list. > Does the latest version fix the >UI versions you mention? > > <http://scott.sauyet.com/Javascript/Test/2010-06-21a/> Yes. But you set the width to 800px. I have a 1280*1024 screen which is a little bigger than A4 landscape. But I like to be able to work with an editor (A5 portrait) on one side of the screen and material-to-read in A5 portrait on the other side. That means that my browser is normally set by <input type=button value=ReSize onClick="window.resizeTo(640, window.screen.height*0.85)"> in its home page; and, for browsers where resize does not work, that page has a fixed-width Table between a pair of <hr> so I pull the side of the window until the lines and table match. Code which I edit gets a default 72-character line marking; I write a little shorter so that it fits into my displays, and then of course it fits News. In Opera, one can edit the source copy. You page is nearly OK with min- width 300 px and actual width 640 px ; a slight reduction in margin or padding would make it OK. I'm not, of course, saying that you should set 640 px width; just that with an unspecified width and economy of margins a reader gets more choice. Where you have more than one function from a person, I suggest that the first be numbered "1". My ExactPF us now called BetterPF for two reasons, one being that it is not invariably exact. -- (c) John Stockton, nr London, UK. ?@merlyn.demon.co.uk Turnpike v6.05 MIME. Web <URL:http://www.merlyn.demon.co.uk/> - FAQqish topics, acronyms & links; Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc. No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News. |