thank you, i'll come back later with sample code On Wednesday, June 26, 2019 at 1:56:34 PM UTC+8, Leszek Swirski wrote: > > To be clear: both C++ and JS use the exact same "double" representation, > neither is more precise than the other. In fact we use the exact same > machine instructions to feel with them. The significant digits/decimal > digits mentioned are when printing, not when calculating. > > So, if it's not x87 extra precision, then it must either be a non exact > translation from C++ to JavaScript, or a bug. If you have a small repro > that demonstrates the difference, then please file a bug and we'll take a > look. > > - Leszek > > > On Wed, 26 Jun 2019, 06:00 Jerry Jin, <[email protected] <javascript:>> > wrote: > >> thank you, i googled around and found msvc double is using 64-bit sse, >> not x87 fpu >> >> not sure if it's because c++ double has 16 significant figures and js has >> 15 >> >> On Tuesday, June 25, 2019 at 8:51:58 PM UTC+8, Jakob Kummerow wrote: >>> >>> If your original C++ code uses doubles, then porting it to >>> TypeScript/JavaScript should be possible without loss of accuracy (and >>> using plain built-in Numbers, no external libraries). If you have a >>> reproducible counter-example, it would be interesting to hear about the >>> details. >>> >>> The only exception I can think of is if your C++ compiler decided to >>> emit x87 FPU code (on x86 hardware) which would use 80 bits (instead of 64 >>> bits) for intermediate results. But I don't think modern compilers still do >>> that; they should emit 64-bit SSE instructions. >>> >>> Side note: modern JavaScript has BigInts, which have arbitrary >>> precision, but only integer values. So they're probably not useful for your >>> case, but depending on what problem you're solving, you might be able to >>> reformulate it to use integers. >>> >>> >>> On Tue, Jun 25, 2019 at 2:19 PM Dan Elphick <[email protected]> >>> wrote: >>> >>>> On Tuesday, June 25, 2019 at 10:24:56 AM UTC+1, Jerry Jin wrote: >>>>> >>>>> Hello, >>>>> I'm new to v8-dev, sorry if this was already asked before. >>>>> >>>>> my problem is, i re-implemented a c++ numerical lib using typescript, >>>>> and some test cases failed due to float number not having enough accuracy >>>>> (i debugged js/c++ code side by side with chrome devtool&msvc) >>>>> right now, my only option is to user third party lib like `decimal.js` >>>>> >>>>> i wonder is there any way to increase float number accuracy like c++ >>>>> double type? >>>>> >>>> >>>>> example, is there anyway to store more than 15 decimal places in number >>>>> >>>> >>>> Javascript and V8 already use doubles to represent floating point >>>> numbers. However double precision floating point numbers can have about 16 >>>> significant figures, so it's not possible to get any more accuracy using >>>> C++ double. You may be able to print more than that (e.g. pi.ToFixed(30) >>>> but they won't be accurate beyond 15 decimal places. >>>> >>>> >>>>> ``` >>>>> > let pi = 3.141592653589793238462643383280; >>>>> < undefined >>>>> > pi >>>>> < 3.141592653589793 >>>>> ``` >>>>> >>>>> not sure if this is possible in v8, if yes, where should i start? >>>>> >>>>> thanks! >>>>> >>>> -- >>>> -- >>>> v8-dev mailing list >>>> [email protected] >>>> http://groups.google.com/group/v8-dev >>>> --- >>>> You received this message because you are subscribed to the Google >>>> Groups "v8-dev" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to [email protected]. >>>> To view this discussion on the web visit >>>> https://groups.google.com/d/msgid/v8-dev/cfed0633-c6e7-45c4-a5c0-ca9f6cfaec9a%40googlegroups.com >>>> >>>> <https://groups.google.com/d/msgid/v8-dev/cfed0633-c6e7-45c4-a5c0-ca9f6cfaec9a%40googlegroups.com?utm_medium=email&utm_source=footer> >>>> . >>>> For more options, visit https://groups.google.com/d/optout. >>>> >>> -- >> -- >> v8-dev mailing list >> [email protected] <javascript:> >> http://groups.google.com/group/v8-dev >> --- >> You received this message because you are subscribed to the Google Groups >> "v8-dev" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected] <javascript:>. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/v8-dev/bc1e8872-a93a-405b-94b7-0a8ad01e24f2%40googlegroups.com >> >> <https://groups.google.com/d/msgid/v8-dev/bc1e8872-a93a-405b-94b7-0a8ad01e24f2%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> For more options, visit https://groups.google.com/d/optout. >> >
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