Le 29/01/2015 18:36, Alexandre Torres Porres a écrit :
more that 7 digit but less than 8 digits
...
so, 4/3 =! 1.33333 but 4/3 == 1.33333333 (8 "3")
I don't get it. More than 7 decimal digits but less than 8 decimal digits?
yes about 7.22 as Claude pointed : log(2^24-1) 2^24-1 is the max value coded in 23bit, log(x) compute the number of digit of a number. unfortunately, the result is not an integer.
How does that work? In practice, is it 7 or 8?
in practice, number are rounded to the closest value that can be represented in this format.
forget about the comma : the max number that can be represented without exponent is 2^24-1 (max value of 23bits) i.e 16777215 in this case, 8 correct digits if you add 1, it should be 16777216, but that need 24 bit, and it's not possible in a float. so it's noted 1677722 * 10^1 ...
In the example we see that 4/3 == 1.33333333 (8 "3") - so it's 8 decimal digits...
better to say a 9 digit number.
I have a work around using expr. Just put the number in parenthesis.
Try [expr 4./3 == (1.33333333)] (8 "3")
but the thing is that this is also true - [expr 4./3 == (1.3333333)] - also equal to 7 "3"
7 "3", mean 8 digits number: max precision of a float-> no surprise.
cheers c
cheers
2015-01-29 14:58 GMT-02:00 Cyrille Henry <ch@chnry.net mailto:ch@chnry.net>:
hello, ok, claude was faster to answer, but since i already write my mail, i send it anyway... pd internal resolution is float32. (i.e, 23 bit, so a bit less than 17 millions, i.e more that 7 digit but less than 8 digits) pd graphical representation is 6 digits so, 4/3 =! 1.33333 but 4/3 == 1.33333333 (8 "3") even if both are represented with the same number of 3... this is a generic problem of computer float. the only odd thing concerning pd is that number are also saved with 6 digit. (so precision can be lost when a patch is saved) try the attachment patch. then save the patch, and open it back, and see that precision is lost. (I have to modifies the patch as text file to have this behaviors, but you can also have the save precision when creating an object... until you save/load the patch) you can also have a look on the top right of the patch: a weird effect of float precision... cheers c Le 29/01/2015 17:17, Alexandre Torres Porres a écrit : Well, thanks everyone. And now for some related issues. Pd can only represent up to 6 significant digits, so they say. For example, in a message, you can have a number with up to 5 decimal places, like: -5.29314e+12 but it does have a better internal resolution, if you compare 4 / 3 to 1.33333 you'll see 4 / 3 is higher ( try [expr 4./3 > 1.33333] and check). So, what's this internal resolution? And why can't you have the same resolution in a message? thanks 2015-01-28 16:06 GMT-02:00 Martin Peach <chakekatzil@gmail.com <mailto:chakekatzil@gmail.com> <mailto:chakekatzil@gmail.com <mailto:chakekatzil@gmail.com>>__>: On Wed, Jan 28, 2015 at 12:00 PM, Cyrille Henry <ch@chnry.net <mailto:ch@chnry.net> <mailto:ch@chnry.net <mailto:ch@chnry.net>>> wrote: Le 28/01/2015 17:47, Alexandre Torres Porres a écrit : > it's a limitation of 32 bit float I thought so, but same happens when I use the new Pd Vanilla 64 bits... this mean that it's compiled for 64 bit CPU, not that float are store on 64 bits Also last time I checked, Pd saves floats by first printing them to 6 digit precision, so they have even less range than a 'float' type. You could use an object made with pdlua to manipulate large floating-point numbers, as there is no(?) limit to the size of a float in lua. Martin _________________________________________________ Pd-list@lists.iem.at <mailto:Pd-list@lists.iem.at> <mailto:Pd-list@lists.iem.at <mailto:Pd-list@lists.iem.at>> mailing list UNSUBSCRIBE and account-management -> http://lists.puredata.info/__listinfo/pd-list <http://lists.puredata.info/listinfo/pd-list>