According to the ECMAScript specification, numbers are stored in IEEE
754 floating point format (52-bit fraction, 11-bit biased exponent, and
a 1-bit sign).
The language does not support integers at all, so there is no chance of
representing a 64 bit integer.
The number you got (9007199254740992) is near enough to 2^53, which is
about what you should expect.
Andrew
Leif W wrote:
Hello,
I don't know if anyone has followed the bug report for 1232705. An
issue is raised about big integer support. For the purposes of this
context, big integers shall be anything bigger than 32-bits, either
signed or unsigned, and may herein be expressed in either hex or
decimal (preferably both).
The biggest/smallest integer I can get in Mozilla Firefox on WinXP 32
is +/- hex 20 0000 0000 0000 or dec 9007199254740992. I have not
tested in Linux yet. Can anyone on other OSes or browsers get bigger
or smaller numbers? I wrote a simply JavaScript to help, and attached
it to the bug report.
The JavaScript page merely has some buttons with predefined numbers,
an input field, a parse button, and an output field. The "parse"
button takes the string representation in the input text field, passes
it to parseInt to make an integer. Then it assigns that integer to
the value of the output text field, which implicitly converts back to
a string. The strings expect decimal only at this point. I could do
bin2hex and hex2bin later.
The strings should be the same. I haven't got an algorithm to do this
automatically. I did it manually. I just started with all 9s, (9,
99, 999, and so on) until the results differed. Then I reduced the
first 9 to 1, and the rest of the 9s to 0s. Then I increased the last
digit from 0 through 9 to ensure they were all the same. If it's the
same, go half way up, else go half way down on the most significant
digit until you isolate the highest you can make it. For example,
take the first digit from 1 to 5, and the last from 0-9. If it' the
same, take the first up to 7, last 0-9. I found that sometimes the
number would (seemingly at random) match and then differ with the last
digit changes. If this happens, it's considered an overflow
somewhere. Usually the overflow caused the least significant digit(s)
to go to 0. But sometimes it would make odds round down to evens,
usually 2 or 0 though.
It's hard to explain. If you come up with a good algorithm, let me
know. I think it would be handy to have a quick, automatic way of
determining your browser's math limits. Either way, if you've got
about 5-10 minutes to kill, please test this. You can easily start
off where I was to save time. A dec <-> hex converter might be handy,
so if it might be useful, I'll include later. The odd looking decimal
number held little meaning for me until I converted it to hex and was
surprised to find a pretty number, which I don't believe is
coincidence. :p It's probably a C #define in some header file of
some math library in Mozilla. Simply making it bigger and recompiling
might work locally, but does nothing for the default installs out
there. Maybe there's an archaic way to change it in some browser
config file. But I kind of doubt that.
Leif
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