1161006 - <input type=number> sometimes loses precision for numbers with large numbers of significant digits

Status: RESOLVED INVALID

(Core :: DOM: Core & HTML, defect)

Description

[Al]

User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:37.0) Gecko/20100101 Firefox/37.0
Build ID: 20150415140819

Steps to reproduce:

used input type number with min=8901260000000000000 and max=8901260999999999999


Actual results:

tried typing in 8901260962115482165 but returns 8.90126096211548e+18


Expected results:

value must not be rounded off

Comment 1

[Dave Garrett]

http://www.w3.org/TR/html5/forms.html#number-state-%28type=number%29
http://www.w3.org/TR/html5/infrastructure.html#valid-floating-point-number

Your values exceed the maximum 53-bits that can safely be represented as an integer in a IEEE 754 double-precision floating-point. Max value before rounding is 9007199254740991. This is expected behavior.

See also:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/MAX_SAFE_INTEGER

Comment 2

[Al]

Hi Dave,

If this is true that my values exceed the MAX_SAFE_INTEGER, then why does the following figures behave differently:

1. 8901260962115482112 - Firefox passes the value as is
2. 8901260962115482113 - This is where the rounding off starts
3. 8901260962115482199 - This is the last value that rounds off
4. 8901260962115482200 - Firefox passes the value as is again

Also, is this global? Because it works in Google Chrome.

Thanks,
Alvin

Comment 3

[Jonathan Watt [:jwatt]]

"max safe" means the maximum you can reliably expect to get, not the maximum you will always get.

Comment 5

[Jonathan Watt [:jwatt]]

(In reply to Al from comment #2)
> If this is true that my values exceed the MAX_SAFE_INTEGER, then why does
> the following figures behave differently:
> 
> 1. 8901260962115482112 - Firefox passes the value as is
> 2. 8901260962115482113 - This is where the rounding off starts
> 3. 8901260962115482199 - This is the last value that rounds off
> 4. 8901260962115482200 - Firefox passes the value as is again

Note the difference between input.value and input.valueAsNumber. When you set these values as the value of the 'value' attribute Firefox will try to preserve the string in input.value, but input.valueAsNumber will almost always be a different number. It will only be the same if the binary representation of the number happens to only require 53 significant binary digits because any additional binary digits that might be required would happen to be zeros.

> Also, is this global? Because it works in Google Chrome.

Chrome also tries to preserve any string assigned to the 'value' attribute in the 'value' property, and does a better job that Firefox in this regard (see bug 1005603).

Note also bug 1095539 which may be of interest to you.