NSNumberFormatter stringFromNumber returns incorrectly rounded value

Number:rdar://18468186 Date Originated:2014-09-26
Status:Open Resolved:
Product:iOS, OS X Product Version:iOS 8, OS X 10.10
Classification:Serious Bug Reproducible:Always
NSNumberFormatter stringFromNumber returns an incorrectly rounded value on iOS 8 and OS X 10.10. Previous iOS and OS X releases returned the correct value.

The issue seems to be related to the usesSignificantDigits  and maximumSignificantDigits set on the formatter.

According to the API documentation[1] maximumSignificantDigits will only be used when usesSignificantDigits is set to YES. It appears that maximumSignificantDigits is being used regardless of the usesSignificantDigits value.

[1] https://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Classes/NSNumberFormatter_Class/index.html#//apple_ref/occ/instp/NSNumberFormatter/usesSignificantDigits

Steps to Reproduce:
1. Create an NSNumberFormatter
    NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];

2. Set the properties on the formatter
    [formatter setUsesSignificantDigits:NO];
    [formatter setMaximumSignificantDigits:2];

3. Create a number to format
    NSNumber *number = @(291.99);

4. Format the number
    NSString *formattedNumber = [formatter stringFromNumber:number];

Expected Results:
formattedNumber should contain @"292".

Actual Results:
formattedNumber contains @"290".

iOS 8 [12A365], OS X 10.10 [14A361c]

Not device specific.


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