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nsforge/gist:8949790

Created February 12, 2014 03:51
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Demonstration of uint64 accuracy bug in NSJSONSerialization
Raw
gistfile1.m
NSString *jsonString = @"{\"myNumber\":1029742590268606522}";
NSData *jsonData = [jsonString dataUsingEncoding:NSUTF8StringEncoding];
NSDictionary *jsonDict = [NSJSONSerialization JSONObjectWithData:jsonData options:0 error:NULL];
NSLog(@"jsonDict: %@", jsonDict);
uint64_t myNumber = [jsonDict[@"myNumber"] unsignedLongLongValue];
NSLog(@"myNumber: %llu", myNumber);
/*
Output:
2014-02-12 14:47:54.850 Untitled 11[94676:507] jsonDict: {
myNumber = 1029742590268606522;
}
2014-02-12 14:47:54.852 Untitled 11[94676:507] myNumber: 1029742590268606464
Explanation:
NSJSONSerialization is inappropriately using NSDecimalNumber instead of a standard long long
unsigned NSNumber, and NSDecimalNumber has a bug where getting very large integers out of an
NSDecimalNumber loses accuracy since it uses .doubleValue as in interim representation
(http://stackoverflow.com/a/6713550/86046).
*/
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