Message 409146 - Python tracker

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Author	steven.daprano
Recipients	cykerway, mark.dickinson, steven.daprano
Date	2021-12-24.14:08:37
SpamBayes Score	-1.0
Marked as misclassified	Yes
Message-id	<1640354917.54.0.0252327554058.issue46173@roundup.psfhosted.org>
In-reply-to

Content
float(x) performs rounding. Only if the value after rounding is out of range is OverflowError raised. M + 1, when correctly rounded to the nearest even float, gives sys.float_info.max. Likewise for M+2, M+3 etc all the way to M+K where K equals 2960 before the correctly rounded result of float(M+K) overflows. Anything less than K=2960 is too small to be distinguished from M when added to it. So there's no bug here, the behaviour is correct for IEEE-754, although perhaps the documentation is misleading. Mark, is my explanation right?

float(x) performs rounding. Only if the value after rounding is out of range is OverflowError raised.

M + 1, when correctly rounded to the nearest even float, gives sys.float_info.max. Likewise for M+2, M+3 etc all the way to M+K where K equals 2**960 before the correctly rounded result of float(M+K) overflows.

Anything less than K=2**960 is too small to be distinguished from M when added to it. So there's no bug here, the behaviour is correct for IEEE-754, although perhaps the documentation is misleading.

Mark, is my explanation right?

History
Date	User	Action	Args
2021-12-24 14:08:37	steven.daprano	set	recipients: + steven.daprano, mark.dickinson, cykerway
2021-12-24 14:08:37	steven.daprano	set	messageid: <1640354917.54.0.0252327554058.issue46173@roundup.psfhosted.org>
2021-12-24 14:08:37	steven.daprano	link	issue46173 messages
2021-12-24 14:08:37	steven.daprano	create