Out-of-range decimal literals

Sam Ruby rubys at intertwingly.net
Thu Sep 18 09:17:14 PDT 2008


On Thu, Sep 18, 2008 at 9:49 AM, Sam Ruby <rubys at intertwingly.net> wrote:
> On Thu, Sep 18, 2008 at 9:10 AM, Igor Bukanov <igor at mir2.org> wrote:
>> Should EcmaScript allow decimal literals that cannot be represented as
>> 128-bit decimal? I.e should the following literals give a syntax
>> error:
>>
>> 1.000000000000000000000000000000000000000000000000001m
>> 1e1000000000m ?
>>
>> IMO allowing such literals would just give another source of errors.
>
> Languages have "personalities", and people build up expectations based
> on these characteristics.  As much as possible, I'd like to suggest
> that ECMAScript be internally consistent, and not have one independent
> choice (binary vs decimal) have unexpected implications over another
> (signaling vs quiet operations).

Thinking about it further, rejecting literals with an expressed
precision larger than the underlying data type can support might be
something that could be considered with "use strict", particularly if
applied to both binary and decimal floating point quantities.

> As a tangent, both binary 64 and decimal 128 floating point provide
> "exact" results for a number of operations, they simply do so for
> different domains of numbers.  2**-52 can be represented exactly, for
> example, in binary 64 floating point, but not in decimal 128 floating
> point.  It is only the prevalence of things like decimal literals,
> which naturally are in decimal, which tend to produce inexact but
> correctly rounded values in binary 64 and exact values in decimal 128,
> without a need for rounding.
>
> As to your specific question, here's a few results from my branch of
> SpiderMonkey:
>
> js> 1.000000000000000000000000000000000000000000000000001
> 1
> js> 1e1000000000
> Infinity
> js> 1.000000000000000000000000000000000000000000000000001m
> 1.000000000000000000000000000000000
> js> 1e1000000000m
> Infinity
>
>> Regards, Igor
>
> - Sam Ruby

- Sam Ruby


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