this post was submitted on 15 Sep 2024
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Programming

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[–] lysdexic@programming.dev 4 points 2 months ago* (last edited 2 months ago)

Why restrict to 54-bit signed integers?

Because number is a double, and IEEE754 specifies the mantissa of double-precision numbers as 53bits+sign.

Meaning, it's the highest integer precision that a double-precision object can express.

I suppose that makes sense for maximum compatibility, but feels gross if we’re already identifying value types.

It's not about compatibility. It's because JSON only has a number type which covers both floating point and integers, and number is implemented as a double-precision value. If you have to express integers with a double-precision type, when you go beyond 53bits you will start to experience loss of precision, which goes completely against the notion of an integer.