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Topic: Upscaling an IEEE754 subnormal number to be normal
Replies: 6   Last Post: Oct 19, 2017 11:32 AM

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Damian McGuckin

Posts: 4
Registered: 6/17/15
Upscaling an IEEE754 subnormal number to be normal
Posted: Oct 17, 2017 7:54 PM
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Given an IEEE 754 number with a significand of size 'p', what is the smallest scaling factor that is guaranteed to bvring it into the normal range.

I would have thought that this was simply 2^p. When I take the smallest subnormal double and float, i.e. a '1' in the least significant bit of the mantissa, all zeros in the exponent and sign field, and multiply by 2^p (as a double or float), I get a number which has a non-zero exponent, i.e. normal.

However, reviewing some versions of the source code of 'frexp' seem to suggest that it is has to be instead 2^(p+2).

Why is this and what am I missing here?

Thanks - Damian

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