Re: [boost] [endian] Project not maintained

Subject: Re: [boost] [endian] Project not maintained
From: Peter Dimov (lists_at_[hidden])
Date: 2016-04-04 13:21:13

Andrey Semashev wrote:

> With (n & 0xFF) you get a bit pattern which on the current architecture is 
> interpreted as a number of 232. This bit pattern may be interpreted 
> differently on another architecture.

That's not very likely. unsigned char with CHAR_BIT == 8 is guaranteed to 
represent the values from 0 to 255. Arbitrary bit permutations or 0:255 -> 
0:255 mappings at the byte level can reasonably be assumed to not exist, or 
if they do, that writing the value of 232 to a file or socket would write 
something there that would be interpreted as 232 on the receiving end.

> If you say that write_be32 is formally portable then it is imperative that 
> the bit pattern it produces is interpreted equivalently on all 
> architectures.

The _bytes_ it produces have the specified values on all architectures. As 
long as writing the byte 232 reads the byte 232, we're clear.

> On a platform with non-IEEE floats, does write_le32 have to convert to 
> IEEE format before producing the bits in p?

Yes.

> What if the x value on the current platform is not representable in IEEE 
> float?

It would put the closest representable IEEE value into the bits in p. Not 
much different from passing a double for x.