Bug report

Bug description:

importstructf=struct.unpack(">d",bytes.fromhex("7FF0000000080001"))[0]print(f)# nanf2=struct.unpack(">f",struct.pack(">f",f))[0]print(f2)# inf

Repeating this withFFF0000000080001 you'll seenan turn into-inf.

This only happens in Python 3.14+ (not 3.13). I'm pretty sure that this fix is causing it:#130317

Preserving the signaling/quieting bit is a great idea, I find. But since the mantissa is being truncated, onemust ensure that the narrower width mantissa doesn't end up being all0 bits as that representsinf instead ofnan.

CPython versions tested on:

3.14

Operating systems tested on:

Linux

Linked PRs

• gh-141042: fix sNaN's packing for mixed floating-point formats #141107