[lwip-devel] [bug #51447] Sequence number comparisons invoke undefined behavior

[Stian Sebastian Skjelstad]

Follow-up Comment #2, bug #51447 (project lwip):

typecasting between s32_t and u32_t is not undefined behaviour. On (almost
all) systems, CPU work in 2nd compliments and the only differences about u32_t
and s32_t are which branch instructions or which comparison instruction to
use. 

The only situations where unwanted results might occur is when going from
16bit into 32bit. Example: u16_t into s32_t will cause numbers to not be
signed extended (-1 will become 0x0000ffff for example).

The current macro will for example detect sequence number 0x00000004 to come
after 0xfffffffe, since it only looks at the delta, ignoring that it has
wrapped around zero.


In which situation does the current macro fail to give the correct result? 



(file #41185)
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Additional Item Attachment:

File name: u32.c                          Size:0 KB


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