[issue1621] Do not assume signed integer overflow behavior

[Antti Haapala]

Antti Haapala added the comment:

One common case where signed integer overflow has been assumed has been the wraparound/overflow checks like in http://bugs.python.org/issue27473 

I propose that such commonly erroneous tasks such as overflow checks be implemented as common macros in CPython as getting them right is not quite easy (http://c-faq.com/misc/sd26.html); it would also make the C code more self-documenting.

Thus instead of writing

     if (va.len > PY_SSIZE_T_MAX - vb.len) {
  
one would write something like
    
    if (PY_SSIZE_T_SUM_OVERFLOWS(va.len, vb.len)) {

and the mere fact that such a macro *wasn't* used there would signal about possible problems with the comparison.

----------
nosy: +ztane

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue1621>
_______________________________________