Summation on HP 42S

[Albert Chan]

(09-29-2018 09:10 PM)ijabbott Wrote:  Curiously, replacing `i += i;` with `i <<= 1` in the code ... it just returns the value 31.

Perhaps << operator assumed unsigned integer (bits operation) ?
To confirm, this unsigned version also work: i += (unsigned) i

My head tends to think of C int like the CPU, with two-complement wrapping.
Just to be safe, now I add -fwrapv flag to my makefile.

BTW, older GCC does not optimize this aggressively ...
Using *old* GCC 3.4.2, even with -O3, it return the "expected" 31.

Update: above bug, failing with newer GCC, is often called time bomb.
https://www.cs.utah.edu/~regehr/papers/overflow12.pdf