Hi Jay, On Fri, Jul 29, 2011 at 3:59 PM, Jay K <jay.krell@xxxxxxxxxxx> wrote: > > I'm testing signed int32 operations (division, modular reduction, and > > overflow), and came across a floating point exception: > > > int32_t aa = INT32_MIN; > > int32_t bb = -1; > > int32_t rr = aa % bb; > > > > cout << rr << " = " << aa << " % " << bb << endl; > > > There's not much to the command line: `g++ sitest.cpp -o sitest.exe`. > > I was kind of surprised GCC [silently] moved from the integer domain > > to the floating point domain. > > > Is this expected behavior? > > What occurs here is implementation defined. > See also 1 / 0. Thanks. So its apparently undefined for GCC, and its consistent with Seacord's Secure Programming Guide (see INT33-CPP at [1]). Interestingly, using Crypto++ Integers (which don't suffer limited data ranges) and MSVC, both arrive at 0. > Gcc didn't do anything floating point-related. > Integer operations esp. division and mod can have "exceptions" or "traps" or > such. The OS message "Floating point exception" was a bit misleading. (I don't think it was unreasonable to guess the floating point unit generated the floating point exception). > Look at the assembly code. > g++ -S -c sitest.cpp > vi sitest.S You are right - the idiv is there: movl $-2147483648, -4(%rbp) movl $-1, -8(%rbp) movl -4(%rbp), %eax movl %eax, %edx sarl $31, %edx idivl -8(%rbp) Thanks for the help. They were the results I was looking for, I just did not recognize it. Jeff [1] https://www.securecoding.cert.org/confluence/display/cplusplus/INT33-CPP.+Ensure+that+division+and+modulo+operations+do+not+result+in+divide-by-zero+errors
