Trial-division code runs 2x faster as 32-bit on Windows than 64-bit on Linux

Question

I have a piece of code that runs 2x faster on windows than on linux. Here are the times I measured:

g++ -Ofast -march=native -m64
    29.1123
g++ -Ofast -mar         


        

Answer 1

Extracted answer from the edited question:

It was caused by building 32b binaries on windows as opposed to 64b binaries on linux, here are 64b numbers for windows:

Visual studio 2013 Debug 64b
    29.1985
Visual studio 2013 Release 64b
    29.7469