On Wednesday, February 5, 2003, at 04:24 PM, Dave Abrahams wrote:
Actually there were two problems. One was the one you mentioned above. The other was that we needed either a masking to 32 bits or the type made unsigned to prevent an optimization (integer calculations done on FPU), which led to non-conforming overflow behavior.On Wednesday, February 05, 2003 10:11 AM [GMT+1=CET], Matthias Troyer <[EMAIL PROTECTED]> wrote:I am looking into it but already have a conjecture. When using signed
64 bit integers the Cray compiler (with optimization turned on) uses
the floating point units to actually perform the operations in 46 bit
arithmetic. This speeds up things but causes compatibility problems. In
the case of the jam sources we could avoid this "optimization" by using
unsigned types. Is it possible to use an unsigned integer here to avoid
similar problems?
Just to be clear, we didn't avoid an optimization by using unsigned types.
We avoided undefined behavior due to overflow in signed integers, or
conversions from unsigned->signed.
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