Walter: > bearophile wrote: > > Walter: > > > >> Look at the asm dump of a function. It's full of add's - not only ADD > >> instructions, but addressing mode multiplies and add's. Subtraction is > >> often expressed in terms of addition, relying on twos-complement > >> wraparound. > > > > This answer is a bit relevant only if the programmer is using inline asm, > > while the discussion was about unsigned differences in D code, that are > > uncommon in my D code. Sometimes I even assign lengths to signed-word > > variables, to avoid some signed/unsigned comparison bugs. > > A lot of the addition is also carried out at link time, and even by the > loader. > Subtraction is done by relying on overflow.
The back-end carries out my D operations using unsigned differences on CPU registers, the linker has to use them, etc. But the discussion was about explicit operations done by the D code written by the programmer. Modular arithmetic done by unsigned fixed bitfields is mathematically sound, but it's a bit too much bug-prone for normal Safe D modules :-) Bye, bearophile
