Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote:
[...]
> > > > > > +Also note that the modulo operation often varies by language
> > > > > > +when the dividend or divisor are negative, where Python, Ruby,
> etc.
> > > > > > +differ from C, Go, Java, etc. This specification requires
> > > > > > +that modulo use truncated division (where -13 % 3 == -1) as
> > > > > > +implemented in C, Go,
> > > > > > +etc.:
> > > > > > +
> > > > > > + a % n = a - n * trunc(a / n)
> > > > > > +
> > > > >
> > > > > Interesting bit of info, but I'm not sure how it relates to the ISA doc.
[...]
> Those differences are in signed div/mod only, right?
> Unsigned div/mod doesn't have it, right?
> bpf has only unsigned div/mod.
Ah right, will replace. However since imm is a signed integer, that leaves
an ambiguity that is important to clarify.
What is the expected value for the following 64-bit BPF_DIV operation:
r0 = 0xFFFFFFFFFFFFFFFF
r0 /= -10
Is it 0x1 or 0x10000000a? i.e., is the -10 sign extended to
0xFFFFFFFFFFFFFFF6 or treated as 0xFFFFFFF6 when doing the unsigned
division?
Dave
