[PATCH] ipsum_calc_block: Optimize size and speed

[Joakim Tjernlund]

Joakim Tjernlund/Transmode wrote on 2010/04/23 16:14:58:
>
> >
> > Hello!
> >
> > > But you can't get rid of:
> > >  z + (z < sum)
> > > which is the real bottleneck. Perhaps this doesn't cost much
> > > on high end CPUs but it sure does on embedded CPUs
> >
> > Why should it be?  It can be compiled as a sequence of "add with carry"
> > instructions, can't it?
> Yes, but have you seen gcc do that? I havn't, perhaps gcc has become smarter
> recently?
>
>      Jocke

Just tried this and it didn't with gcc 3.4.3 on PowerPC
Some arch does not have an add with carry insn(MIPS?)

      Jocke

unsigned long
add32(unsigned long sum, unsigned long x)
{
  unsigned long z = sum + x;
  return z + (z < sum);
}

/* gcc -O3 -S gives:

	.file	"addc.c"
	.gnu_attribute 4, 2
	.gnu_attribute 8, 1
	.section	".text"
	.align 2
	.globl add32
	.type	add32, @function