https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96859
--- Comment #10 from Steve Kargl <sgk at troutmask dot apl.washington.edu> --- On Tue, Sep 01, 2020 at 03:20:20PM +0000, jakub at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96859 > > --- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> --- > I've read that. But I think in this case it is an obvious bug (just, what > I've > missed in the patch, there is another copy of the same bug in another > routine). > The > /* Clear first bit. */ > if (kind == 1 || kind == 4 || kind == 16) > { > if (buf[0] == '4') > buf[0] = '0'; > else if (buf[0] == '5') > buf[0] = '1'; > else if (buf[0] == '6') > buf[0] = '2'; > else if (buf[0] == '7') > buf[0] = '3'; > } > part looks correct, for kind 1, 4 and 16 the calculated len times 3 is 1 > larger > than the number of bits it needs, so the above ensures that the first digit is > 0-3 even if it is 4-7 by subtracting 4. > But the: > /* Clear first two bits. */ > else > { > if (buf[0] == '4' || buf[0] == '6') > buf[0] = '0'; > else if (buf[0] == '5' || buf[0] == '7') > buf[0] = '1'; > } > which is needed for kind 2 and 8, when he calculated len times 3 is 2 larger > than the number of bits it needs, is only correct for digits 0-1 an 4-7, for > which it ensures the digit is 0 if it is even and 1 if it is odd. But 2 and 3 > are kept as is, while they don't fit into 1 bit. > It is certainly possible I have/had an off-by-one in handwritten conversions I was doing; in particular, I don't often work with octal numbers.
