On Fri, 2003-10-31 at 13:23, David S. Miller wrote:
> we're as mystified as you are as to why it is that:
> if (sum & 0x10000) {
> sum++;
> sum &= 0xffff;
> }
> works while:
> sum = ((sym >> 16) + sum) & 0xffff;
> does not. The theory was that it might be some x86 gcc bug,
> but looking at the assembler diff Arnaldo Carvalho de Melo
> (the appletalk maintainer) showed me between the before and
> after:
> xorl %eax, %eax
> - decl %ecx
> movb (%ebx), %al
> - incl %ebx
> addl %eax, %edx
> addl %edx, %edx
> - movl %edx, %eax
> - shrl $16, %eax
> - addl %edx, %eax
> - movzwl %ax,%edx
> + testl $65536, %edx
> + je .L982
> + incl %edx
> + andl $65535, %edx
> +.L982:
> + decl %ecx
> + incl %ebx
> cmpl $-1, %ecx
>
> we still can't see what's wrong.
> He did confirm that the change in question makes IPX compute checksums
> correctly.
If so, something major is WRONG.
Code all over the place would need this "fix".
Was an old NG Sniffer being used to verify this?
Sniffer had a long term problem with IPX checksums.
Has the gcc team been contacted?
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