Re: [PATCH] ibex_uart: fix XOR-as-pow

[Eric Blake]

On 6/23/20 2:54 PM, Paolo Bonzini wrote:
> The xor-as-pow warning in clang actually detected a genuine bug.
> Fix it.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>   hw/char/ibex_uart.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/char/ibex_uart.c b/hw/char/ibex_uart.c
> index 3e0dd9968e..45cd724998 100644
> --- a/hw/char/ibex_uart.c
> +++ b/hw/char/ibex_uart.c
> @@ -331,7 +331,7 @@ static void ibex_uart_write(void *opaque, hwaddr addr,
>           if (value & UART_CTRL_NCO) {
>               uint64_t baud = ((value & UART_CTRL_NCO) >> 16);
>               baud *= 1000;
> -            baud /= 2 ^ 20;
> +            baud >>= 20;

Dividing by 1M instead of 22 seems much more logical, indeed :)
It's odd that we are scaling up by 1000, down by 1024*1024, then

>   
>               s->char_tx_time = (NANOSECONDS_PER_SECOND / baud) * 10;

inverting and scaling by 10.  I don't know if there is a more succinct 
way to write the intended transformation.

>           }

But even without reading the hardware manual to see if the resulting 
scaling is correct, the typo fix is obvious enough to give:
Reviewed-by: Eric Blake <eblake@redhat.com>

--
Eric Blake, Principal Software Engineer
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