Hi Wolfgang,
On 08/09/11 07:14, Wolfgang Denk wrote:
> Dear Che-liang Chiou,
>
> In message
> <canjuy2+bb7ta70vhotq3lja-o4ymgcsdp9pnfzrx-uwret7...@mail.gmail.com> you
> wrote:
>>
>> So I guess we can agree that a 64-bit divider is feature that is nice
>> to have, and we should decide:
>> * Do we need a 64-64 bit divider or a 64-32 bit one?
>> * Do we write it in C or assembly?
>
> The situation is simple: there is no code in U-Boot that needs this
> feature, and we try to avoid adding dead code.
>
> If you don;t have a use case at hand that actually requires this, then
> please let's drop it.
You'll laugh at this - the Intel High Performance Event Timers (HPET) are
defined to a resolution of femto-seconds and you end up with code in
get_timer() like:
u32 count_low;
u32 count_high;
u32 fs_per_tick;
u64 ticks;
u64 fs;
u32 ms;
count_low = readl(&hpet_registers->main_count_low);
count_high = readl(&hpet_registers->main_count_high);
fs_per_tick = readl(&hpet_registers->counter_clk_period);
ticks = ((u64)count_high << 32) | ((u64)count_low);
fs = fs_per_tick * ticks;
ms = (u32)lldiv(ticks, 1000000000000);
But I can right shift both divisor and dividend by 12 bits without loosing
any significant precision which turns it into:
ms = (u32)lldiv(ticks >> 12, 244140625);
So I almost needed a 64 bit divisor.
Regards,
Graeme
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