On Wed, May 13, 2015 at 7:52 PM, Dan Streetman <ddstreet@xxxxxxxx> wrote:
>> Building the 842 code on 32-bit ARM currently results in this link
>> error:
>>
>> ERROR: "__aeabi_uldivmod" [lib/842/842_decompress.ko] undefined!
>
> Oops! Guess I should build/test on 32 bit more.
>
>>
>> The reason is that the __do_index function performs a 64-bit
>> division by a power-of-two number, but it has no insight into
>> the function arguments.
wait, do you mean the 64 bit mod, total % fsize? That should already
be fixed in Herbert's tree, I changed it to subtraction instead.
In any case, I looked at the code again and I think the fsize
parameter can be removed, and just simply calculated in the function,
it's just a shift. I'll send a patch.
>>
>> By marking that function inline, the fsize argument is always
>> known at the time that do_index is called, and the compiler is
>> able to replace the extremely expensive 64-bit division with
>> a cheap constant shift operation.
>
> alternately, we know that fsize will always be less than 64 bits,
> at most it's 4<<9 or 8<<8 (both == 1<<11). So we could just change
> its type to u16.
>
> diff --git a/lib/842/842_decompress.c b/lib/842/842_decompress.c
> index 6b2b45aecde3..285bf6b6959c 100644
> --- a/lib/842/842_decompress.c
> +++ b/lib/842/842_decompress.c
> @@ -169,7 +169,7 @@ static int do_data(struct sw842_param *p, u8 n)
> return 0;
> }
>
> -static int __do_index(struct sw842_param *p, u8 size, u8 bits, u64 fsize)
> +static int __do_index(struct sw842_param *p, u8 size, u8 bits, u16 fsize)
> {
> u64 index, offset, total = round_down(p->out - p->ostart, 8);
> int ret;
>
> Or, we could inline it and change the type to u16. In any case,
>
> Acked-by: Dan Streetman <ddstreet@xxxxxxxx>
>
>>
>> Aside from fixing that link error, this approach should also improve
>> both code size and performance on 32-bit architectures significantly.
>>
>> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
>> ---
>> Found while building arm32 allmodconfig with gcc-5.0
>>
>> diff --git a/lib/842/842_decompress.c b/lib/842/842_decompress.c
>> index 6b2b45aecde3..285bf6b6959c 100644
>> --- a/lib/842/842_decompress.c
>> +++ b/lib/842/842_decompress.c
>> @@ -169,7 +169,7 @@ static int do_data(struct sw842_param *p, u8 n)
>> return 0;
>> }
>>
>> -static int __do_index(struct sw842_param *p, u8 size, u8 bits, u64 fsize)
>> +static inline int __do_index(struct sw842_param *p, u8 size, u8 bits, u64 fsize)
>> {
>> u64 index, offset, total = round_down(p->out - p->ostart, 8);
>> int ret;
>>
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