Messages in this thread | | | From | Dan Streetman <> | Date | Thu, 14 May 2015 04:54:07 -0400 | Subject | Re: [PATCH] lib: fix 842 build on 32-bit architectures |
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On Wed, May 13, 2015 at 7:52 PM, Dan Streetman <ddstreet@ieee.org> 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@ieee.org> > >> >> 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@arndb.de> >> --- >> 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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