[CELT-dev] get_required_bits32() and alloca() -> corrupted stack

[Bjoern Rasmussen]

Ah, that fixed it, thank you!
 
-- Bjoern

----------------------------------------
> Date: Sat, 11 Apr 2009 09:53:55 -0400
> From: tterribe at email.unc.edu
> To: bjoern_rasmussen at hotmail.com
> CC: celt-dev at xiph.org
> Subject: Re: [CELT-dev] get_required_bits32() and alloca() -> corrupted stack
>
> Bjoern Rasmussen wrote:
>> HiI'm trying to run CELT on Win32 but I'm running into some corrupted stack errors when using
>> alloca(). When get_required_bits32() (in file cwrs.c:308) is called
> from get_required_bits()
>> (in file cwrs.c:328) the 'K' parameter is 1 which means that the
> uint32 which is allocated on
>> the stack only has 3 bytes instead of 4. This results in a corrupted
> stack in the following
>> call to log2_frac().Shouldn't the line
> cwrs.c:313:ALLOC(u,K+2,celt_uint32_t);Instead
>> say:ALLOC(u,max(K+2,sizeof(celt_uint32_t)),celt_uint32_t);?-- Bjoern
>
> If you are really using alloca, then ALLOC should be #define'd to
> (stack_alloc.h:99):
>
> var = ((type*)alloca(sizeof(type)*(size)))
>
> So ALLOC(u,K+2,celt_uint32_t) should allocate 12 bytes when K=1. The
> actual cause appears to be a micro-optimization violating one of our
> assumptions in unext32() when called from ncwrs_u32 (cwrs.c:220). Try
> the following patch and let me know if it fixes your problem:
>
> diff --git a/libcelt/cwrs.c b/libcelt/cwrs.c
> index f44fca1..aa2a732 100644
> --- a/libcelt/cwrs.c
> +++ b/libcelt/cwrs.c
> @@ -217,7 +217,7 @@ celt_uint32_t ncwrs_u32(int _n,int _m,celt_uint32_t
> *_u){
> k=2;
> do _u[k]=(k< while(++k> - for(k=2;k<_n;k++)unext32(_u+2,_m,(k< + for(k=2;k }
> else{
> celt_uint32_t um1;
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