[FFmpeg-devel] [PATCH 09/12] WMA: store level_table as floats, use type punning for sign flip in decode

[Måns Rullgård]

Alex Converse <alex.converse at gmail.com> writes:

> On Sun, Sep 27, 2009 at 6:49 AM, Mans Rullgard <mans at mansr.com> wrote:
>> ---
>> ?libavcodec/wma.c ? ? ? ?| ? 19 +++++++++++++------
>> ?libavcodec/wma.h ? ? ? ?| ? ?4 ++--
>> ?libavcodec/wmaprodata.h | ? ?4 ++--
>> ?libavcodec/wmaprodec.c ?| ? ?2 +-
>> ?4 files changed, 18 insertions(+), 11 deletions(-)
>>
>
>> @@ -465,19 +469,22 @@ unsigned int ff_wma_get_large_val(GetBitContext* gb)
>> ?*/
>> ?int ff_wma_run_level_decode(AVCodecContext* avctx, GetBitContext* gb,
>> ? ? ? ? ? ? ? ? ? ? ? ? ? ? VLC *vlc,
>> - ? ? ? ? ? ? ? ? ? ? ? ? ? ?const uint16_t *level_table, const uint16_t *run_table,
>> + ? ? ? ? ? ? ? ? ? ? ? ? ? ?const float *level_table, const uint16_t *run_table,
>> ? ? ? ? ? ? ? ? ? ? ? ? ? ? int version, WMACoef *ptr, int offset,
>> ? ? ? ? ? ? ? ? ? ? ? ? ? ? int num_coefs, int block_len, int frame_len_bits,
>> ? ? ? ? ? ? ? ? ? ? ? ? ? ? int coef_nb_bits)
>> ?{
>> ? ? int code, level, sign;
>> + ? ?const uint32_t *ilvl = (const uint32_t*)level_table;
>> + ? ?uint32_t *iptr = (uint32_t*)ptr;
>> ? ? const unsigned int coef_mask = block_len - 1;
>> ? ? for (; offset < num_coefs; offset++) {
>> ? ? ? ? code = get_vlc2(gb, vlc->table, VLCBITS, VLCMAX);
>> ? ? ? ? if (code > 1) {
>> ? ? ? ? ? ? /** normal code */
>> ? ? ? ? ? ? offset += run_table[code];
>
> Is this legitimate under strict aliasing rules?

Probably not, but I don't think it's possible for a compiler to mess
it up.  Even so, if someone has a suggestion for how to make it
kosher, I'm all ears.

-- 
M?ns Rullg?rd
mans at mansr.com