[FFmpeg-devel] [PATCH] dsputil: add bswap16_buf()

[Måns Rullgård]

Michael Niedermayer <michaelni at gmx.at> writes:

> On Sun, Jun 13, 2010 at 05:59:20PM +0100, Mans Rullgard wrote:
>> ---
>>  libavcodec/dsputil.c |    7 +++++++
>>  libavcodec/dsputil.h |    1 +
>>  2 files changed, 8 insertions(+), 0 deletions(-)
>> 
>> diff --git a/libavcodec/dsputil.c b/libavcodec/dsputil.c
>> index 0701324..1ecd73f 100644
>> --- a/libavcodec/dsputil.c
>> +++ b/libavcodec/dsputil.c
>> @@ -260,6 +260,12 @@ static void bswap_buf(uint32_t *dst, const uint32_t *src, int w){
>>      }
>>  }
>>  
>> +static void bswap16_buf(uint16_t *dst, const uint16_t *src, int len)
>> +{
>> +    while (len--)
>> +        *dst++ = bswap_16(*src++);
>> +}
>
> on 64bit arch this is likely faster:
>
> uint64_t u= ((uint64_t*)src)[i];
> ((uint64_t*)dst)[i]= ((u>>8)&0x...) + ((u<<8)&0x...)

That depends entirely on the specifics of the machine, but point taken.
It would also in general require 8-byte alignment.  Not sure if that
can be guaranteed.

The purpose of having this in dsputil is to allow optimised
implementations for specific machines.  A 32-bit block bswap function
already exists, and some patch posted was doing a 16-bit block swap.
If one makes sense, so does the other.

>>  static int sse4_c(void *v, uint8_t * pix1, uint8_t * pix2, int line_size, int h)
>>  {
>>      int s, i;
>> @@ -4455,6 +4461,7 @@ av_cold void dsputil_init(DSPContext* c, AVCodecContext *avctx)
>>      c->add_hfyu_left_prediction  = add_hfyu_left_prediction_c;
>>      c->add_hfyu_left_prediction_bgr32 = add_hfyu_left_prediction_bgr32_c;
>>      c->bswap_buf= bswap_buf;
>> +    c->bswap16_buf = bswap16_buf;
>>  #if CONFIG_PNG_DECODER
>>      c->add_png_paeth_prediction= ff_add_png_paeth_prediction;
>>  #endif
>> diff --git a/libavcodec/dsputil.h b/libavcodec/dsputil.h
>> index fd2d07f..f3926cd 100644
>> --- a/libavcodec/dsputil.h
>> +++ b/libavcodec/dsputil.h
>> @@ -365,6 +365,7 @@ typedef struct DSPContext {
>>      /* this might write to dst[w] */
>>      void (*add_png_paeth_prediction)(uint8_t *dst, uint8_t *src, uint8_t *top, int w, int bpp);
>>      void (*bswap_buf)(uint32_t *dst, const uint32_t *src, int w);
>
>> +    void (*bswap16_buf)(uint16_t *dst, const uint16_t *src, int len);
>
> how much alignment can we assume to have for dst/src? and len?

I don't know as I haven't located every place that could use this
function.

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