[MPlayer-dev-eng] Fwd: [MPlayer-users] Work done twice: problems in libswscale assembly optimization codes

[Guillaume POIRIER]

The below message is more appropriate in this mailing list, so I'm
forwarding it here...

---------- Forwarded message ----------
From: Netex <netex at 163.com>
Date: Jan 5, 2007 10:04 AM
Subject: [MPlayer-users] Work done twice: problems in libswscale
assembly optimization codes
To: "MPlayer usage questions, feature requests,  bug reports"
<mplayer-users at mplayerhq.hu>


Hi,

Today I read libswscale codes and found there are problems in #ifdef's
branching. See the code:

static inline void RENAME(rgb32to24)(const uint8_t *src,uint8_t
*dst,long src_size)
{
  uint8_t *dest = dst;
  const uint8_t *s = src;
  const uint8_t *end;
#ifdef HAVE_MMX
  const uint8_t *mm_end;
#endif
  end = s + src_size;
#ifdef HAVE_MMX
  // ...MMX Codes...
#endif
  while(s < end)
  {
#ifdef WORDS_BIGENDIAN
    /* RGB32 (= A,B,G,R) -> RGB24 (= R,G,B) */
    s++;
    dest[2] = *s++;
    dest[1] = *s++;
    dest[0] = *s++;
    dest += 3;
#else
    *dest++ = *s++;
    *dest++ = *s++;
    *dest++ = *s++;
    s++;
#endif
  }
}

If HAVE_MMX is not defined, the code equals to:

static inline void RENAME(rgb32to24)(const uint8_t *src,uint8_t
*dst,long src_size)
{
  uint8_t *dest = dst;
  const uint8_t *s = src;
  const uint8_t *end;
  end = s + src_size;
  while(s < end)
  {
#ifdef WORDS_BIGENDIAN
    /* RGB32 (= A,B,G,R) -> RGB24 (= R,G,B) */
    s++;
    dest[2] = *s++;
    dest[1] = *s++;
    dest[0] = *s++;
    dest += 3;
#else
    *dest++ = *s++;
    *dest++ = *s++;
    *dest++ = *s++;
    s++;
#endif
  }
}

If HAVE_MMX is defined, the code equals to:

static inline void RENAME(rgb32to24)(const uint8_t *src,uint8_t
*dst,long src_size)
{
  uint8_t *dest = dst;
  const uint8_t *s = src;
  const uint8_t *end;
  const uint8_t *mm_end;
  end = s + src_size;
  // ...MMX Codes...
  while(s < end)
  {
#ifdef WORDS_BIGENDIAN
    /* RGB32 (= A,B,G,R) -> RGB24 (= R,G,B) */
    s++;
    dest[2] = *s++;
    dest[1] = *s++;
    dest[0] = *s++;
    dest += 3;
#else
    *dest++ = *s++;
    *dest++ = *s++;
    *dest++ = *s++;
    s++;
#endif
  }
}

So the work are done *TWICE*. Am I too stupid?

--
netex at 163.com



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