[XviD-devel] Endian Problem found

[Christoph Nägeli]

Hello,

Since the xvid_bench quant test looked a little strange I had a look at 
the code (run on a PowerPC):

  =====  test quant =====
PLAINC -   quant_mpeg_intra 101.431 usec       crc32=0x750b840e | ERROR
PLAINC -   quant_mpeg_inter 104.775 usec       crc32=0x0b895346 | ERROR
PLAINC - dequant_mpeg_intra 53.767 usec       crc32=0x2f2cb029 | ERROR
PLAINC - dequant_mpeg_inter 65.915 usec       crc32=0x4b64700b | ERROR
PLAINC -   quant_h263_intra 39.888 usec       crc32=0x99380911 | ERROR
PLAINC -   quant_h263_inter 44.091 usec       crc32=0x9d1bb0e2 | ERROR
PLAINC - dequant_h263_intra 46.557 usec       crc32=0x66f1a2e5 | ERROR
PLAINC - dequant_h263_inter 43.007 usec       crc32=0x565a0e26 | ERROR

I found (or think I found) the problem in
uint32_t calc_crc(uint8_t *mem, int len, uint32_t initial);

The first Pointer is declared in the caller as uint16_t.
In the Preprocessor Macro DO#, The mem pointer gets read byte by byte, 
since it's actually a uint16_t the right way to read it on a big-endian 
would be [1] [0] [3] [2] ... (right?)

So I changed the function to test if this is the only problem. As I 
know that the len is always a multiple of 64 in this file, I made the 
following changes:

#define DO2(c, crc) ((crc) = crc32tab[((unsigned int)((crc)>>24) ^ 
(c[1])) & 0xff] ^ ((crc) << 8)); \
                     ((crc) = crc32tab[((unsigned int)((crc)>>24) ^ 
(c[0])) & 0xff] ^ ((crc) << 8))

uint32_t
calc_crc(uint8_t *mem, int len, uint32_t initial)
{
     register unsigned int crc;

     crc = initial;

     while(len >= 2) {
         DO2(mem, crc);
         mem += 2;
         len -= 2;
     }

     return crc;
}

With this code, the test runcs successfully. Has anyone an idea how to 
change it that it works if the 'len' isn't a multiple of 2?
And what if the mem is really a uint8_t* or uint32_t* (the code above 
wouldn't work for that)?


Christoph


Test result with the code above:

  =====  test quant =====
PLAINC -   quant_mpeg_intra 100.195 usec       crc32=0xfd6a21a4
PLAINC -   quant_mpeg_inter 104.684 usec       crc32=0xf6de7757
PLAINC - dequant_mpeg_intra 51.418 usec       crc32=0x2def7bc7
PLAINC - dequant_mpeg_inter 64.169 usec       crc32=0xd878c722
PLAINC -   quant_h263_intra 41.068 usec       crc32=0x2eba9d43
PLAINC -   quant_h263_inter 39.234 usec       crc32=0xbd315a7e
PLAINC - dequant_h263_intra 44.601 usec       crc32=0x9841212a
PLAINC - dequant_h263_inter 40.860 usec       crc32=0xe7df8fba
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