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Optimised C version of count_leading_zeros() taken from alac-0.1.1. This makes ALAC very close to realtime on the ipod (just the very occasional skip during disk reading - it is realtime when the disk is sleeping).

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git-svn-id: svn://svn.rockbox.org/rockbox/trunk@8545 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Dave Chapman 2006-02-03 08:27:53 +00:00
parent d2e75bf02d
commit 347992e9d9
1 changed files with 39 additions and 9 deletions
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48
apps/codecs/libalac/alac.c
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@ -184,18 +184,48 @@ static inline void unreadbits(alac_file *alac, int bits)
alac->input_buffer_bitaccumulator *= -1;
}
/* hideously inefficient. could use a bitmask search,
* alternatively bsr on x86,
*/
static inline int count_leading_zeros(int32_t input)
static inline int count_leading_zeros(int input)
{
int i = 0;
while (!(0x80000000 & input) && i < 32)
int output = 0;
int curbyte = 0;
curbyte = input >> 24;
if (curbyte) goto found;
output += 8;
curbyte = input >> 16;
if (curbyte & 0xff) goto found;
output += 8;
curbyte = input >> 8;
if (curbyte & 0xff) goto found;
output += 8;
curbyte = input;
if (curbyte & 0xff) goto found;
output += 8;
return output;
found:
if (!(curbyte & 0xf0))
{
i++;
input = input << 1;
output += 4;
}
return i;
else
curbyte >>= 4;
if (curbyte & 0x8)
return output;
if (curbyte & 0x4)
return output + 1;
if (curbyte & 0x2)
return output + 2;
if (curbyte & 0x1)
return output + 3;
/* shouldn't get here: */
return output + 4;
}
void basterdised_rice_decompress(alac_file *alac,