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A better count_leading_zeros() function, courtesy of Jens Arnold

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git-svn-id: svn://svn.rockbox.org/rockbox/trunk@8577 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Dave Chapman 2006-02-05 09:12:57 +00:00
parent f9df934d90
commit 1a03c37947
1 changed files with 27 additions and 37 deletions
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64
apps/codecs/libalac/alac.c
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@ -184,50 +184,40 @@ static inline void unreadbits(alac_file *alac, int bits)
alac->input_buffer_bitaccumulator *= -1; alac->input_buffer_bitaccumulator *= -1;
} }
static const unsigned char bittab[16] ICONST_ATTR = {
0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4
};
static inline int count_leading_zeros(int input) static inline int count_leading_zeros(int input)
{ {
int output = 0; int output = 32;
int curbyte = 0;
curbyte = input >> 24; #if 0
if (curbyte) goto found; /* Experimentation has shown that the following test is always false,
output += 8; so we don't bother to perform it. */
if (input & 0xffff0000)
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))
{ {
output += 4; input >>= 16;
output -= 16;
} }
else #endif
curbyte >>= 4; if (input & 0xff00)
{
if (curbyte & 0x8) input >>= 8;
return output; output -= 8;
if (curbyte & 0x4) }
return output + 1; if (input & 0xf0)
if (curbyte & 0x2) {
return output + 2; input >>= 4;
if (curbyte & 0x1) output -= 4;
return output + 3; }
output -= bittab[input];
/* shouldn't get here: */ return output;
return output + 4;
} }
void basterdised_rice_decompress(alac_file *alac, void basterdised_rice_decompress(alac_file *alac,
int32_t *output_buffer, int32_t *output_buffer,
int output_size, int output_size,