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use a table-free clz on coldfire, where it benchmarks a bit faster

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git-svn-id: svn://svn.rockbox.org/rockbox/trunk@19933 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Andrew Mahone 2009-02-06 05:43:00 +00:00
parent a7738a3526
commit 79c25649b7
1 changed files with 39 additions and 0 deletions
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39
apps/plugins/pictureflow.c
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@ -346,11 +346,50 @@ static inline int clz(uint32_t v)
} }
/* Otherwise, use our clz, which can be inlined */ /* Otherwise, use our clz, which can be inlined */
#elif defined(CPU_COLDFIRE)
/* This clz is based on the log2(n) implementation at
* http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
* A clz benchmark plugin showed this to be about 14% faster on coldfire
* than the LUT-based version.
*/
static inline int clz(uint32_t v)
{
int r = 32;
if (v >= 0x10000)
{
v >>= 16;
r -= 16;
}
if (v & 0xff00)
{
v >>= 8;
r -= 8;
}
if (v & 0xf0)
{
v >>= 4;
r -= 4;
}
if (v & 0xc)
{
v >>= 2;
r -= 2;
}
if (v & 2)
{
v >>= 1;
r -= 1;
}
r -= v;
return r;
}
#else #else
static const char clz_lut[16] = { 4, 3, 2, 2, 1, 1, 1, 1, static const char clz_lut[16] = { 4, 3, 2, 2, 1, 1, 1, 1,
0, 0, 0, 0, 0, 0, 0, 0 }; 0, 0, 0, 0, 0, 0, 0, 0 };
/* This clz is based on the log2(n) implementation at /* This clz is based on the log2(n) implementation at
* http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogLookup * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogLookup
* It is not any faster than the one above, but trades 16B in the lookup table
* for a savings of 12B per each inlined call.
*/ */
static inline int clz(uint32_t v) static inline int clz(uint32_t v)
{ {