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slightly faster asm av_log2 for armv6 (currently only Gigabeat S)

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git-svn-id: svn://svn.rockbox.org/rockbox/trunk@23868 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Nils Wallménius 2009-12-06 02:03:03 +00:00
parent 491e0978ec
commit cd22b32450
1 changed files with 14 additions and 2 deletions
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16
apps/codecs/lib/codeclib.h
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@ -76,12 +76,24 @@ unsigned udiv32_arm(unsigned a, unsigned b);
/* TODO figure out if we really need to care about calculating
av_log2(0) */
#if (defined(CPU_ARM) && (ARM_ARCH > 4))
#ifdef CPU_ARM
#if ARM_ARCH > 5
static inline unsigned int av_log2(uint32_t v)
{
unsigned int r;
asm volatile("clz %[r], %[v]\n\t" /* count leading zeroes */
"rsb %[r], %[r], #31\n\t" /* r = 31 - leading zeroes */
"usat %[r], #5, %[r]\n\t" /* unsigned saturate r so -1 -> 0 */
:[r] "=r" (r) : [v] "r" (v));
return(r);
}
#elif ARM_ARCH > 4
static inline unsigned int av_log2(uint32_t v)
{
return v ? 31 - __builtin_clz(v) : 0;
}
#else
#endif
#else /* CPU_ARM */
/* From libavutil/common.h */
extern const uint8_t ff_log2_tab[256] ICONST_ATTR;