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Extend av_log2 in codeclib into a generic for scanning for set bits, which can provide either log2 or leading-zero-count output, and can force mapping 0 input to 0 output if needed (otherwise 0 input produces undefined result). Replace av_log2 in lib/codeclib.h, floor_log2 and wl_min_lzc in libfaad/common.c and common.h, and count_leading_zeros in libalac/alac.c with macros using bs_generic.

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git-svn-id: svn://svn.rockbox.org/rockbox/trunk@23903 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Andrew Mahone 2009-12-09 02:24:45 +00:00
parent 3683bb67db
commit 85aad9b397
6 changed files with 96 additions and 141 deletions
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109
apps/codecs/lib/codeclib.h
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@ -74,45 +74,80 @@ unsigned udiv32_arm(unsigned a, unsigned b);
#define UDIV32(a, b) (a / b)
#endif
#if !defined(CPU_ARM) || ARM_ARCH < 5
/* From libavutil/common.h */
extern const uint8_t bs_log2_tab[256] ICONST_ATTR;
extern const uint8_t bs_clz_tab[256] ICONST_ATTR;
#endif
#define BS_LOG2 0 /* default personality, equivalent floor(log2(x)) */
#define BS_CLZ 1 /* alternate personality, Count Leading Zeros */
#define BS_SHORT 2 /* input guaranteed not to exceed 16 bits */
#define BS_0_0 4 /* guarantee mapping of 0 input to 0 output */
/* Generic bit-scanning function, used to wrap platform CLZ instruction or
scan-and-lookup code, and to provide control over output for 0 inputs. */
static inline unsigned int bs_generic(unsigned int v, int mode)
{
#if defined(CPU_ARM) && ARM_ARCH >= 5
unsigned int r = __builtin_clz(v);
if (mode & BS_CLZ)
{
if (mode & BS_0_0)
r &= 31;
} else {
r = 31 - r;
/* If mode is constant, this is a single conditional instruction */
if (mode & BS_0_0 && (signed)r < 0)
r += 1;
}
#else
const uint8_t *bs_tab;
unsigned int r;
unsigned int n = v;
int inc;
/* Set up table, increment, and initial result value based on
personality. */
if (mode & BS_CLZ)
{
bs_tab = bs_clz_tab;
r = 24;
inc = -16;
} else {
bs_tab = bs_log2_tab;
r = 0;
inc = 16;
}
if (!(mode & BS_SHORT) && n >= 0x10000) {
n >>= 16;
r += inc;
}
if (n > 0xff) {
n >>= 8;
r += inc / 2;
}
#ifdef CPU_COLDFIRE
/* The high 24 bits of n are guaranteed empty after the above, so a
superfluous ext.b instruction can be saved by loading the LUT value over
n with asm */
asm volatile (
"move.b (%1,%0.l),%0"
: "+d" (n)
: "a" (bs_tab)
);
#else
n = bs_tab[n];
#endif
r += n;
if (mode & BS_CLZ && mode & BS_0_0 && v == 0)
r = 0;
#endif
return r;
}
/* TODO figure out if we really need to care about calculating
av_log2(0) */
#if defined(CPU_ARM) && ARM_ARCH >= 6
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 defined(CPU_ARM) && ARM_ARCH >= 5
static inline unsigned int av_log2(uint32_t v)
{
return v ? 31 - __builtin_clz(v) : 0;
}
#else /* CPU_ARM */
/* From libavutil/common.h */
extern const uint8_t ff_log2_tab[256] ICONST_ATTR;
static inline unsigned int av_log2(unsigned int v)
{
int n;
n = 0;
if (v & 0xffff0000) {
v >>= 16;
n += 16;
}
if (v & 0xff00) {
v >>= 8;
n += 8;
}
n += ff_log2_tab[v];
return n;
}
#endif
#define av_log2(v) bs_generic(v, BS_0_0)
/* Various codec helper functions */