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Add a generic code for all targets for CLZ

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Patrick Pelissier committed 2017-11-12 09:38:14 +01:00
1 parent 446fa7d35f
commit 5615a1419a
1 file changed
+45 -1
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m-genint.h
+45 -1
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@@ -76,10 +76,54 @@ static inline void genint_clear(genint_t s)
s->data = NULL;
}
#if defined(__GNUC__) && (__GNUC__*100 + __GNUC_MINOR__) >= 304
static inline unsigned int m_core_clz(unsigned long limb)
{
return limb == 0 ? GENINT_LIMBSIZE : __builtin_clzl(limb);
return M_UNLIKELY (limb == 0) ? sizeof(unsigned long)*CHAR_BIT : __builtin_clzl(limb);
}
#else
#define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
static inline unsigned int m_core_clz(unsigned long limb)
{
unsigned int shift = 0;
/* This code should be branchless on most targets */
#if ULONG_MAX == 18446744073709551615UL
/* Compute shift so that, it is
+ -7 if the highest 56 bits are clear,
+ -6 for the highest 48 bits,
+ -5 for the highest 40 bits,
+ -4 for the highest 32 bits,
+ -3 for the highest 24 bits,
+ -2 for the highest 16 bits,
+ -1 for the highest 8 bits,
+ 0 otherwise */
shift = -(limb < 0x100000000000000UL);
shift -= (limb < 0x1000000000000UL);
shift -= (limb < 0x10000000000UL);
shift -= (limb < 0x100000000UL);
shift -= (limb < 0x1000000UL);
shift -= (limb < 0x10000UL);
shift -= (limb < 0x100UL);
shift = shift*8 + 56;
shift = 56 - shift + M_CORE_CLZ_TAB[limb >> shift ];
#elif ULONG_MAX == 4294967295UL
/* Compute shift so that, it is
+ -3 if the highest 24 bits are clear,
+ -2 for the highest 16 bits,
+ -1 for the highest 8 bits,
+ 0 otherwise */
shift = -(limb < 0x1000000UL);
shift -= (limb < 0x10000UL);
shift -= (limb < 0x100UL);
shift = shift*8 + 24;
shift = 24 - shift + M_CORE_CLZ_TAB[limb >> shift ];
#else
# error Unkown size for unsigned long. Please create a bug report and report the ULONG_MAX value.
#endif
return shift;
}
#endif
static inline size_t genint_pop(genint_t s)
{