diff options
Diffstat (limited to 'src/H5Vprivate.h')
| -rw-r--r-- | src/H5Vprivate.h | 89 |
1 files changed, 78 insertions, 11 deletions
diff --git a/src/H5Vprivate.h b/src/H5Vprivate.h index 2deaeaf..71f62b0 100644 --- a/src/H5Vprivate.h +++ b/src/H5Vprivate.h @@ -300,14 +300,84 @@ H5V_vector_inc(int n, hsize_t *v1, const hsize_t *v2) while (n--) *v1++ += *v2++; } +/* Lookup table for general log2(n) routine */ +static const char LogTable256[] = +{ + 0, 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, + 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, + 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, + 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, + 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, + 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, + 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, + 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, + 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, + 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, + 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, + 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, + 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, + 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, + 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, + 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7 +}; + /*------------------------------------------------------------------------- - * Function: H5V_power_of_two + * Function: H5V_log2_gen * * Purpose: Determines the log base two of a number (i.e. log2(n)). + * (i.e. the highest bit set in a number) + * + * Note: This is from the "Bit Twiddling Hacks" at: + * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogLookup + * + * The version on the web-site is for 32-bit quantities and this + * version has been extended for 64-bit quantities. + * + * Return: log2(n) (always - no failure condition) + * + * Programmer: Quincey Koziol + * Monday, March 6, 2006 * - * Note: N must be a power of two and is limited to 32-bit quantities. + *------------------------------------------------------------------------- + */ +static H5_inline unsigned UNUSED +H5V_log2_gen(hsize_t n) +{ + unsigned r = 0; /* r will be log2(n) */ + register unsigned int t, tt, ttt; /* temporaries */ + + if((ttt = n >> 32)) + if((tt = n >> 48)) + r = (t = n >> 56) ? 56 + LogTable256[t] : 48 + LogTable256[tt & 0xFF]; + else + r = (t = n >> 40) ? 40 + LogTable256[t] : 32 + LogTable256[ttt & 0xFF]; + else + if((tt = n >> 16)) + r = (t = n >> 24) ? 24 + LogTable256[t] : 16 + LogTable256[tt & 0xFF]; + else + r = (t = n >> 8) ? 8 + LogTable256[t] : LogTable256[n]; + + return(r); +} /* H5V_log2_gen() */ + + +/* Lookup table for specialized log2(n) of power of two routine */ +static const unsigned MultiplyDeBruijnBitPosition[32] = +{ + 0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8, + 31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9 +}; + +/*------------------------------------------------------------------------- + * Function: H5V_log2_of2 + * + * Purpose: Determines the log base two of a number (i.e. log2(n)). + * (i.e. the highest bit set in a number) + * + * Note: **N must be a power of two** and is limited to 32-bit quantities. + * * This is from the "Bit Twiddling Hacks" at: * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogDeBruijn * @@ -318,17 +388,14 @@ H5V_vector_inc(int n, hsize_t *v1, const hsize_t *v2) * *------------------------------------------------------------------------- */ -static H5_inline unsigned -H5V_log2(uint32_t n) +static H5_inline unsigned UNUSED +H5V_log2_of2(uint32_t n) { - static const unsigned MultiplyDeBruijnBitPosition[32] = - { - 0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8, - 31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9 - }; - +#ifndef NDEBUG + HDassert(POWER_OF_TWO(n)); +#endif /* NDEBUG */ return(MultiplyDeBruijnBitPosition[(n * (uint32_t)0x077CB531UL) >> 27]); -} /* H5V_log2() */ +} /* H5V_log2_of2() */ #endif /* H5Vprivate_H */ |