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Added rank function implementation.

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This commit is contained in:
Davi Reis 2012-03-21 20:19:16 -03:00
parent 86dccdb466
commit 9375a15dd4
3 changed files with 33 additions and 24 deletions
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21
cxxmph/mph_bits.cc
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@ -4,4 +4,25 @@ namespace cxxmph {
const uint8_t dynamic_2bitset::vmask[] = { 0xfc, 0xf3, 0xcf, 0x3f};
template <int n, int mask = (1 << 7)> struct bitcount {
enum { value = (n & mask ? 1:0) + bitcount<n, (mask >> 1)>::value };
};
template <int n> struct bitcount<n, 0> { enum { value = 0 }; };
template <int size, int index = size>
class CompileTimeRankTable {
public:
CompileTimeRankTable() : current(bitcount<index - 1>::value) { }
uint8_t operator[] (uint8_t i) { return *(&current + size - i - 1); }
private:
unsigned char current;
CompileTimeRankTable<index -1> next;
};
template <int size> class CompileTimeRankTable<size, 0> { };
static CompileTimeRankTable<256> kRanktable;
uint8_t Ranktable::get(uint8_t i) { return kRanktable[i]; }
}

25
cxxmph/mph_bits.h
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@ -62,30 +62,19 @@ static uint32_t nextpoweroftwo(uint32_t k) {
for (int i=1; i<sizeof(uint32_t)*CHAR_BIT; i<<=1) k = k | k >> i;
return k+1;
}
template <int n, int mask = (1 << 7)> struct bitcount {
enum { value = (n & mask ? 1:0) + bitcount<n, (mask >> 1)>::value };
};
template <int n> struct bitcount<n, 0> { enum { value = 0 }; };
template <int size, int index = size>
class CompileTimeRankTable {
public:
CompileTimeRankTable() : current(bitcount<index - 1>::value) { }
int operator[] (int i) { return *(&current + size - i - 1); }
private:
unsigned char current;
CompileTimeRankTable<index -1> next;
};
template <int size> class CompileTimeRankTable<size, 0> { };
typedef CompileTimeRankTable<256> Ranktable;
// Interesting bit tricks that might end up here:
// http://graphics.stanford.edu/~seander/bithacks.html#ZeroInWord
// Fast a % (k*2^t)
// http://www.azillionmonkeys.com/qed/adiv.html
// rank and select:
// http://vigna.dsi.unimi.it/ftp/papers/Broadword.pdf
struct Ranktable { static uint8_t get(uint8_t); };
static uint8_t rank64(uint64_t bits) {
auto bytes = reinterpret_cast<const uint8_t*>(&bits);
return Ranktable::get(bytes[0]) + Ranktable::get(bytes[1]) +
Ranktable::get(bytes[2]) + Ranktable::get(bytes[3]);
};
} // namespace cxxmph

11
cxxmph/mph_bits_test.cc
View File

@ -4,7 +4,7 @@
#include "mph_bits.h"
using cxxmph::dynamic_2bitset;
using cxxmph::Ranktable;
using cxxmph::rank64;
int main(int argc, char** argv) {
dynamic_2bitset small(256, true);
@ -55,11 +55,10 @@ int main(int argc, char** argv) {
dynamic_2bitset large(1000, true);
empty.swap(large);
Ranktable ranktable;
if (ranktable[0] != 0) exit(-1);
if (ranktable[1] != 1) exit(-1);
if (ranktable[2] != 1) exit(-1);
if (ranktable[255] != 8) exit(-1);
if (rank64(0) != 0) exit(-1);
if (rank64(1) != 1) exit(-1);
if (rank64(2) != 1) exit(-1);
if (rank64(255) != 8) exit(-1);
}