Added rank function implementation.

cxxmph/mph_bits.cc

@@ -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]; }
+
+
+
 }

cxxmph/mph_bits.h

@@ -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
 

cxxmph/mph_bits_test.cc

@@ -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 (rank64(0) != 0) exit(-1);
-  if (ranktable[0] != 0) exit(-1);
+  if (rank64(1) != 1) exit(-1);
-  if (ranktable[1] != 1) exit(-1);
+  if (rank64(2) != 1) exit(-1);
-  if (ranktable[2] != 1) exit(-1);
+  if (rank64(255) != 8) exit(-1);
-  if (ranktable[255] != 8) exit(-1);
 }