102 lines
2.8 KiB
C++
102 lines
2.8 KiB
C++
// Copyright 2002 and onwards Google Inc.
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//
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// Derived from code by Moses Charikar
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#include "gutil/bits.h"
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#include <assert.h>
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// this array gives the number of bits for any number from 0 to 255
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// (We could make these ints. The tradeoff is size (eg does it overwhelm
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// the cache?) vs efficiency in referencing sub-word-sized array elements)
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const char Bits::num_bits[] = {
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0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,
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1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
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1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
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2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
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1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
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2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
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2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
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3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
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1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
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2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
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2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
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3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
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2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
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3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
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3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
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4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8 };
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int Bits::Count(const void *m, int num_bytes) {
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int nbits = 0;
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const uint8 *s = (const uint8 *) m;
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for (int i = 0; i < num_bytes; i++)
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nbits += num_bits[*s++];
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return nbits;
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}
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int Bits::Difference(const void *m1, const void *m2, int num_bytes) {
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int nbits = 0;
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const uint8 *s1 = (const uint8 *) m1;
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const uint8 *s2 = (const uint8 *) m2;
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for (int i = 0; i < num_bytes; i++)
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nbits += num_bits[(*s1++) ^ (*s2++)];
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return nbits;
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}
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int Bits::CappedDifference(const void *m1, const void *m2,
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int num_bytes, int cap) {
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int nbits = 0;
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const uint8 *s1 = (const uint8 *) m1;
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const uint8 *s2 = (const uint8 *) m2;
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for (int i = 0; i < num_bytes && nbits <= cap; i++)
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nbits += num_bits[(*s1++) ^ (*s2++)];
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return nbits;
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}
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int Bits::Log2Floor_Portable(uint32 n) {
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if (n == 0)
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return -1;
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int log = 0;
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uint32 value = n;
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for (int i = 4; i >= 0; --i) {
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int shift = (1 << i);
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uint32 x = value >> shift;
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if (x != 0) {
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value = x;
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log += shift;
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}
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}
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assert(value == 1);
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return log;
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}
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int Bits::Log2Ceiling(uint32 n) {
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int floor = Log2Floor(n);
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if (n == (n &~ (n - 1))) // zero or a power of two
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return floor;
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else
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return floor + 1;
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}
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int Bits::Log2Ceiling64(uint64 n) {
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int floor = Log2Floor64(n);
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if (n == (n &~ (n - 1))) // zero or a power of two
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return floor;
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else
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return floor + 1;
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}
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int Bits::FindLSBSetNonZero_Portable(uint32 n) {
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int rc = 31;
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for (int i = 4, shift = 1 << 4; i >= 0; --i) {
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const uint32 x = n << shift;
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if (x != 0) {
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n = x;
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rc -= shift;
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}
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shift >>= 1;
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}
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return rc;
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}
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