// Copyright 2002 and onwards Google Inc.

//

// Derived from code by Moses Charikar

#include "gutil/bits.h"

#include <assert.h>

// this array gives the number of bits for any number from 0 to 255

// (We could make these ints.  The tradeoff is size (eg does it overwhelm

// the cache?) vs efficiency in referencing sub-word-sized array elements)

const char Bits::num_bits[] = {

        0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4, 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3,

        4, 4, 5, 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4,

        4, 5, 4, 5, 5, 6, 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, 2, 3, 3, 4, 3, 4, 4,

        5, 3, 4, 4, 5, 4, 5, 5, 6, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, 3, 4, 4, 5,

        4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, 2,

        3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5,

        5, 6, 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4,

        5, 4, 5, 5, 6, 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, 3, 4, 4, 5, 4, 5, 5, 6,

        4, 5, 5, 6, 5, 6, 6, 7, 4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8};

int Bits::Count(const void* m, int num_bytes) {

    int nbits = 0;

    const uint8* s = (const uint8*)m;

    for (int i = 0; i < num_bytes; i++) nbits += num_bits[*s++];

    return nbits;

}

int Bits::Difference(const void* m1, const void* m2, int num_bytes) {

    int nbits = 0;

    const uint8* s1 = (const uint8*)m1;

    const uint8* s2 = (const uint8*)m2;

    for (int i = 0; i < num_bytes; i++) nbits += num_bits[(*s1++) ^ (*s2++)];

    return nbits;

}

int Bits::CappedDifference(const void* m1, const void* m2, int num_bytes, int cap) {

    int nbits = 0;

    const uint8* s1 = (const uint8*)m1;

    const uint8* s2 = (const uint8*)m2;

    for (int i = 0; i < num_bytes && nbits <= cap; i++) nbits += num_bits[(*s1++) ^ (*s2++)];

    return nbits;

}

int Bits::Log2Floor_Portable(uint32 n) {

    if (n == 0) return -1;

    int log = 0;

    uint32 value = n;

    for (int i = 4; i >= 0; --i) {

        int shift = (1 << i);

        uint32 x = value >> shift;

        if (x != 0) {

            value = x;

            log += shift;

        }

    }

    assert(value == 1);

    return log;

}

int Bits::Log2Ceiling(uint32 n) {

    int floor = Log2Floor(n);

    if (n == (n & ~(n - 1))) // zero or a power of two

        return floor;

    else

        return floor + 1;

}

int Bits::Log2Ceiling64(uint64 n) {

    int floor = Log2Floor64(n);

    if (n == (n & ~(n - 1))) // zero or a power of two

        return floor;

    else

        return floor + 1;

}

int Bits::FindLSBSetNonZero_Portable(uint32 n) {

    int rc = 31;

    for (int i = 4, shift = 1 << 4; i >= 0; --i) {

        const uint32 x = n << shift;

        if (x != 0) {

            n = x;

            rc -= shift;

        }

        shift >>= 1;

    }

    return rc;

}