# 2018q3 Homework5 (bits)

contributed by < [`dange0`](https://github.com/dange0) >

###### tags: `sysprog2018`

## 實做
### absVal

int absVal(int x)
{
    int y;
    y = x >> 31;

    return (x ^ y) - y;
}

### addOK

int addOK(int x, int y)
{
    unsigned int x_msb, y_msb, sum_msb;
    y_msb = (y >> 31);
    x_msb = (x >> 31);
    sum_msb = ((x + y) >> 31);
    return (((x_msb ^ y_msb) + ((~(x_msb ^ y_msb)) & (~(x_msb ^ sum_msb)))) &
            0x1);
}

### allEvenBits

int allEvenBits(int x)
{
    x &= x >> 2;
    x &= x >> 4;
    x &= x >> 8;
    x &= x >> 16;
    return (x & 0x1);
}

### allOddBits

int allOddBits(int x)
{
    x &= x >> 2;
    x &= x >> 4;
    x &= x >> 8;
    x &= x >> 16;
    return ((x >> 1) & 0x1);
}

### anyEvenBit

int anyEvenBit(int x)
{
    x |= x >> 2;
    x |= x >> 4;
    x |= x >> 8;
    x |= x >> 16;
    return (x & 0x1);
}

### anyOddBit

int anyOddBit(int x)
{
    x |= x >> 2;
    x |= x >> 4;
    x |= x >> 8;
    x |= x >> 16;
    return ((x >> 0x1) & 0x1);
}

### bang

int bang(int x)
{
    x |= x >> 1;
    x |= x >> 2;
    x |= x >> 4;
    x |= x >> 8;
    x |= x >> 16;
    return (~x & 0x1);
}

### bitAnd

int bitAnd(int x, int y)
{
    return ~(~x | ~y);
}

### bitCount

int bitCount(int x)
{
    int mask1 = 0x55;
    int mask2 = 0x33;
    int mask3 = 0x0F;
    int mask4 = 0xFF;
    int mask5 = 0xFF;
    mask1 |= mask1 << 8;
    mask1 |= mask1 << 16;
    mask2 |= mask2 << 8;
    mask2 |= mask2 << 16;
    mask3 |= mask3 << 8;
    mask3 |= mask3 << 16;
    mask4 |= mask4 << 16;
    mask5 |= mask5 << 8;
    x = (x & mask1) + ((x >> 1) & mask1);
    x = (x & mask2) + ((x >> 2) & mask2);
    x = (x & mask3) + ((x >> 4) & mask3);
    x = (x & mask4) + ((x >> 8) & mask4);
    x = (x & mask5) + ((x >> 16) & mask5);
    return (x & mask5);
}

0101 0101 0101 0101 0101 0101 0101 0101
0011 0011 0011 0011 0011 0011 0011 0011
0000 1111 0000 1111 0000 1111 0000 1111
0000 0000 1111 1111 0000 0000 1111 1111
0000 0000 0000 0000 1111 1111 1111 1111

### bitNor

int bitNor(int x, int y)
{
    return ~x & ~y;
}

### bitOr

int bitOr(int x, int y)
{
    return ~(~x & ~y);
}

### bitParity

int bitParity(int x)
{
    x ^= x >> 1;
    x ^= x >> 2;
    x ^= x >> 4;
    x ^= x >> 8;
    x ^= x >> 16;
    return x & 0x1;
}