csapp

CSAPP

2.27

int uadd_ok(unsigned x, unsigned y)
{
    unsigned result = x + y;
    return result >= x;
}

2.30

int tadd_ok(int x, int y)
{
    int sum = x + y;
    int neg_over = x < 0 && y < 0 && sum >= 0;
    int pos_over = x >= 0 && y >= 0 && sum < 0;
     
    return !neg_over && !pos_over;
}

2.39

-(x<

2.40

(x<<2) + (x<<1)
(x<<5) - x
(x<<1) - (x<<3)
(x<<6) - (x<<3) - x

2.41

less operator is better

2.42

return (x >> 4) + (x & 0xF) && (x >> 31);

2.43

M=31 N=8

2.44

A. -2147483648
B. 1
C. 0 49152 = 1100 0000 0000 0000
D. 1
E. -2147483648
F. 1
G. 1

2.47

BITS    E   E   2E  F   M   2E*M    V   DECIMAL
0 00 00 0   0   1   0/4 0/4 0/4 0   0.0
0 00 01 0   0   1   1/4 1/4 1/4 1/4 0.25
0 00 10 0   0   1   2/4 2/4 2/4 1/2 0.5
0 00 11 0   0   1   3/4 3/4 3/4 3/4 0.75
0 01 00 1   0   1   0/4 4/4 4/4 1   1.0
0 01 01 1   0   1   1/4 5/4 5/4 5/4 1.25
0 01 10 1   0   1   2/4 6/4 6/4 3/2 1.5
0 01 11 1   0   1   3/4 7/4 7/4 7/4 1.75
0 10 00 2   1   2   0/4 4/4 8/4 2   2.0
0 10 01 2   1   2   1/4 5/4 10/4    5/2 2.5
0 10 10 2   1   2   2/4 6/4 12/4    3   3.0
0 10 11 2   1   2   3/4 7/4 14/4    7/2 3.5
0 11 00 -   -   -   -   -   -   -   Infinity
0 11 01 -   -   -   -   -   -   -   NaN
0 11 10 -   -   -   -   -   -   -   NaN
0 11 11 -   -   -   -   -   -   -   NaN

2.58

int is_little_endian()
{
    int a = 0xFF;
    byte_pointer p = (byte_pointer) &a;
    if (*p & 0xFF)
    {
        return 1;
    }
    else{
        return 0;
    }
}

2.59

int getxy(int x,int y)
{
    int tempx = x & 0xFF;
    int tempy = y & (~0xFF);
    return tempx+tempy;
}

2.64

int any_even_one(unsigned x)
{
    for (int i = 0; i < sizeof(unsigned)*4; ++i)
    {
        int y = x >> (i*2+1);
        y = y & 1 ;
        if (y)
        {
            return 1;
        }
    }

    return 0;
}

2.65

int even_ones(unsigned x)
{
    int result = 0;
    for (int i = 0; i < sizeof(unsigned)*8; ++i)
    {
        int y = x >> i;
        y = y & 1 ;
        if (y)
        {
            result+=1;
        }
    }

    if (!(result%2))
    {
        return 1;
    }else{
        return 0;
    }
}

2.71

int xbyte(packed_t word, int bytenum) {
    return (word << (24 - (bytenum << 3))) >> (bytenum << 3);
}