zzt93/CSAPP

CSAPP

Resources about Computer System: A Programmer's Perspective

• some code solutions for problems in book
• book in pdf
• old editoin solution manual(in English)
• newer edition solution in Chinese(not completely same with book)
• my reading note

Tricks

Chapter 2

use 'flag' and | to replace if(){}else{}

/* 2.73 Addition that saturates to TMin or TMax
   Your function should follow the bit-level integer coding rules
 */
int saturating_add(int x, int y){
    int sum = x + y;
    int bits = sizeof x << 3;
    int xmsb = x >> (bits - 1)
        , ymsb = y >> (bits - 1)
        , smsb = sum >> (bits - 1);
    int p_o = !xmsb & !ymsb & smsb;
    int n_o = xmsb & ymsb & !smsb;
    int no_o = !p_o & !n_o;
    return (p_o & TMAX) | (n_o & TMIN) | (no_o & sum);
}

use >>, << to replace loop

/*
Return 1 when x contains an odd number of 1s; 0 otherwise.
Assume w=32.
GET:
1. xor keep 1's number still odd/even
2. bit manipulate can work like following recusive way.
*/
int odd_ones(unsigned x) {
    x = x ^ (x >> 16);
    x = x ^ (x >> 8);
    x = x ^ (x >> 4);
    x = x ^ (x >> 2);
    x = x ^ (x >> 1);
    return x;
}

test special case: INT_MIN, 0

characteristic of Integer: non-symetric, may overflow