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Program.cs
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Program.cs
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/*
* Created by SharpDevelop.
* User: hugoyu
* Date: 2018/6/11
* Time: 19:50
*
* To change this template use Tools | Options | Coding | Edit Standard Headers.
*/
using System;
namespace BitHack
{
class Program
{
static int multiply_2_power_n(int val, int n)
{
// val * (2 power n)
return val << n;
}
static int divide_2_power_n(int val, int n)
{
// val / (2 power n)
return val >> n;
}
static int get_bit(int val, int n)
{
// get val's n-th bit
return val & (1 << n);
}
static int set_bit(int val, int n)
{
// set val's n-th bit to 1
return val | (1 << n);
}
static int clear_bit(int val, int n)
{
// set val's n-th bit to 0
return val & (~(1 << n));
}
static int update_bit(int val, int n, int s)
{
// update val's n-th bit to s (s should be 1 or 0)
return (val & (~(1 << n))) | (s << n);
}
static int toggle_bit(int val, int n)
{
// toggle val's n-th bit
return val ^ (1 << n);
}
static int clear_bits_to_n(int val, int n)
{
// clear bits from top to n
return val & ((1 << n) - 1);
}
static int clear_bits_from_n_1(int val, int n)
{
// clear bits from n - 1 to 0
return val & (~((1 << n) - 1));
}
static int modulus_power_of_2(int val, int n)
{
// val % (2 power n)
return val & ((1 << n) - 1);
}
static bool is_even(int val)
{
// check whether val is even
return (val & 1) == 0;
}
static bool is_odd(int val)
{
// check whether val is odd
return (val & 1) == 1;
}
static int get_sign(int val)
{
// get val's sign
return (val >> 31) & 1;
// if >> is logic shift, we can omit & 1
//return val >> 31;
}
static bool is_negative(int val)
{
// check whether val is negative
// not so good ...
return (val >> 31) != 0;
}
static bool is_power_of_2(int val)
{
// check whether val is power of 2
//return (val & (val - 1)) == 0;
return ((val & (val - 1)) == 0) && (val != 0);
}
static int floor_power_of_2(int val)
{
// calc power of 2 which <= val
val |= (val >> 1);
val |= (val >> 2);
val |= (val >> 4);
val |= (val >> 8);
val |= (val >> 16);
return val - (val >> 1);
}
static int ceil_power_of_2(int val)
{
// calc power of 2 which >= val
val -= 1;
val |= (val >> 1);
val |= (val >> 2);
val |= (val >> 4);
val |= (val >> 8);
val |= (val >> 16);
val += 1;
return val;
}
static int closest_power_of_2(int val)
{
var ceil = ceil_power_of_2(val);
var floor = ceil >> 1; // var floor = floor_power_of_2(val);
return val - floor < ceil - val ? floor : ceil;
}
static int min(int a, int b)
{
var mask = (a - b) >> 31;
return (a & mask) | (b & ~mask);
}
static int max(int a, int b)
{
var mask = (a - b) >> 31;
return (b & mask) | (a & ~mask);
}
static int clamp(int val, int min_val, int max_val)
{
return min(max(val, min_val), max_val);
}
static void swap(ref int a, ref int b)
{
a ^= b;
b ^= a;
a ^= b;
}
static int abs(int v)
{
var mask = v >> 31;
return (v + mask) ^ mask;
}
static int if_c_then_a_else_b(int c, int a, int b)
{
// c <= 0 means false, > 0 means true
return ((-c >> 31) & (a ^ b)) ^ b;
}
static int if_c_then_a_else_0(int c, int a)
{
// c <= 0 means false, > 0 means true
return (-c >> 31) & a;
}
static uint revert_bits(uint val)
{
val = ((val & 0x55555555) << 1) | ((val & 0xAAAAAAAA) >> 1);
val = ((val & 0x33333333) << 2) | ((val & 0xCCCCCCCC) >> 2);
val = ((val & 0x0F0F0F0F) << 4) | ((val & 0xF0F0F0F0) >> 4);
val = ((val & 0x00FF00FF) << 8) | ((val & 0xFF00FF00) >> 8);
val = ((val & 0x0000FFFF) << 16) | ((val & 0xFFFF0000) >> 16);
return val;
}
static uint revert_bytes(uint val)
{
val = ((val & 0x00FF00FF) << 8) | ((val & 0xFF00FF00) >> 8);
val = ((val & 0x0000FFFF) << 16) | ((val & 0xFFFF0000) >> 16);
return val;
}
static void Print(object val)
{
Console.WriteLine(val);
}
static void PrintHex(object val)
{
Console.WriteLine("{0:x}", val);
}
public static void Main(string[] args)
{
Print(multiply_2_power_n(1, 1)); // 2
Print(divide_2_power_n(2, 1)); // 1
Print(get_bit(1, 0)); // 1
Print(set_bit(0, 0)); // 1
Print(clear_bit(1, 0)); // 0
Print(update_bit(1, 0, 0)); // 0
Print(update_bit(1, 0, 1)); // 1
Print(update_bit(1, 2, 1)); // 5
Print(toggle_bit(1, 2)); // 5
Print(toggle_bit(toggle_bit(1, 2), 2)); // 1
Print(clear_bits_to_n(1, 1)); // 1
Print(clear_bits_from_n_1(2, 1)); // 2
Print(modulus_power_of_2(7, 3)); // 7
Print(modulus_power_of_2(17, 3)); // 1
Print(modulus_power_of_2(32, 3)); // 0
Print(is_even(2)); // true
Print(is_odd(2)); // false
Print(get_sign(1)); // 0
Print(get_sign(-1)); // 1
Print(is_negative(1)); // false
Print(is_negative(-1)); // true
Print(is_power_of_2(2)); // true
Print(is_power_of_2(3)); // false
Print(is_power_of_2(0)); // false
Print(floor_power_of_2(17)); // 16
Print(ceil_power_of_2(17)); // 32
Print(floor_power_of_2(16)); // 16
Print(ceil_power_of_2(16)); // 16
Print(closest_power_of_2(16)); // 16
Print(closest_power_of_2(17)); // 16
Print(closest_power_of_2(31)); // 32
Print(min(13, 14)); // 13
Print(max(13, 14)); // 14
Print(max(13, 13)); // 13
Print(clamp(13, 1, 5)); // 5
Print(clamp(13, 15, 17)); // 15
Print(clamp(13, 1, 17)); // 13
int a = 13;
int b = 17;
swap(ref a, ref b);
Print(a + " " + b); // 17 13
Print(abs(13)); // 13
Print(abs(-13)); // 13
Print(if_c_then_a_else_b(0, 13, 17)); // 17
Print(if_c_then_a_else_b(-1, 13, 17)); // 17
Print(if_c_then_a_else_b(1, 13, 17)); // 13
Print(if_c_then_a_else_0(0, 13)); // 0
Print(if_c_then_a_else_0(-1, 13)); // 0
Print(if_c_then_a_else_0(1, 13)); // 13
PrintHex(revert_bits(0x12345678)); // 0x1e6a2c48
PrintHex(revert_bytes(0x12345678)); // 0x78563412
Console.Write("Press any key to continue . . . ");
Console.ReadKey(true);
}
}
}