Intermediate C++ Game Programming Tutorial 23

Bit twiddling is a lot of bullshit that is usually avoided when possible because it leads to ass code. Still, it is necessary in various situations, so you gotta learn this shit, and now is as good a time as any I guess.

Topics Covered

• Bitwise AND (&), OR (|), and shift left/right (>> and <<)
• Unary bitwise NOT/complement (~) and bitwise XOR (^)
• Masking with & and combining with |
• Packing and unpacking smaller data in larger types
• Bit flags
• Bitwise arithmetic optimizations

Video Timestamp Index

Tutorial 23

• Introduce std::string ToBin(unsigned int n, int min_digits=0); to convert integers to their binary representation 0:15
• Bitwise operators 1:50
  • Biswise AND (&): 1010 & 1100 = 1000, also called a mask
  • Biswise OR (|): 1010 | 1100 = 1110, also called a mash
• Shifting operations 5:10
  • Shift left (<<): 0011 << 1 = 0110, shifts binary zeros in from the right side into the lower order bit position
  • Shift right (>>): 0110 >> 2 = 0001, shifts binary zeros in from the left side into the highter order bit position
  • EXCEPT: (-1)>>n, 1111>>2 = 1111, shifts binary ones in from the left
• Packing data 7:07
  • Example: combining four 8-bit numbers into one 32-bit number by using << and |

Homework

• Figure out how the binary string formatter routine works
• Figure out why x % 16 compiles to x & 0xF

The solution for the problems will not have its own video. Feel free to come on the discord and compare your answers with others, or to ask specific questions if you are having trouble understanding.

See also

• Next in series (Tutorial 24)
• Intermediate C++ Game Programming Series