bitrepl is a REPL / interpreter that aims to help students working with "bit twiddling hacks." Most C operators are supported (arithmetic and bitwise) as well as variable assignments. Numbers could be entered in decimal or hexadecimal.

$ git clone https://github.com/cuong-dang/bitrepl.git
$ cd bitrepl
$ make

• Unary: +, -, ~
• Arithmetic: +, -, *, /, %
• Bitwise: |, ^, &, <<, >>, >>>
• Assignment: =, |=, ^=, &=, <<=, >>=, >>>=, +=, -=, *=, /=, %=
• Comment: //

• Unary + and - are invalid for hexadecimal numbers.
• Left shift << by more than the current bit width returns 0.
• >>> is adopted from Java. It shifts right without sign extension.
• Variable names must consist of only letters and have at most 15 characters.
• Variables do not lose their set bits when the bit width is reduced; they will then be overflowed.

• set dm [bin|hex|dec]: Change output display mode to binary, hexadecimal, or decimal
• set bw x: Set bit width to x that must be positive, maximum 32, and divisible by 4
• help: Display help

Counting the number of bits set in v = 0xab

b> // an example bitrepl session counting the set bits of 0xab
b> 0xab
0000 0000 1010 1011
b> set bw 8
b> v = 0xab
1010 1011
b> v = (v & 0x55) + ((v >> 1) & 0x55)
0101 0110
b> v = (v & 0x33) + ((v >> 2) & 0x33)
0010 0011
b> v = (v & 0x0f) + ((v >> 4) & 0x0f)
0000 0101
b> set dm dec
d> v
5
d>

• (page) https://graphics.stanford.edu/~seander/bithacks.html
• (book) Hacker's Delight by Henry S. Warren