BrainFuck part 4 - Advanced maths

Welcome!

Welcome to this new playground about the BF language. Make sure you already read

• Getting started with BrainFuck
• BrainFuck part 2 - Working with arrays
• BrainFuck part 3 - Write a BF interpreter in BF

playgrounds if you didn't already !

The goal of this playground is to play with maths a bit more. Let's start with something simple : read a number.

In all the previous playground steps, data were read as "chars", mapped to ASCII values, but what if we want to type 123 and have a value 123 (instead of 3 chars)?

Let's start

• Memory: 0, 0, 0, 0
• Cursor: on first cell
• Input: a decimal number

Process

• invariant : first cell is the actually read number
• Read next digit on second cell
• While a digit has been read
  • Convert char into digit (-48)
  • Multiply number of first cell by ten
  • Add second cell to first
    • More exactly : add first cell 9 times to the second (needs less extra memory)
    • then add second to first
• loop
• first cell : the decimal number

Code

>,                      read next digit on second cell
[                       while digit is read
  >++++++[-<-------->]  convert into digit
  >+++++++++[           do 9 times
    <<<[->+>+<<]        add first cell to second and create a save copy
    >>[-<<+>>]          put save copy back on first cell
  >-]                   loop (9 times)
  <<[-<+>],             add second to first then read next digit
]<                      loop

Minified version

>,[>++++++[-<-------->]>+++++++++[<<<[->+>+<<]>>[-<<+>>]>-]<<[-<+>],]<

Final state

• Memory: N, 0, 0, 0
• Cursor: on N
• Input: empty
• Output: unchanged

Test program

This very basic program reads ASCII code and prints it

>,[>++++++[-<-------->]>+++++++++[<  read number
<<[->+>+<<]>>[-<<+>>]>-]<<[-<+>],]<  ** part 2 **
.                                    print as ASCII code

Try with inputs from 65 to 90 for example to have all uppercased letters