The IBP interface consists of the Program View, Branch Predictor View and Accuracy View.

Program syntax and semantics are described in the Program Language section below. The Program View displays editable program text and highlights the next statement to be executed. The "Compile" button checks the validity of the program and enables execution.

The Branch Predictor View displays the current iteration and the state of the branch predictor.

• The "Step" button executes a statement and advances to the next statement or iteration.
• The "Run" button runs the specified number of iterations.
• The "Reset" button resets the current iteration and the state of the branch predictor.
• The "Update" button changes the parameters of the predictor as specified and resets its state.

The Predictor View displays the current predictor table as selected by the shift register and highlights the corresponding table entry if the next statement is a conditional branch (if), as well as the current PC and the result of the last prediction. The PC of each statement is its line number displayed in the editor.

The Accuracy view displays the accuracy of the branch predictor. The "Reset" button resets the accuracy and the count of branches/predictions.

The IBP Program Language is syntactically and semantically very similar to C:

let a = 1;
if (a < 2) {
  let b = rand(12);
  let c = b << 2;
  if (c > b) {}
}

A single program is a list of statements. Statements can be of two forms:

1. let <identifier> = <expression>;
   "Let" statements bind the identifier to the result of the expression within the current scope. Identifiers must begin with an alphabet or underscore and be followed by zero or more alphabets, underscores or digits.


2. if (<expression>) { [<statement>] }
   "If" statements are the branches that are predicted. As in C, conditional expressions that evaluate to zero are treated as false and non-zero values are treated as true. The branch is considered taken when the condition is true and is not taken when the condition is false. The statements in the "body" of the if statement execute within a new scope that inherits the variables defined in its parent scope.

Expressions can be one of:

• Number literals: These are decimal integer literals, or hexadecimal, octal or binary integer literals prefixed with 0x, 0o and 0b respectively.
• Variables: These are identifiers that are bound to a value in the current scope or a parent scope. The variable i is defined implicitly and is the loop counter.
• Unary or binary operations: These operate on one or two expressions respectively. The IBP Program Language has the same set of operators as C and C++ with the same precedence, with the exception of the ternary (?:), assignment (+=, -=, *= etc.) and increment/decrement (++, --) operators.
• Random numbers: The built-in rand(n) "function" produces a random integer between zero and n (inclusive) where n is any expression.

Notably, every expression evaluates to a number. This is a JavaScript number and not an integer, which means division is not floored: 1 / 2 is 0.5 and not 0.

The entire language is specified in this PEG file.