bitvec-ii.fq

// This file showcases bitvector functions that in smtlib2 are
// indexed identifiers. This means that instead of writing
// (zero_extend 2 bv) to extend a bitvector by 2 bits, we
// write ((_ zero_extend 2) bv).

// You can see the '_' as kind of applying type level arguments.
// In the case of 'zero_extend', it determines the size of the
// output bitvector. 

// To emulate this in liquid fixpoint, we want the output to 
// match exactly the format of indexed identifiers of smtlib2. 
// This comes down to defining our own '_' and parenthesizing 
// the expression in LF exactly as we would in the smt format.

// The last trick here, is that we cannot apply a parenthesized
// expression to an expression. For this we have defined the 
// additional expression 'app', which simply applies its operands.
// 'app' is elaborated to the empty string to the SMT solver, such
// that (app (_ zero_extend 2) bv) becomes ( (_ zero_extend 2) bv).

bind 0 x : {v : (BitVec Size4) | v = (lit "#b1000" (BitVec Size4))}
bind 1 y : {v : (BitVec Size4) | v = (app (_ rotate_right 7) x)}
bind 2 z : {v : (BitVec Size4) | v = (lit "#b0001" (BitVec Size4))}

constraint:
  env [0;1;2]
  lhs {v : (BitVec Size4) | [ v = y ] }
  rhs {v : (BitVec Size4) | [ v = z ] }
  id 0 tag []

bind 3 y : {v : (BitVec Size6) | v = (app (_ zero_extend 2) x)}
bind 4 z : {v : (BitVec Size6) | v = (lit "#b001000" (BitVec Size6))}

constraint:
  env [0;3;4]
  lhs {v : (BitVec Size6) | [ v = y ] }
  rhs {v : (BitVec Size6) | [ v = z ] }
  id 1 tag []

bind 5 y : {v : (BitVec Size6) | v = (app (_ sign_extend 2) x)}
bind 6 z : {v : (BitVec Size6) | v = (lit "#b111000" (BitVec Size6))}

constraint:
  env [0;5;6]
  lhs {v : (BitVec Size6) | [ v = y ] }
  rhs {v : (BitVec Size6) | [ v = z ] }
  id 2 tag []

bind 7 y : {v : (BitVec Size8) | v = (app (_ repeat 2) x)}
bind 8 z : {v : (BitVec Size8) | v = (lit "#b10001000" (BitVec Size8))}

constraint:
  env [0;7;8]
  lhs {v : (BitVec Size8) | [ v = y ] }
  rhs {v : (BitVec Size8) | [ v = z ] }
  id 3 tag []

bind 9  y : {v : (BitVec Size2) | v = (app (_ extract 3 2) x)}
bind 10 z : {v : (BitVec Size2) | v = (lit "#b10" (BitVec Size2))}

constraint:
  env [0;9;10]
  lhs {v : (BitVec Size2) | [ v = y ] }
  rhs {v : (BitVec Size2) | [ v = z ] }
  id 4 tag []