--------------------------------------------------------------------------------- -- | -- Module : Data.SBV -- Copyright : (c) Levent Erkok -- License : BSD3 -- Maintainer : erkokl@gmail.com -- Stability : experimental -- Portability : portable -- -- (The sbv library is hosted at <http://github.com/LeventErkok/sbv>. -- Comments, bug reports, and patches are always welcome.) -- -- SBV: Symbolic Bit Vectors in Haskell -- -- Express properties about bit-precise Haskell programs and automatically prove -- them using SMT solvers. -- -- >>> prove $ \x -> x `shiftL` 2 .== 4 * (x :: SWord8) -- Q.E.D. -- -- >>> prove $ forAll ["x"] $ \x -> x `shiftL` 2 .== (x :: SWord8) -- Falsifiable. Counter-example: -- x = 128 :: SWord8 -- -- The function 'prove' has the following type: -- -- @ -- 'prove' :: 'Provable' a => a -> 'IO' 'ThmResult' -- @ -- -- The class 'Provable' comes with instances for n-ary predicates, for arbitrary n. -- The predicates are just regular Haskell functions over symbolic signed and unsigned -- bit-vectors. Functions for checking satisfiability ('sat' and 'allSat') are also -- provided. -- -- In particular, the sbv library introduces the types: -- -- * 'SBool': Symbolic Booleans (bits) -- -- * 'SWord8', 'SWord16', 'SWord32', 'SWord64': Symbolic Words (unsigned) -- -- * 'SInt8', 'SInt16', 'SInt32', 'SInt64': Symbolic Ints (signed) -- -- * 'SArray', 'SFunArray': Flat arrays of symbolic values -- -- * Symbolic polynomials over GF(2^n), polynomial arithmetic, and CRCs -- -- * Uninterpreted constants and functions over symbolic values, with user -- defined SMT-Lib axioms -- -- The user can construct ordinary Haskell programs using these types, which behave -- very similar to their concrete counterparts. In particular these types belong to the -- standard classes 'Num', 'Bits', custom versions of 'Eq' ('EqSymbolic') -- and 'Ord' ('OrdSymbolic'), along with several other custom classes for simplifying -- bit-precise programming with symbolic values. The framework takes full advantage -- of Haskell's type inference to avoid many common mistakes. -- -- Furthermore, predicates (i.e., functions that return 'SBool') built out of -- these types can also be: -- -- * proven correct via an external SMT solver (the 'prove' function) -- -- * checked for satisfiability (the 'sat', 'allSat' functions) -- -- * used in synthesis (the `sat` function with existentials) -- -- * quick-checked -- -- If a predicate is not valid, 'prove' will return a counterexample: An -- assignment to inputs such that the predicate fails. The 'sat' function will -- return a satisfying assignment, if there is one. The 'allSat' function returns -- all satisfying assignments, lazily. -- -- The sbv library uses third-party SMT solvers via the standard SMT-Lib interface: -- <http://goedel.cs.uiowa.edu/smtlib/>. -- -- The SBV library is designed to work with any SMT-Lib compliant SMT-solver. -- Currently, we support the Yices SMT solver from SRI: <http://yices.csl.sri.com/>, -- and the Z3 SMT solver from Microsoft: <http://research.microsoft.com/en-us/um/redmond/projects/z3/>. -- -- You /should/ download and install Yices on your machine, and make sure the -- @yices@ executable is in your path before using the sbv library, as it is the -- current default solver. Alternatively, you can specify the location of yices -- executable in the environment variable @SBV_YICES@ and the options to yices -- in @SBV_YICES_OPTIONS@. -- -- Use of quantified variables require an installation of z3. Again, -- z3 must be in your path. Or, you can use the @SBV_Z3@ and @SBV_Z3_OPTIONS@ -- environment variables to set the executable and the options. --------------------------------------------------------------------------------- module Data.SBV ( -- * Programming with symbolic values -- $progIntro -- ** Symbolic types -- *** Symbolic bit SBool -- *** Unsigned symbolic bit-vectors , SWord8, SWord16, SWord32, SWord64 -- *** Signed symbolic bit-vectors , SInt8, SInt16, SInt32, SInt64 -- *** Signed unbounded integers -- $unboundedLimitations , SInteger -- *** Abstract SBV type , SBV -- *** Arrays of symbolic values , SymArray(..), SArray, SFunArray, mkSFunArray -- *** Full binary trees , STree, readSTree, writeSTree, mkSTree -- ** Operations on symbolic words -- *** Word level , bitValue, setBitTo, oneIf, lsb, msb -- *** List level , allEqual, allDifferent -- *** Blasting/Unblasting , blastBE, blastLE, FromBits(..) -- *** Splitting, joining, and extending , Splittable(..) -- *** Sign-casting , SignCast(..) -- ** Polynomial arithmetic and CRCs , Polynomial(..), crcBV, crc -- ** Conditionals: Mergeable values , Mergeable(..) -- ** Symbolic equality , EqSymbolic(..) -- ** Symbolic ordering , OrdSymbolic(..) -- ** Division , BVDivisible(..) -- ** The Boolean class , Boolean(..) -- *** Generalizations of boolean operations , bAnd, bOr, bAny, bAll -- ** Pretty-printing and reading numbers in Hex & Binary , PrettyNum(..), readBin -- * Uninterpreted constants and functions , Uninterpreted(..) -- ** Accessing the handle , SBVUF, sbvUFName -- ** Adding axioms , addAxiom -- * Properties, proofs, and satisfiability -- $proveIntro -- ** Predicates , Predicate, Provable(..), Equality(..) -- ** Proving properties , prove, proveWith, isTheorem, isTheoremWithin -- ** Checking satisfiability , sat, satWith, isSatisfiable, isSatisfiableWithin -- ** Finding all satisfying assignments , allSat, allSatWith, numberOfModels -- ** Adding constraints -- $constrainIntro , constrain, pConstrain -- ** Checking constraint vacuity , isVacuous, isVacuousWith -- * Optimization -- $optimizeIntro , minimize, maximize, optimize , minimizeWith, maximizeWith, optimizeWith -- * Model extraction -- $modelExtraction -- ** Inspecting proof results -- $resultTypes , ThmResult(..), SatResult(..), AllSatResult(..), SMTResult(..) -- ** Programmable model extraction -- $programmableExtraction , SatModel(..), Modelable(..), displayModels -- * SMT Interface: Configurations and solvers , SMTConfig(..), OptimizeOpts(..), SMTSolver(..), yices, z3, defaultSMTCfg -- * Symbolic computations , Symbolic, output, SymWord(..) -- * Getting SMT-Lib output (for offline analysis) , compileToSMTLib -- * Test case generation , genTest, CW(..), Size(..) -- * Code generation from symbolic programs -- $cCodeGeneration , SBVCodeGen -- ** Setting code-generation options , cgPerformRTCs, cgSetDriverValues, cgGenerateDriver -- ** Designating inputs , cgInput, cgInputArr -- ** Designating outputs , cgOutput, cgOutputArr -- ** Designating return values , cgReturn, cgReturnArr -- ** Code generation with uninterpreted functions , cgAddPrototype, cgAddDecl, cgAddLDFlags, cgIntegerSize -- ** Compilation to C , compileToC, compileToCLib -- * Module exports -- $moduleExportIntro , module Data.Bits , module Data.Word , module Data.Int ) where import Data.SBV.BitVectors.Data import Data.SBV.BitVectors.GenTest import Data.SBV.BitVectors.Model import Data.SBV.BitVectors.Optimize import Data.SBV.BitVectors.PrettyNum import Data.SBV.BitVectors.Polynomial import Data.SBV.BitVectors.SignCast import Data.SBV.BitVectors.Splittable import Data.SBV.BitVectors.STree import Data.SBV.Compilers.C import Data.SBV.Compilers.CodeGen import Data.SBV.Provers.Prover import Data.SBV.Utils.Boolean import Data.Bits import Data.Word import Data.Int -- Haddock section documentation {- $progIntro The SBV library is really two things: * A framework for writing bit-precise programs in Haskell * A framework for proving properties of such programs using SMT solvers In this first section we will look at the constructs that will let us construct such programs in Haskell. The goal is to have a "seamless" experience, i.e., program in the usual Haskell style without distractions of symbolic coding. While Haskell helps in some aspects (the 'Num' and 'Bits' classes simplify coding), it makes life harder in others. For instance, @if-then-else@ only takes 'Bool' as a test in Haskell, and comparisons ('>' etc.) only return 'Bool's. Clearly we would like these values to be symbolic (i.e., 'SBool'), thus stopping us from using some native Haskell constructs. When symbolic versions of operators are needed, they are typically obtained by prepending a dot, for instance '==' becomes '.=='. Care has been taken to make the transition painless. In particular, any Haskell program you build out of symbolic components is fully concretely executable within Haskell, without the need for any custom interpreters. (They are truly Haskell programs, not AST's built out of pieces of syntax.) This provides for an integrated feel of the system, one of the original design goals for SBV. -} {- $proveIntro The SBV library provides a "push-button" verification system via automated SMT solving. The design goal is to let SMT solvers be used without any knowledge of how SMT solvers work or how different logics operate. The details are hidden behind the SBV framework, providing Haskell programmers with a clean API that is unencumbered by the details of individual solvers. To that end, we use the SMT-Lib standard (<http://goedel.cs.uiowa.edu/smtlib/>) to communicate with arbitrary SMT solvers. Unfortunately, the SMT-Lib version 1.X does not standardize how models are communicated back from solvers, so there is some work in parsing individual SMT solver output. The 2.X version of the SMT-Lib standard (not yet implemented by SMT solvers widely, unfortunately) will bring new standard features for getting models; at which time the SBV framework can be modified into a truly plug-and-play system where arbitrary SMT solvers can be used. -} {- $optimizeIntro Symbolic optimization. A call of the form: @minimize Quantified cost n valid@ returns @Just xs@, such that: * @xs@ has precisely @n@ elements * @valid xs@ holds * @cost xs@ is minimal. That is, for all sequences @ys@ that satisfy the first two criteria above, @cost xs .<= cost ys@ holds. If there is no such sequence, then 'minimize' will return 'Nothing'. The function 'maximize' is similar, except the comparator is '.>='. So the value returned has the largest cost (or value, in that case). The function 'optimize' allows the user to give a custom comparison function. The 'OptimizeOpts' argument controls how the optimization is done. If 'Quantified' is used, then the SBV optimization engine satisfies the following predicate: @exists xs. forall ys. valid xs && (valid ys ``implies`` (cost xs ``cmp`` cost ys))@ Note that this may cause efficiency problems as it involves alternating quantifiers. If 'OptimizeOpts' is set to 'Iterative' 'True', then SBV will programmatically search for an optimal solution, by repeatedly calling the solver appropriately. (The boolean argument controls whether progress reports are given. Use 'False' for quiet operation.) Note that the quantified and iterative versions are two different optimization approaches and may not necessarily yield the same results. In particular, the quantified version can find solutions where there is no global optimum value, while the iterative version would simply loop forever in such cases. On the other hand, the iterative version might be more suitable if the quantified version of the problem is too hard to deal with by the SMT solver. -} {- $modelExtraction The default 'Show' instances for prover calls provide all the counter-example information in a human-readable form and should be sufficient for most casual uses of sbv. However, tools built on top of sbv will inevitably need to look into the constructed models more deeply, programmatically extracting their results and performing actions based on them. The API provided in this section aims at simplifying this task. -} {- $resultTypes 'ThmResult', 'SatResult', and 'AllSatResult' are simple newtype wrappers over 'SMTResult'. Their main purpose is so that we can provide custom 'Show' instances to print results accordingly. -} {- $programmableExtraction While default 'Show' instances are sufficient for most use cases, it is sometimes desirable (especially for library construction) that the SMT-models are reinterpreted in terms of domain types. Programmable extraction allows getting arbitrarily typed models out of SMT models. -} {- $cCodeGeneration The SBV library can generate straight-line executable code in C. (While other target languages are certainly possible, currently only C is supported.) The generated code will perform no run-time memory-allocations, (no calls to @malloc@), so its memory usage can be predicted ahead of time. Also, the functions will execute precisely the same instructions in all calls, so they have predictable timing properties as well. The generated code has no loops or jumps, and is typically quite fast. While the generated code can be large due to complete unrolling, these characteristics make them suitable for use in hard real-time systems, as well as in traditional computing. -} {- $moduleExportIntro The SBV library exports the following modules wholesale, as user programs will have to import these three modules to make any sensible use of the SBV functionality. -} {- $unboundedLimitations The SBV library supports unbounded signed integers with the type 'SInteger', which are not subject to overflow/underflow as it is the case with the bounded types, such as 'SWord8', 'SInt16', etc. However, some bit-vector based operations are /not/ supported for the 'SInteger' type while in the verification mode. That is, you can use these operations on 'SInteger' values during normal programming/simulation. but the SMT translation will not support these operations since there corresponding operations are not supported in SMT-Lib. Note that this should rarely be a problem in practice, as these operations are mostly meaningful on fixed-size bit-vectors. The operations that are restricted to bounded word/int sizes are: * Rotations and shifts: 'rotateL', 'rotateR', 'shiftL', 'shiftR' * Bitwise logical ops: '.&.', '.|.', 'xor', 'complement' * Extraction and concatenation: 'split', '#', and 'extend' (see the 'Splittable' class) Usual arithmetic ('+', '-', '*', 'bvQuotRem') and logical operations ('.<', '.<=', '.>', '.>=', '.==', './=') operations are supported for 'SInteger' fully, both in programming and verification modes. -} {- $constrainIntro A constraint is a means for restricting the input domain of a formula. Here's a simple example: @ do x <- 'exists' \"x\" y <- 'exists' \"y\" 'constrain' $ x .> y 'constrain' $ x + y .>= 12 'constrain' $ y .>= 3 ... @ The first constraint requires @x@ to be larger than @y@. The scond one says that sum of @x@ and @y@ must be at least @12@, and the final one says that @y@ to be at least @3@. Constraints provide an easy way to assert additional properties on the input domain, right at the point of the introduction of variables. Note that the proper reading of a constraint depends on the context: * In a 'sat' (or 'allSat') call: The constraint added is asserted conjunctively. That is, the resulting satisfying model (if any) will always satisfy all the constraints given. * In a 'prove' call: In this case, the constraint acts as an implication. The property is proved under the assumption that the constraint holds. In other words, the constraint says that we only care about the input space that satisfies the constraint. * In a 'quickCheck' call: The constraint acts as a filter for 'quickCheck'; if the constraint does not hold, then the input value is considered to be irrelevant and is skipped. Note that this is similar to 'prove', but is stronger: We do not accept a test case to be valid just because the constraints fail on them, although semantically the implication does hold. We simply skip that test case as a /bad/ test vector. * In a 'genTest' call: Similar to 'quickCheck' and 'prove': If a constraint does not hold, the input value is ignored and is not included in the test set. A good use case (in fact the motivating use case) for 'constrain' is attaching a constraint to a 'forall' or 'exists' variable at the time of its creation. Also, the conjunctive semantics for 'sat' and the implicative semantics for 'prove' simplify programming by choosing the correct interpretation automatically. However, one should be aware of the semantic difference. For instance, in the presence of constraints, formulas that are /provable/ are not necessarily /satisfiable/. To wit, consider: @ do x <- 'exists' \"x\" 'constrain' $ x .< x return $ x .< (x :: 'SWord8') @ This predicate is unsatisfiable since no element of 'SWord8' is less than itself. But it's (vacuously) true, since it excludes the entire domain of values, thus making the proof trivial. Hence, this predicate is provable, but is not satisfiable. To make sure the given constraints are not vacuous, the functions 'isVacuous' (and 'isVacuousWith') can be used. Also note that this semantics imply that test case generation ('genTest') and quick-check can take arbitrarily long in the presence of constraints, if the random input values generated rarely satisfy the constraints. (As an extreme case, consider @'constrain' 'false'@.) A probabilistic constraint (see 'pConstrain') attaches a probability threshold for the constraint to be considered. For instance: @'pConstrain' 0.8 c@ will add the constraint @c@ 80% of the time. This variant is useful for 'genTest' and 'quickCheck' functions, where we want to filter the test cases according to some probability distribution, to make sure that the test-vectors are drawn from interesting subsets of the input space. Note that while 'constrain' can be used freely, 'pConstrain' is only allowed in the contexts of 'genTest' or 'quickCheck'. Calls to 'pConstrain' in a prove/sat call will be rejected as it makes no sense. Also, 'constrain' and 'pConstrain' calls during code-generation will also be rejected, for similar reasons. -} {-# ANN module "HLint: ignore Use import/export shortcut" #-}