Small Guide to MiniSAT

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Small Guide to MiniSAT

• Daniel Kroening
• ETH Zürich

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Overview MiniSat

• Winner of 2005 SAT competition
• Written by two PhD students
• Available athttp//www.cs.chalmers.se/Cs/Research
  /FormalMethods/MiniSat/Main.html
• Written in C
• Only 1954 lines!
• There is also a C version

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Niklas Eén
Niklas Sörensson
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Classes
Solver
GClause
VarOrder
Clause
Heap
Vec
Lit
uses
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Class vec

• Re-implementation of STL stdvector
• There is even a version that uses the STL instead
  of vec

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Class Lit

• Obvious implementation of the idea of a literal
• Variable sign is stored as one integer
• Sign is the least significant bit
• Variable number is the rest
• Several methods to convert/from to Lit

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Class Clause

• Stores clauses
• from original problem
• that are learnt
• Array of Lit
• Integer that encodes
• size of array
• bit whether original clause or learnt one
• Learnt clauses also have an activity value

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Class GClause

• Stores either
• a pointer to a clause
• a literal
• Least significant bit of pointerdistinguishes
  both
• Bit is 1 Literal, rest is the integer from Lit
• Bit is 0 pointer to clause
• Assumption malloc produces pointers with least
  significant bit 0

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Class VarOrder

• Heuristic for picking the next variable to make a
  decision on
• Uses Heap to build a priority queue
• Various activity measures

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Class Solver

• About 700 lines
• Stores
• the problem clauses
• the learnt clauses
• current assignment
• watched literals
• assignment stack
• Methods for
• Creating variables and clauses
• Removing clauses

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Class Solver

• Main method solve()
• Actual DPLL search()
• Unit clause propagation propagate()
• Conflict analysis analyze()
• Removal of learnt clauses reduceDB()