BWM: A Concrete Machine for Graph Reduction

/* Pointer or */ int data:30; /* data */ } uword; } word; /* Word in the heap */ typedef struct { word ptrss4]; /* Four pointers (or whatever) */ } node; 11 Appendix A Instruction encoding The description is given in pseudo-C, where we assume that bit elds are packed in a suitable way. All addresses are assumed to be big word aligned thus having four lsb zeroes that need not be stored. typedef struct { bool shared:1; /* set shared bit */ argtype type:2; /* argument type */ union { unsigned int stackoffs:5; /* unsigned offset for stack */ signed int heapoffs:5; /* signed offset for heap */ specsource special:5; /* special source */ } uarg; } argspec; typedef struct { argspec args:884]; /* argument specifiers */ bool shortinstr:1; /* true if this a short instruction */ bool write:1; /* write build register to memory */ bool push:1; /* push build register to stack/pc */ bool startalu:1; /* latch alu operands */ int stackadj:4; /* amount to pop from stack */ } shortinstr; typedef struct { shortinstr instr; /* instruction */ union { word litss2]; /* literals */ shortinstr instr2; /* or second instruction */ } u; } instr; B Node layout /* Address encodings */ typedef int memaddr; /* Generic address */ typedef struct { int arity:5; /* arity of function */ bool constr:1; /* constr/addr flag */ union { memaddr address:23; /* address of function */ int constrno:23; /* constructor function number */ } ucode; } codepointer; /* pointer to code */ typedef struct { bool share:1; /* is node possibly shared? */ memaddr address:28; /* address of node */ } nodepointer; /* pointer to node */ typedef struct { bool code:1; /* code/node flag */ union { codepointer cptr:29; /* code or */ nodepointer nptr:29; /* node pointer */ } uptr; } pointer; /* pointer in heap and stack */ /* Node layout */ typedef struct { bool used:1; /* Word used/unused flag */ bool ptr:1; /* Pointer/data flag */ union {