projects / unix-history / blame
| Commit | Line | Data |
|---|---|---|
| d503ec6c BJ |
1 | /* Copyright (c) 1979 Regents of the University of California */ |
| 2 | # | |
| 3 | /* | |
| 4 | * pxp - Pascal execution profiler | |
| 5 | * | |
| 6 | * Bill Joy UCB | |
| 7 | * Version 1.2 January 1979 | |
| 8 | */ | |
| 9 | ||
| 10 | #include "0.h" | |
| 11 | #include "tree.h" | |
| 12 | ||
| 13 | extern int *spacep; | |
| 14 | ||
| 15 | /* | |
| 16 | * LIST MANIPULATION ROUTINES | |
| 17 | * | |
| 18 | * The grammar for Pascal is written left recursively. | |
| 19 | * Because of this, the portions of parse trees which are to resemble | |
| 20 | * lists are in the somewhat inconvenient position of having | |
| 21 | * the nodes built from left to right, while we want to eventually | |
| 22 | * have as semantic value the leftmost node. | |
| 23 | * We could carry the leftmost node as semantic value, but this | |
| 24 | * would be inefficient as to add a new node to the list we would | |
| 25 | * have to chase down to the end. Other solutions involving a head | |
| 26 | * and tail pointer waste space. | |
| 27 | * | |
| 28 | * The simple solution to this apparent dilemma is to carry along | |
| 29 | * a pointer to the leftmost node in a list in the rightmost node | |
| 30 | * which is the current semantic value of the list. | |
| 31 | * When we have completed building the list, we can retrieve this | |
| 32 | * left end pointer very easily; neither adding new elements to the list | |
| 33 | * nor finding the left end is thus expensive. As the bottommost node | |
| 34 | * has an unused next pointer in it, no space is wasted either. | |
| 35 | * | |
| 36 | * The nodes referred to here are of the T_LISTPP type and have | |
| 37 | * the form: | |
| 38 | * | |
| 39 | * T_LISTPP some_pointer next_element | |
| 40 | * | |
| 41 | * Here some_pointer points to the things of interest in the list, | |
| 42 | * and next_element to the next thing in the list except for the | |
| 43 | * rightmost node, in which case it points to the leftmost node. | |
| 44 | * The next_element of the rightmost node is of course zapped to the | |
| 45 | * NIL pointer when the list is completed. | |
| 46 | * | |
| 47 | * Thinking of the lists as tree we heceforth refer to the leftmost | |
| 48 | * node as the "top", and the rightmost node as the "bottom" or as | |
| 49 | * the "virtual root". | |
| 50 | */ | |
| 51 | \f | |
| 52 | /* | |
| 53 | * Make a new list | |
| 54 | */ | |
| 55 | newlist(new) | |
| 56 | register int *new; | |
| 57 | { | |
| 58 | ||
| 59 | if (new == NIL) | |
| 60 | return (NIL); | |
| 61 | return (tree3(T_LISTPP, new, spacep)); | |
| 62 | } | |
| 63 | ||
| 64 | /* | |
| 65 | * Add a new element to an existing list | |
| 66 | */ | |
| 67 | addlist(vroot, new) | |
| 68 | register int *vroot; | |
| 69 | int *new; | |
| 70 | { | |
| 71 | register int *top; | |
| 72 | ||
| 73 | if (new == NIL) | |
| 74 | return (vroot); | |
| 75 | if (vroot == NIL) | |
| 76 | return (newlist(new)); | |
| 77 | top = vroot[2]; | |
| 78 | vroot[2] = spacep; | |
| 79 | return (tree3(T_LISTPP, new, top)); | |
| 80 | } | |
| 81 | ||
| 82 | /* | |
| 83 | * Fix up the list which has virtual root vroot. | |
| 84 | * We grab the top pointer and return it, zapping the spot | |
| 85 | * where it was so that the tree is not circular. | |
| 86 | */ | |
| 87 | fixlist(vroot) | |
| 88 | register int *vroot; | |
| 89 | { | |
| 90 | register int *top; | |
| 91 | ||
| 92 | if (vroot == NIL) | |
| 93 | return (NIL); | |
| 94 | top = vroot[2]; | |
| 95 | vroot[2] = NIL; | |
| 96 | return (top); | |
| 97 | } | |
| 98 | \f | |
| 99 | ||
| 100 | /* | |
| 101 | * Set up a T_VAR node for a qualified variable. | |
| 102 | * Init is the initial entry in the qualification, | |
| 103 | * or NIL if there is none. | |
| 104 | */ | |
| 105 | setupvar(var, init) | |
| 106 | char *var; | |
| 107 | register int *init; | |
| 108 | { | |
| 109 | ||
| 110 | if (init != NIL) | |
| 111 | init = newlist(init); | |
| 112 | return (tree4(T_VAR, NOCON, var, init)); | |
| 113 | } |