| 1 | # |
| 2 | /* |
| 3 | * pxp - Pascal execution profiler |
| 4 | * |
| 5 | * Bill Joy UCB |
| 6 | * Version 1.0 August 1977 |
| 7 | */ |
| 8 | |
| 9 | #include "whoami" |
| 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 | * Fix a statement list. This is similar to the |
| 101 | * work in fixlist, but we must also get rid of the |
| 102 | * nodes T_IFX which are inserted by the parser so |
| 103 | * that we can detect ';' before else errors. |
| 104 | * These nodes are always gone already anyways, except |
| 105 | * possibly in the presence of errors. |
| 106 | */ |
| 107 | fixstlist(vroot) |
| 108 | register int *vroot; |
| 109 | { |
| 110 | register int *ifstat, *top; |
| 111 | |
| 112 | if (vroot == NIL) |
| 113 | return (NIL); |
| 114 | top = vroot[2]; |
| 115 | vroot[2] = NIL; |
| 116 | ifstat = vroot[1]; |
| 117 | if (ifstat[0] == T_IFX) |
| 118 | ifstat[0] == T_IFEL; |
| 119 | return (top); |
| 120 | } |
| 121 | |
| 122 | /* |
| 123 | * Set up a T_VAR node for a qualified variable. |
| 124 | * Init is the initial entry in the qualification, |
| 125 | * or NIL if there is none. |
| 126 | */ |
| 127 | setupvar(var, init) |
| 128 | char *var; |
| 129 | register int *init; |
| 130 | { |
| 131 | |
| 132 | if (init != NIL) |
| 133 | init = newlist(init); |
| 134 | return (tree4(T_VAR, NOCON, var, init)); |
| 135 | } |