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| 1 | /* Parse tree node implementation */ | ||
| 2 | |||
| 3 | #include "Python.h" | ||
| 4 | #include "node.h" | ||
| 5 | #include "errcode.h" | ||
| 6 | |||
| 7 | node * | ||
| 8 | PyNode_New(int type) | ||
| 9 | { | ||
| 10 | node *n = (node *) PyObject_MALLOC(1 * sizeof(node)); | ||
| 11 | if (n == NULL) | ||
| 12 | return NULL; | ||
| 13 | n->n_type = type; | ||
| 14 | n->n_str = NULL; | ||
| 15 | n->n_lineno = 0; | ||
| 16 | n->n_nchildren = 0; | ||
| 17 | n->n_child = NULL; | ||
| 18 | return n; | ||
| 19 | } | ||
| 20 | |||
| 21 | /* See comments at XXXROUNDUP below. Returns -1 on overflow. */ | ||
| 22 | static int | ||
| 23 | fancy_roundup(int n) | ||
| 24 | { | ||
| 25 | /* Round up to the closest power of 2 >= n. */ | ||
| 26 | int result = 256; | ||
| 27 | assert(n > 128); | ||
| 28 | while (result < n) { | ||
| 29 | result <<= 1; | ||
| 30 | if (result <= 0) | ||
| 31 | return -1; | ||
| 32 | } | ||
| 33 | return result; | ||
| 34 | } | ||
| 35 | |||
| 36 | /* A gimmick to make massive numbers of reallocs quicker. The result is | ||
| 37 | * a number >= the input. In PyNode_AddChild, it's used like so, when | ||
| 38 | * we're about to add child number current_size + 1: | ||
| 39 | * | ||
| 40 | * if XXXROUNDUP(current_size) < XXXROUNDUP(current_size + 1): | ||
| 41 | * allocate space for XXXROUNDUP(current_size + 1) total children | ||
| 42 | * else: | ||
| 43 | * we already have enough space | ||
| 44 | * | ||
| 45 | * Since a node starts out empty, we must have | ||
| 46 | * | ||
| 47 | * XXXROUNDUP(0) < XXXROUNDUP(1) | ||
| 48 | * | ||
| 49 | * so that we allocate space for the first child. One-child nodes are very | ||
| 50 | * common (presumably that would change if we used a more abstract form | ||
| 51 | * of syntax tree), so to avoid wasting memory it's desirable that | ||
| 52 | * XXXROUNDUP(1) == 1. That in turn forces XXXROUNDUP(0) == 0. | ||
| 53 | * | ||
| 54 | * Else for 2 <= n <= 128, we round up to the closest multiple of 4. Why 4? | ||
| 55 | * Rounding up to a multiple of an exact power of 2 is very efficient, and | ||
| 56 | * most nodes with more than one child have <= 4 kids. | ||
| 57 | * | ||
| 58 | * Else we call fancy_roundup() to grow proportionately to n. We've got an | ||
| 59 | * extreme case then (like test_longexp.py), and on many platforms doing | ||
| 60 | * anything less than proportional growth leads to exorbitant runtime | ||
| 61 | * (e.g., MacPython), or extreme fragmentation of user address space (e.g., | ||
| 62 | * Win98). | ||
| 63 | * | ||
| 64 | * In a run of compileall across the 2.3a0 Lib directory, Andrew MacIntyre | ||
| 65 | * reported that, with this scheme, 89% of PyObject_REALLOC calls in | ||
| 66 | * PyNode_AddChild passed 1 for the size, and 9% passed 4. So this usually | ||
| 67 | * wastes very little memory, but is very effective at sidestepping | ||
| 68 | * platform-realloc disasters on vulnerable platforms. | ||
| 69 | * | ||
| 70 | * Note that this would be straightforward if a node stored its current | ||
| 71 | * capacity. The code is tricky to avoid that. | ||
| 72 | */ | ||
| 73 | #define XXXROUNDUP(n) ((n) <= 1 ? (n) : \ | ||
| 74 | (n) <= 128 ? (((n) + 3) & ~3) : \ | ||
| 75 | fancy_roundup(n)) | ||
| 76 | |||
| 77 | |||
| 78 | int | ||
| 79 | PyNode_AddChild(register node *n1, int type, char *str, int lineno, int col_offset) | ||
| 80 | { | ||
| 81 | const int nch = n1->n_nchildren; | ||
| 82 | int current_capacity; | ||
| 83 | int required_capacity; | ||
| 84 | node *n; | ||
| 85 | |||
| 86 | if (nch == INT_MAX || nch < 0) | ||
| 87 | return E_OVERFLOW; | ||
| 88 | |||
| 89 | current_capacity = XXXROUNDUP(nch); | ||
| 90 | required_capacity = XXXROUNDUP(nch + 1); | ||
| 91 | if (current_capacity < 0 || required_capacity < 0) | ||
| 92 | return E_OVERFLOW; | ||
| 93 | if (current_capacity < required_capacity) { | ||
| 94 | n = n1->n_child; | ||
| 95 | n = (node *) PyObject_REALLOC(n, | ||
| 96 | required_capacity * sizeof(node)); | ||
| 97 | if (n == NULL) | ||
| 98 | return E_NOMEM; | ||
| 99 | n1->n_child = n; | ||
| 100 | } | ||
| 101 | |||
| 102 | n = &n1->n_child[n1->n_nchildren++]; | ||
| 103 | n->n_type = type; | ||
| 104 | n->n_str = str; | ||
| 105 | n->n_lineno = lineno; | ||
| 106 | n->n_col_offset = col_offset; | ||
| 107 | n->n_nchildren = 0; | ||
| 108 | n->n_child = NULL; | ||
| 109 | return 0; | ||
| 110 | } | ||
| 111 | |||
| 112 | /* Forward */ | ||
| 113 | static void freechildren(node *); | ||
| 114 | |||
| 115 | |||
| 116 | void | ||
| 117 | PyNode_Free(node *n) | ||
| 118 | { | ||
| 119 | if (n != NULL) { | ||
| 120 | freechildren(n); | ||
| 121 | PyObject_FREE(n); | ||
| 122 | } | ||
| 123 | } | ||
| 124 | |||
| 125 | static void | ||
| 126 | freechildren(node *n) | ||
| 127 | { | ||
| 128 | int i; | ||
| 129 | for (i = NCH(n); --i >= 0; ) | ||
| 130 | freechildren(CHILD(n, i)); | ||
| 131 | if (n->n_child != NULL) | ||
| 132 | PyObject_FREE(n->n_child); | ||
| 133 | if (STR(n) != NULL) | ||
| 134 | PyObject_FREE(STR(n)); | ||
| 135 | } | ||