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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 | +} | |