From 2e5030ada3cdf09db27905b55fb6086563ec73f4 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Dag-Erling=20Sm=C3=B8rgrav?= Date: Wed, 24 Jul 2024 18:17:08 +0200 Subject: [PATCH] Postpone position assignment until the end. During AST expansion, it is possible for new literal nodes to be created and given the same position as existing literals. The code attempts to reposition nodes when this happens but does not always succeed. The result is a short-circuit in the TNFA which can manifest as an infinite loop, e.g. a bounded iteration being treated as an unbounded one. This reshuffling can also leave positions unfilled, wasting memory. Instead of trying to assign positions to literal nodes on creation, and then having to renumber them on the fly during AST expansion, wait until the end and move position assignment into `tre_compute_nfl()`, which we rename to `tre_compute_npfl()`. --- lib/tre-ast.c | 4 +- lib/tre-ast.h | 2 +- lib/tre-compile.c | 106 ++++++++++++++++++++++------------------------ lib/tre-parse.c | 64 ++++++++++------------------ lib/tre-parse.h | 2 - 5 files changed, 75 insertions(+), 103 deletions(-) diff --git a/lib/tre-ast.c b/lib/tre-ast.c index acb387a..5a4bb19 100644 --- a/lib/tre-ast.c +++ b/lib/tre-ast.c @@ -33,7 +33,7 @@ tre_ast_new_node(tre_mem_t mem, tre_ast_type_t type, size_t size) } tre_ast_node_t * -tre_ast_new_literal(tre_mem_t mem, int code_min, int code_max, int position) +tre_ast_new_literal(tre_mem_t mem, int code_min, int code_max) { tre_ast_node_t *node; tre_literal_t *lit; @@ -44,7 +44,7 @@ tre_ast_new_literal(tre_mem_t mem, int code_min, int code_max, int position) lit = node->obj; lit->code_min = code_min; lit->code_max = code_max; - lit->position = position; + lit->position = -1; return node; } diff --git a/lib/tre-ast.h b/lib/tre-ast.h index d9af376..4f9589e 100644 --- a/lib/tre-ast.h +++ b/lib/tre-ast.h @@ -101,7 +101,7 @@ tre_ast_node_t * tre_ast_new_node(tre_mem_t mem, tre_ast_type_t type, size_t size); tre_ast_node_t * -tre_ast_new_literal(tre_mem_t mem, int code_min, int code_max, int position); +tre_ast_new_literal(tre_mem_t mem, int code_min, int code_max); tre_ast_node_t * tre_ast_new_iter(tre_mem_t mem, tre_ast_node_t *arg, int min, int max, diff --git a/lib/tre-compile.c b/lib/tre-compile.c index ebccfb8..b84399c 100644 --- a/lib/tre-compile.c +++ b/lib/tre-compile.c @@ -46,7 +46,7 @@ tre_add_tag_left(tre_mem_t mem, tre_ast_node_t *node, int tag_id) c = tre_mem_alloc(mem, sizeof(*c)); if (c == NULL) return REG_ESPACE; - c->left = tre_ast_new_literal(mem, TAG, tag_id, -1); + c->left = tre_ast_new_literal(mem, TAG, tag_id); if (c->left == NULL) return REG_ESPACE; c->right = tre_mem_alloc(mem, sizeof(tre_ast_node_t)); @@ -78,7 +78,7 @@ tre_add_tag_right(tre_mem_t mem, tre_ast_node_t *node, int tag_id) c = tre_mem_alloc(mem, sizeof(*c)); if (c == NULL) return REG_ESPACE; - c->right = tre_ast_new_literal(mem, TAG, tag_id, -1); + c->right = tre_ast_new_literal(mem, TAG, tag_id); if (c->right == NULL) return REG_ESPACE; c->left = tre_mem_alloc(mem, sizeof(tre_ast_node_t)); @@ -711,7 +711,7 @@ tre_copy_ast(tre_mem_t mem, tre_stack_t *stack, tre_ast_node_t *ast, tag_directions[max] = TRE_TAG_MAXIMIZE; first_tag = 0; } - *result = tre_ast_new_literal(mem, min, max, pos); + *result = tre_ast_new_literal(mem, min, max); if (*result == NULL) status = REG_ESPACE; @@ -798,8 +798,7 @@ typedef enum { iteration count to a catenated sequence of copies of the node. */ static reg_errcode_t tre_expand_ast(tre_mem_t mem, tre_stack_t *stack, tre_ast_node_t *ast, - int *position, tre_tag_direction_t *tag_directions, - int *max_depth) + tre_tag_direction_t *tag_directions, int *max_depth) { reg_errcode_t status = REG_OK; int bottom = tre_stack_num_objects(stack); @@ -949,7 +948,7 @@ tre_expand_ast(tre_mem_t mem, tre_stack_t *stack, tre_ast_node_t *ast, seq2 = copy; if (seq2 == NULL) return REG_ESPACE; - tmp = tre_ast_new_literal(mem, EMPTY, -1, -1); + tmp = tre_ast_new_literal(mem, EMPTY, -1); if (tmp == NULL) return REG_ESPACE; seq2 = tre_ast_new_union(mem, tmp, seq2); @@ -983,12 +982,12 @@ tre_expand_ast(tre_mem_t mem, tre_stack_t *stack, tre_ast_node_t *ast, tre_ast_node_t *tmp_l, *tmp_r, *tmp_node, *node_copy; int *old_params; - tmp_l = tre_ast_new_literal(mem, PARAMETER, 0, -1); + tmp_l = tre_ast_new_literal(mem, PARAMETER, 0); if (!tmp_l) return REG_ESPACE; ((tre_literal_t *)tmp_l->obj)->u.params = iter->params; iter->params[TRE_PARAM_DEPTH] = params_depth + 1; - tmp_r = tre_ast_new_literal(mem, PARAMETER, 0, -1); + tmp_r = tre_ast_new_literal(mem, PARAMETER, 0); if (!tmp_r) return REG_ESPACE; old_params = tre_mem_alloc(mem, sizeof(*old_params) @@ -1028,19 +1027,9 @@ tre_expand_ast(tre_mem_t mem, tre_stack_t *stack, tre_ast_node_t *ast, } } - *position += pos_add_total; - - /* `max_pos' should never be larger than `*position' if the above - code works, but just an extra safeguard let's make sure - `*position' is set large enough so enough memory will be - allocated for the transition table. */ - if (max_pos > *position) - *position = max_pos; - #ifdef TRE_DEBUG DPRINT(("Expanded AST:\n")); tre_ast_print(ast); - DPRINT(("*position %d, max_pos %d\n", *position, max_pos)); #endif return status; @@ -1305,33 +1294,36 @@ tre_match_empty(tre_stack_t *stack, tre_ast_node_t *node, int *tags, typedef enum { - NFL_RECURSE, - NFL_POST_UNION, - NFL_POST_CATENATION, - NFL_POST_ITERATION -} tre_nfl_stack_symbol_t; + NPFL_RECURSE, + NPFL_POST_UNION, + NPFL_POST_CATENATION, + NPFL_POST_ITERATION +} tre_npfl_stack_symbol_t; -/* Computes and fills in the fields `nullable', `firstpos', and `lastpos' for - the nodes of the AST `tree'. */ +/* Computes and fills in the fields `nullable', `position`, `firstpos', + and `lastpos' for the nodes of the AST `tree'; `nextpos' points to an + integer indicating the next available position, and will be updated on + return to reflect the number of additional positions assigned. */ static reg_errcode_t -tre_compute_nfl(tre_mem_t mem, tre_stack_t *stack, tre_ast_node_t *tree) +tre_compute_npfl(tre_mem_t mem, tre_stack_t *stack, tre_ast_node_t *tree, + int *nextpos) { int bottom = tre_stack_num_objects(stack); STACK_PUSHR(stack, voidptr, tree); - STACK_PUSHR(stack, int, NFL_RECURSE); + STACK_PUSHR(stack, int, NPFL_RECURSE); while (tre_stack_num_objects(stack) > bottom) { - tre_nfl_stack_symbol_t symbol; + tre_npfl_stack_symbol_t symbol; tre_ast_node_t *node; - symbol = (tre_nfl_stack_symbol_t)tre_stack_pop_int(stack); + symbol = (tre_npfl_stack_symbol_t)tre_stack_pop_int(stack); node = tre_stack_pop_voidptr(stack); switch (symbol) { - case NFL_RECURSE: + case NPFL_RECURSE: switch (node->type) { case LITERAL: @@ -1342,6 +1334,7 @@ tre_compute_nfl(tre_mem_t mem, tre_stack_t *stack, tre_ast_node_t *tree) /* Back references: nullable = false, firstpos = {i}, lastpos = {i}. */ node->nullable = 0; + lit->position = (*nextpos)++; node->firstpos = tre_set_one(mem, lit->position, 0, TRE_CHAR_MAX, 0, NULL, -1); if (!node->firstpos) @@ -1369,6 +1362,7 @@ tre_compute_nfl(tre_mem_t mem, tre_stack_t *stack, tre_ast_node_t *tree) /* Literal at position i: nullable = false, firstpos = {i}, lastpos = {i}. */ node->nullable = 0; + lit->position = (*nextpos)++; node->firstpos = tre_set_one(mem, lit->position, (int)lit->code_min, (int)lit->code_max, 0, NULL, -1); @@ -1389,36 +1383,36 @@ tre_compute_nfl(tre_mem_t mem, tre_stack_t *stack, tre_ast_node_t *tree) /* Compute the attributes for the two subtrees, and after that for this node. */ STACK_PUSHR(stack, voidptr, node); - STACK_PUSHR(stack, int, NFL_POST_UNION); + STACK_PUSHR(stack, int, NPFL_POST_UNION); STACK_PUSHR(stack, voidptr, ((tre_union_t *)node->obj)->right); - STACK_PUSHR(stack, int, NFL_RECURSE); + STACK_PUSHR(stack, int, NPFL_RECURSE); STACK_PUSHR(stack, voidptr, ((tre_union_t *)node->obj)->left); - STACK_PUSHR(stack, int, NFL_RECURSE); + STACK_PUSHR(stack, int, NPFL_RECURSE); break; case CATENATION: /* Compute the attributes for the two subtrees, and after that for this node. */ STACK_PUSHR(stack, voidptr, node); - STACK_PUSHR(stack, int, NFL_POST_CATENATION); + STACK_PUSHR(stack, int, NPFL_POST_CATENATION); STACK_PUSHR(stack, voidptr, ((tre_catenation_t *)node->obj)->right); - STACK_PUSHR(stack, int, NFL_RECURSE); + STACK_PUSHR(stack, int, NPFL_RECURSE); STACK_PUSHR(stack, voidptr, ((tre_catenation_t *)node->obj)->left); - STACK_PUSHR(stack, int, NFL_RECURSE); + STACK_PUSHR(stack, int, NPFL_RECURSE); break; case ITERATION: /* Compute the attributes for the subtree, and after that for this node. */ STACK_PUSHR(stack, voidptr, node); - STACK_PUSHR(stack, int, NFL_POST_ITERATION); + STACK_PUSHR(stack, int, NPFL_POST_ITERATION); STACK_PUSHR(stack, voidptr, ((tre_iteration_t *)node->obj)->arg); - STACK_PUSHR(stack, int, NFL_RECURSE); + STACK_PUSHR(stack, int, NPFL_RECURSE); break; } - break; /* end case: NFL_RECURSE */ + break; /* end case: NPFL_RECURSE */ - case NFL_POST_UNION: + case NPFL_POST_UNION: { tre_union_t *uni = (tre_union_t *)node->obj; node->nullable = uni->left->nullable || uni->right->nullable; @@ -1433,7 +1427,7 @@ tre_compute_nfl(tre_mem_t mem, tre_stack_t *stack, tre_ast_node_t *tree) break; } - case NFL_POST_ITERATION: + case NPFL_POST_ITERATION: { tre_iteration_t *iter = (tre_iteration_t *)node->obj; @@ -1446,7 +1440,7 @@ tre_compute_nfl(tre_mem_t mem, tre_stack_t *stack, tre_ast_node_t *tree) break; } - case NFL_POST_CATENATION: + case NPFL_POST_CATENATION: { int num_tags, *tags, assertions, params_seen; int *params; @@ -1839,7 +1833,6 @@ tre_ast_to_tnfa(tre_ast_node_t *node, tre_tnfa_transition_t *transitions, return errcode; } - #define ERROR_EXIT(err) \ do \ { \ @@ -1864,6 +1857,7 @@ tre_compile(regex_t *preg, const tre_char_t *regex, size_t n, int cflags) tre_tag_direction_t *tag_directions = NULL; reg_errcode_t errcode; tre_mem_t mem; + int numpos = 0; /* Parse context. */ tre_parse_ctx_t parse_ctx; @@ -1970,8 +1964,8 @@ tre_compile(regex_t *preg, const tre_char_t *regex, size_t n, int cflags) } /* Expand iteration nodes. */ - errcode = tre_expand_ast(mem, stack, tree, &parse_ctx.position, - tag_directions, &tnfa->params_depth); + errcode = tre_expand_ast(mem, stack, tree, tag_directions, + &tnfa->params_depth); if (errcode != REG_OK) ERROR_EXIT(errcode); @@ -1980,7 +1974,7 @@ tre_compile(regex_t *preg, const tre_char_t *regex, size_t n, int cflags) for example "a*" or "ab*". Figure out a simple way to detect this possibility. */ tmp_ast_l = tree; - tmp_ast_r = tre_ast_new_literal(mem, 0, 0, parse_ctx.position++); + tmp_ast_r = tre_ast_new_literal(mem, 0, 0); if (tmp_ast_r == NULL) ERROR_EXIT(REG_ESPACE); @@ -1988,29 +1982,29 @@ tre_compile(regex_t *preg, const tre_char_t *regex, size_t n, int cflags) if (tree == NULL) ERROR_EXIT(REG_ESPACE); + errcode = tre_compute_npfl(mem, stack, tree, &numpos); + if (errcode != REG_OK) + ERROR_EXIT(errcode); + #ifdef TRE_DEBUG tre_ast_print(tree); - DPRINT(("Number of states: %d\n", parse_ctx.position)); + DPRINT(("Number of states: %d\n", numpos)); #endif /* TRE_DEBUG */ - errcode = tre_compute_nfl(mem, stack, tree); - if (errcode != REG_OK) - ERROR_EXIT(errcode); - - counts = xmalloc(sizeof(int) * parse_ctx.position); + counts = xmalloc(sizeof(int) * numpos); if (counts == NULL) ERROR_EXIT(REG_ESPACE); - offs = xmalloc(sizeof(int) * parse_ctx.position); + offs = xmalloc(sizeof(int) * numpos); if (offs == NULL) ERROR_EXIT(REG_ESPACE); - for (i = 0; i < parse_ctx.position; i++) + for (i = 0; i < numpos; i++) counts[i] = 0; tre_ast_to_tnfa(tree, NULL, counts, NULL); add = 0; - for (i = 0; i < parse_ctx.position; i++) + for (i = 0; i < numpos; i++) { offs[i] = add; add += counts[i] + 1; @@ -2148,7 +2142,7 @@ tre_compile(regex_t *preg, const tre_char_t *regex, size_t n, int cflags) tnfa->num_transitions = add; tnfa->final = transitions + offs[tree->lastpos[0].position]; - tnfa->num_states = parse_ctx.position; + tnfa->num_states = numpos; tnfa->cflags = cflags; DPRINT(("final state %p\n", (void *)tnfa->final)); diff --git a/lib/tre-parse.c b/lib/tre-parse.c index b62c022..d0540cd 100644 --- a/lib/tre-parse.c +++ b/lib/tre-parse.c @@ -113,7 +113,7 @@ tre_new_item(tre_mem_t mem, int min, int max, int *i, int *max_i, return REG_ESPACE; *items = array = new_items; } - array[*i] = tre_ast_new_literal(mem, min, max, -1); + array[*i] = tre_ast_new_literal(mem, min, max); status = array[*i] == NULL ? REG_ESPACE : REG_OK; (*i)++; return status; @@ -491,7 +491,6 @@ tre_parse_bracket(tre_parse_ctx_t *ctx, tre_ast_node_t **result) { int k; DPRINT(("creating %d - %d\n", (int)l->code_min, (int)l->code_max)); - l->position = ctx->position; if (num_neg_classes > 0) { l->neg_classes = tre_mem_alloc(ctx->mem, @@ -527,7 +526,7 @@ tre_parse_bracket(tre_parse_ctx_t *ctx, tre_ast_node_t **result) { int k; DPRINT(("final: creating %d - %d\n", curr_min, (int)TRE_CHAR_MAX)); - n = tre_ast_new_literal(ctx->mem, curr_min, TRE_CHAR_MAX, ctx->position); + n = tre_ast_new_literal(ctx->mem, curr_min, TRE_CHAR_MAX); if (n == NULL) status = REG_ESPACE; else @@ -570,7 +569,6 @@ tre_parse_bracket(tre_parse_ctx_t *ctx, tre_ast_node_t **result) parse_bracket_done: xfree(items); - ctx->position++; *result = node; return status; } @@ -844,7 +842,7 @@ tre_parse_bound(tre_parse_ctx_t *ctx, tre_ast_node_t **result) /* Create the AST node(s). */ if (min == 0 && max == 0) { - *result = tre_ast_new_literal(ctx->mem, EMPTY, -1, -1); + *result = tre_ast_new_literal(ctx->mem, EMPTY, -1); if (*result == NULL) return REG_ESPACE; } @@ -1363,7 +1361,7 @@ tre_parse(tre_parse_ctx_t *ctx) subexpression was closed. POSIX leaves the meaning of this to be implementation-defined. We interpret this as an empty expression (which matches an empty string). */ - result = tre_ast_new_literal(ctx->mem, EMPTY, -1, -1); + result = tre_ast_new_literal(ctx->mem, EMPTY, -1); if (result == NULL) return REG_ESPACE; if (!(ctx->cflags & REG_EXTENDED)) @@ -1411,7 +1409,6 @@ tre_parse(tre_parse_ctx_t *ctx) if (status != REG_OK) return status; ctx->re += 2; - ctx->position = subctx.position; result = subctx.result; break; } @@ -1440,22 +1437,22 @@ tre_parse(tre_parse_ctx_t *ctx) { case L'b': result = tre_ast_new_literal(ctx->mem, ASSERTION, - ASSERT_AT_WB, -1); + ASSERT_AT_WB); ctx->re++; break; case L'B': result = tre_ast_new_literal(ctx->mem, ASSERTION, - ASSERT_AT_WB_NEG, -1); + ASSERT_AT_WB_NEG); ctx->re++; break; case L'<': result = tre_ast_new_literal(ctx->mem, ASSERTION, - ASSERT_AT_BOW, -1); + ASSERT_AT_BOW); ctx->re++; break; case L'>': result = tre_ast_new_literal(ctx->mem, ASSERTION, - ASSERT_AT_EOW, -1); + ASSERT_AT_EOW); ctx->re++; break; case L'x': @@ -1479,9 +1476,7 @@ tre_parse(tre_parse_ctx_t *ctx) ctx->re++; } val = strtol(tmp, NULL, 16); - result = tre_ast_new_literal(ctx->mem, (int)val, - (int)val, ctx->position); - ctx->position++; + result = tre_ast_new_literal(ctx->mem, (int)val, (int)val); break; } else if (ctx->re < ctx->re_end) @@ -1507,9 +1502,7 @@ tre_parse(tre_parse_ctx_t *ctx) ctx->re++; tmp[i] = 0; val = strtol(tmp, NULL, 16); - result = tre_ast_new_literal(ctx->mem, (int)val, (int)val, - ctx->position); - ctx->position++; + result = tre_ast_new_literal(ctx->mem, (int)val, (int)val); break; } /*FALLTHROUGH*/ @@ -1521,11 +1514,9 @@ tre_parse(tre_parse_ctx_t *ctx) int val = *ctx->re - L'0'; DPRINT(("tre_parse: backref: '%.*" STRF "'\n", REST(ctx->re - 1))); - result = tre_ast_new_literal(ctx->mem, BACKREF, val, - ctx->position); + result = tre_ast_new_literal(ctx->mem, BACKREF, val); if (result == NULL) return REG_ESPACE; - ctx->position++; ctx->max_backref = MAX(val, ctx->max_backref); ctx->re++; } @@ -1534,9 +1525,7 @@ tre_parse(tre_parse_ctx_t *ctx) /* Escaped character. */ DPRINT(("tre_parse: escaped: '%.*" STRF "'\n", REST(ctx->re - 1))); - result = tre_ast_new_literal(ctx->mem, *ctx->re, *ctx->re, - ctx->position); - ctx->position++; + result = tre_ast_new_literal(ctx->mem, *ctx->re, *ctx->re); ctx->re++; } break; @@ -1552,26 +1541,21 @@ tre_parse(tre_parse_ctx_t *ctx) { tre_ast_node_t *tmp1; tre_ast_node_t *tmp2; - tmp1 = tre_ast_new_literal(ctx->mem, 0, L'\n' - 1, - ctx->position); + tmp1 = tre_ast_new_literal(ctx->mem, 0, L'\n' - 1); if (!tmp1) return REG_ESPACE; - tmp2 = tre_ast_new_literal(ctx->mem, L'\n' + 1, TRE_CHAR_MAX, - ctx->position + 1); + tmp2 = tre_ast_new_literal(ctx->mem, L'\n' + 1, TRE_CHAR_MAX); if (!tmp2) return REG_ESPACE; result = tre_ast_new_union(ctx->mem, tmp1, tmp2); if (!result) return REG_ESPACE; - ctx->position += 2; } else { - result = tre_ast_new_literal(ctx->mem, 0, TRE_CHAR_MAX, - ctx->position); + result = tre_ast_new_literal(ctx->mem, 0, TRE_CHAR_MAX); if (!result) return REG_ESPACE; - ctx->position++; } ctx->re++; break; @@ -1588,7 +1572,7 @@ tre_parse(tre_parse_ctx_t *ctx) DPRINT(("tre_parse: BOL: '%.*" STRF "'\n", REST(ctx->re))); result = tre_ast_new_literal(ctx->mem, ASSERTION, - ASSERT_AT_BOL, -1); + ASSERT_AT_BOL); if (result == NULL) return REG_ESPACE; ctx->re++; @@ -1609,7 +1593,7 @@ tre_parse(tre_parse_ctx_t *ctx) DPRINT(("tre_parse: EOL: '%.*" STRF "'\n", REST(ctx->re))); result = tre_ast_new_literal(ctx->mem, ASSERTION, - ASSERT_AT_EOL, -1); + ASSERT_AT_EOL); if (result == NULL) return REG_ESPACE; ctx->re++; @@ -1656,7 +1640,7 @@ tre_parse(tre_parse_ctx_t *ctx) { DPRINT(("tre_parse: empty: '%.*" STRF "'\n", REST(ctx->re))); - result = tre_ast_new_literal(ctx->mem, EMPTY, -1, -1); + result = tre_ast_new_literal(ctx->mem, EMPTY, -1); if (!result) return REG_ESPACE; break; @@ -1682,13 +1666,11 @@ tre_parse(tre_parse_ctx_t *ctx) could be several opposite-case counterpoints, but they cannot be supported portably anyway. */ tmp1 = tre_ast_new_literal(ctx->mem, tre_toupper(*ctx->re), - tre_toupper(*ctx->re), - ctx->position); + tre_toupper(*ctx->re)); if (!tmp1) return REG_ESPACE; tmp2 = tre_ast_new_literal(ctx->mem, tre_tolower(*ctx->re), - tre_tolower(*ctx->re), - ctx->position); + tre_tolower(*ctx->re)); if (!tmp2) return REG_ESPACE; result = tre_ast_new_union(ctx->mem, tmp1, tmp2); @@ -1697,12 +1679,10 @@ tre_parse(tre_parse_ctx_t *ctx) } else { - result = tre_ast_new_literal(ctx->mem, *ctx->re, *ctx->re, - ctx->position); + result = tre_ast_new_literal(ctx->mem, *ctx->re, *ctx->re); if (!result) return REG_ESPACE; } - ctx->position++; ctx->re++; break; } @@ -1715,7 +1695,7 @@ tre_parse(tre_parse_ctx_t *ctx) if (result->submatch_id >= 0) { tre_ast_node_t *n, *tmp_node; - n = tre_ast_new_literal(ctx->mem, EMPTY, -1, -1); + n = tre_ast_new_literal(ctx->mem, EMPTY, -1); if (n == NULL) return REG_ESPACE; tmp_node = tre_ast_new_catenation(ctx->mem, n, result); diff --git a/lib/tre-parse.h b/lib/tre-parse.h index 3a7b7e0..f519714 100644 --- a/lib/tre-parse.h +++ b/lib/tre-parse.h @@ -26,8 +26,6 @@ typedef struct { int len; /* Current submatch ID. */ int submatch_id; - /* Current position (number of literal). */ - int position; /* The highest back reference or -1 if none seen so far. */ int max_backref; /* This flag is set if the regexp uses approximate matching. */