-
-/* We are passed P pointing to a register number after a start_memory.
-
- Return true if the pattern up to the corresponding stop_memory can
- match the empty string, and false otherwise.
-
- If we find the matching stop_memory, sets P to point to one past its number.
- Otherwise, sets P to an undefined byte less than or equal to END.
-
- We don't handle duplicates properly (yet). */
-
-static boolean
-group_match_null_string_p (p, end, reg_info)
- unsigned char **p, *end;
- register_info_type *reg_info;
-{
- int mcnt;
- /* Point to after the args to the start_memory. */
- unsigned char *p1 = *p + 2;
-
- while (p1 < end)
- {
- /* Skip over opcodes that can match nothing, and return true or
- false, as appropriate, when we get to one that can't, or to the
- matching stop_memory. */
-
- switch ((re_opcode_t) *p1)
- {
- /* Could be either a loop or a series of alternatives. */
- case on_failure_jump:
- p1++;
- EXTRACT_NUMBER_AND_INCR (mcnt, p1);
-
- /* If the next operation is not a jump backwards in the
- pattern. */
-
- if (mcnt >= 0)
- {
- /* Go through the on_failure_jumps of the alternatives,
- seeing if any of the alternatives cannot match nothing.
- The last alternative starts with only a jump,
- whereas the rest start with on_failure_jump and end
- with a jump, e.g., here is the pattern for `a|b|c':
-
- /on_failure_jump/0/6/exactn/1/a/jump_past_alt/0/6
- /on_failure_jump/0/6/exactn/1/b/jump_past_alt/0/3
- /exactn/1/c
-
- So, we have to first go through the first (n-1)
- alternatives and then deal with the last one separately. */
-
-
- /* Deal with the first (n-1) alternatives, which start
- with an on_failure_jump (see above) that jumps to right
- past a jump_past_alt. */
-
- while ((re_opcode_t) p1[mcnt-3] == jump_past_alt)
- {
- /* `mcnt' holds how many bytes long the alternative
- is, including the ending `jump_past_alt' and
- its number. */
-
- if (!alt_match_null_string_p (p1, p1 + mcnt - 3,
- reg_info))
- return false;
-
- /* Move to right after this alternative, including the
- jump_past_alt. */
- p1 += mcnt;
-
- /* Break if it's the beginning of an n-th alternative
- that doesn't begin with an on_failure_jump. */
- if ((re_opcode_t) *p1 != on_failure_jump)
- break;
-
- /* Still have to check that it's not an n-th
- alternative that starts with an on_failure_jump. */
- p1++;
- EXTRACT_NUMBER_AND_INCR (mcnt, p1);
- if ((re_opcode_t) p1[mcnt-3] != jump_past_alt)
- {
- /* Get to the beginning of the n-th alternative. */
- p1 -= 3;
- break;
- }
- }
-
- /* Deal with the last alternative: go back and get number
- of the `jump_past_alt' just before it. `mcnt' contains
- the length of the alternative. */
- EXTRACT_NUMBER (mcnt, p1 - 2);
-
- if (!alt_match_null_string_p (p1, p1 + mcnt, reg_info))
- return false;
-
- p1 += mcnt; /* Get past the n-th alternative. */
- } /* if mcnt > 0 */
- break;
-
-
- case stop_memory:
- assert (p1[1] == **p);
- *p = p1 + 2;
- return true;
-
-
- default:
- if (!common_op_match_null_string_p (&p1, end, reg_info))
- return false;
- }
- } /* while p1 < end */
-
- return false;
-} /* group_match_null_string_p */
-
-
-/* Similar to group_match_null_string_p, but doesn't deal with alternatives:
- It expects P to be the first byte of a single alternative and END one
- byte past the last. The alternative can contain groups. */
-
-static boolean
-alt_match_null_string_p (p, end, reg_info)
- unsigned char *p, *end;
- register_info_type *reg_info;
-{
- int mcnt;
- unsigned char *p1 = p;
-
- while (p1 < end)
- {
- /* Skip over opcodes that can match nothing, and break when we get
- to one that can't. */
-
- switch ((re_opcode_t) *p1)
- {
- /* It's a loop. */
- case on_failure_jump:
- p1++;
- EXTRACT_NUMBER_AND_INCR (mcnt, p1);
- p1 += mcnt;
- break;
-
- default:
- if (!common_op_match_null_string_p (&p1, end, reg_info))
- return false;
- }
- } /* while p1 < end */
-
- return true;
-} /* alt_match_null_string_p */
-
-
-/* Deals with the ops common to group_match_null_string_p and
- alt_match_null_string_p.
-
- Sets P to one after the op and its arguments, if any. */
-
-static boolean
-common_op_match_null_string_p (p, end, reg_info)
- unsigned char **p, *end;
- register_info_type *reg_info;
-{
- int mcnt;
- boolean ret;
- int reg_no;
- unsigned char *p1 = *p;
-
- switch ((re_opcode_t) *p1++)
- {
- case no_op:
- case begline:
- case endline:
- case begbuf:
- case endbuf:
- case wordbeg:
- case wordend:
- case wordbound:
- case notwordbound:
-#ifdef emacs
- case before_dot:
- case at_dot:
- case after_dot:
-#endif
- break;
-
- case start_memory:
- reg_no = *p1;
- assert (reg_no > 0 && reg_no <= MAX_REGNUM);
- ret = group_match_null_string_p (&p1, end, reg_info);
-
- /* Have to set this here in case we're checking a group which
- contains a group and a back reference to it. */
-
- if (REG_MATCH_NULL_STRING_P (reg_info[reg_no]) == MATCH_NULL_UNSET_VALUE)
- REG_MATCH_NULL_STRING_P (reg_info[reg_no]) = ret;
-
- if (!ret)
- return false;
- break;
-
- /* If this is an optimized succeed_n for zero times, make the jump. */
- case jump:
- EXTRACT_NUMBER_AND_INCR (mcnt, p1);
- if (mcnt >= 0)
- p1 += mcnt;
- else
- return false;
- break;
-
- case succeed_n:
- /* Get to the number of times to succeed. */
- p1 += 2;
- EXTRACT_NUMBER_AND_INCR (mcnt, p1);
-
- if (mcnt == 0)
- {
- p1 -= 4;
- EXTRACT_NUMBER_AND_INCR (mcnt, p1);
- p1 += mcnt;
- }
- else
- return false;
- break;
-
- case duplicate:
- if (!REG_MATCH_NULL_STRING_P (reg_info[*p1]))
- return false;
- break;
-
- case set_number_at:
- p1 += 4;
-
- default:
- /* All other opcodes mean we cannot match the empty string. */
- return false;
- }
-
- *p = p1;
- return true;
-} /* common_op_match_null_string_p */
-
-