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Tweak re_registers allocation

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* src/regex-emacs.c (re_match_2_internal):
No need to allocate one extra trailing search register;
Emacs does not use it.  Avoid quadratic behavior on
reallocation.
This commit is contained in:
Paul Eggert 2019-03-27 21:03:10 -07:00
parent eac5f967ca
commit 81795bb713
2 changed files with 10 additions and 18 deletions
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26
src/regex-emacs.c
View file

@ -3940,8 +3940,7 @@ re_match_2_internal (struct re_pattern_buffer *bufp,
}
/* Initialize subexpression text positions to -1 to mark ones that no
start_memory/stop_memory has been seen for. Also initialize the
register information struct. */
start_memory/stop_memory has been seen for. */
for (ptrdiff_t reg = 1; reg < num_regs; reg++)
regstart[reg] = regend[reg] = NULL;
@ -4091,10 +4090,8 @@ re_match_2_internal (struct re_pattern_buffer *bufp,
{
/* Have the register data arrays been allocated? */
if (bufp->regs_allocated == REGS_UNALLOCATED)
{ /* No. So allocate them with malloc. We need one
extra element beyond 'num_regs' for the '-1' marker
GNU code uses. */
ptrdiff_t n = max (RE_NREGS, num_regs + 1);
{ /* No. So allocate them with malloc. */
ptrdiff_t n = max (RE_NREGS, num_regs);
regs->start = xnmalloc (n, sizeof *regs->start);
regs->end = xnmalloc (n, sizeof *regs->end);
regs->num_regs = n;
@ -4104,9 +4101,10 @@ re_match_2_internal (struct re_pattern_buffer *bufp,
{ /* Yes. If we need more elements than were already
allocated, reallocate them. If we need fewer, just
leave it alone. */
if (regs->num_regs < num_regs + 1)
ptrdiff_t n = regs->num_regs;
if (n < num_regs)
{
ptrdiff_t n = num_regs + 1;
n = max (n + (n >> 1), num_regs);
regs->start
= xnrealloc (regs->start, n, sizeof *regs->start);
regs->end = xnrealloc (regs->end, n, sizeof *regs->end);
@ -4137,10 +4135,7 @@ re_match_2_internal (struct re_pattern_buffer *bufp,
}
/* If the regs structure we return has more elements than
were in the pattern, set the extra elements to -1. If
we (re)allocated the registers, this is the case,
because we always allocate enough to have at least one
-1 at the end. */
were in the pattern, set the extra elements to -1. */
for (ptrdiff_t reg = num_regs; reg < regs->num_regs; reg++)
regs->start[reg] = regs->end[reg] = -1;
}
@ -5053,13 +5048,10 @@ re_compile_pattern (const char *pattern, ptrdiff_t length,
bool posix_backtracking, const char *whitespace_regexp,
struct re_pattern_buffer *bufp)
{
reg_errcode_t ret;
/* GNU code is written to assume at least RE_NREGS registers will be set
(and at least one extra will be -1). */
bufp->regs_allocated = REGS_UNALLOCATED;
ret = regex_compile ((re_char *) pattern, length,
reg_errcode_t ret
= regex_compile ((re_char *) pattern, length,
posix_backtracking,
whitespace_regexp,
bufp);

2
src/regex-emacs.h
View file

@ -98,7 +98,7 @@ struct re_pattern_buffer
bool_bf can_be_null : 1;
/* If REGS_UNALLOCATED, allocate space in the 'regs' structure
for 'max (RE_NREGS, re_nsub + 1)' groups.
for at least (re_nsub + 1) groups.
If REGS_REALLOCATE, reallocate space if necessary.
If REGS_FIXED, use what's there. */
unsigned regs_allocated : 2;