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List:       busybox
Subject:    Re: [PATCH] vi: fix backward search with GNU regex
From:       Denys Vlasenko <vda.linux () googlemail ! com>
Date:       2021-06-21 13:38:35
Message-ID: CAK1hOcPtHhYjvo2Q3u4tWw_Y88v4Ae_LUda=S9tzb20pS98whA () mail ! gmail ! com
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Applied, thank you

On Mon, Jun 21, 2021 at 12:31 PM Ron Yorston <rmy@pobox.com> wrote:
>
> With FEATURE_VI_REGEX_SEARCH enabled backward searches don't work.
> This is problematic on distros that enable regexes, such as Tiny
> Core Linux and Fedora.
>
> When calling GNU re_search() with a negative range parameter
> (indicating a backward search) the start offset must be set to
> the end of the area being searched.
>
> The return value of re_search() is the offset of the matched pattern
> from the start of the area being searched.  For a successful search
> (positive return value) char_search() can return the pointer to
> the start of the area plus the offset.
>
> FEATURE_VI_REGEX_SEARCH isn't enabled by default but when it is:
>
> function                                             old     new   delta
> char_search                                          256     247      -9
> ------------------------------------------------------------------------------
> (add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-9)               Total: -9 bytes
>
> Signed-off-by: Andrey Dobrovolsky <andrey.dobrovolsky.odessa@gmail.com>
> Signed-off-by: Ron Yorston <rmy@pobox.com>
> ---
>  editors/vi.c | 33 +++++++++++++--------------------
>  1 file changed, 13 insertions(+), 20 deletions(-)
>
> diff --git a/editors/vi.c b/editors/vi.c
> index d85cdd98d..87d6a628e 100644
> --- a/editors/vi.c
> +++ b/editors/vi.c
> @@ -2371,9 +2371,7 @@ static char *char_search(char *p, const char *pat, int dir_and_range)
>         struct re_pattern_buffer preg;
>         const char *err;
>         char *q;
> -       int i;
> -       int size;
> -       int range;
> +       int i, size, range, start;
>
>         re_syntax_options = RE_SYNTAX_POSIX_EXTENDED;
>         if (ignorecase)
> @@ -2398,31 +2396,26 @@ static char *char_search(char *p, const char *pat, int dir_and_range)
>
>         // RANGE could be negative if we are searching backwards
>         range = q - p;
> -       q = p;
> -       size = range;
>         if (range < 0) {
> -               size = -size;
> -               q = p - size;
> -               if (q < text)
> -                       q = text;
> +               size = -range;
> +               start = size;
> +       } else {
> +               size = range;
> +               start = 0;
>         }
> +       q = p - start;
> +       if (q < text)
> +               q = text;
>         // search for the compiled pattern, preg, in p[]
> -       // range < 0: search backward
> -       // range > 0: search forward
> -       // 0 < start < size
> +       // range < 0, start == size: search backward
> +       // range > 0, start == 0: search forward
>         // re_search() < 0: not found or error
>         // re_search() >= 0: index of found pattern
>         //           struct pattern   char     int   int    int    struct reg
>         // re_search(*pattern_buffer, *string, size, start, range, *regs)
> -       i = re_search(&preg, q, size, /*start:*/ 0, range, /*struct re_registers*:*/ NULL);
> +       i = re_search(&preg, q, size, start, range, /*struct re_registers*:*/ NULL);
>         regfree(&preg);
> -       if (i < 0)
> -               return NULL;
> -       if (dir_and_range > 0) // FORWARD?
> -               p = p + i;
> -       else
> -               p = p - i;
> -       return p;
> +       return i < 0 ? NULL : q + i;
>  }
>  # else
>  #  if ENABLE_FEATURE_VI_SETOPTS
> --
> 2.31.1
>
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