vi: fix backward search with GNU regex

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>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 13 insertions, 20 deletions

diff --git a/editors/vi.c b/editors/vi.c
index b06270dfd..0baea615b 100644
--- a/editors/vi.c
+++ b/editors/vi.c
@@ -2376,9 +2376,7 @@ 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)
@@ -2403,31 +2401,26 @@ 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