ash.c: speedup ${s:} substring (no quotes)

This trivial patch makes ${s:...} at least as fast as ${s#??..}
in simple tests. It's probably faster for longer substrings,
but then one wouldn't use ${s#"1024???s"} anyway -
one would switch away from sh.

function                                             old     new   delta
subevalvar                                          1457    1503     +46

Signed-off-by: Alin Mr <almr.oss@outlook.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 11 insertions, 6 deletions

diff --git a/shell/ash.c b/shell/ash.c
index 7b85981ec..e8ec0b1a6 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -7185,14 +7185,19 @@ subevalvar(char *start, char *str, int strloc,
                 if ((unsigned)len > (orig_len - pos))
                         len = orig_len - pos;
 
-                for (vstr = startp; pos; vstr++, pos--) {
-                        if (quotes && (unsigned char)*vstr == CTLESC)
+                if (!quotes) {
+                        loc = mempcpy(startp, startp + pos, len);
+                } else {
+                        for (vstr = startp; pos != 0; pos--) {
+                                if ((unsigned char)*vstr == CTLESC)
+                                        vstr++;
                                 vstr++;
-                }
-                for (loc = startp; len; len--) {
-                        if (quotes && (unsigned char)*vstr == CTLESC)
+                        }
+                        for (loc = startp; len != 0; len--) {
+                                if ((unsigned char)*vstr == CTLESC)
+                                        *loc++ = *vstr++;
                                 *loc++ = *vstr++;
-                        *loc++ = *vstr++;
+                        }
                 }
                 *loc = '\0';
                 goto out;