hush: optimization: do not glob words "[" and "[["

function                                             old     new   delta
glob_needed                                           71      86     +15

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

1 files changed, 40 insertions, 0 deletions

diff --git a/shell/hush.c b/shell/hush.c
index 09ab6ebc0..6129a087b 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -115,6 +115,11 @@
 //config:# It's only needed to get "nice" menuconfig indenting.
 //config:if SHELL_HUSH || HUSH || SH_IS_HUSH || BASH_IS_HUSH
 //config:
+//config:config HUSH_NEED_FOR_SPEED
+//config:       bool "Faster, but larger code"
+//config:       default y
+//config:       depends on SHELL_HUSH
+//config:
 //config:config HUSH_BASH_COMPAT
 //config:       bool "bash-compatible extensions"
 //config:       default y
@@ -3381,6 +3386,24 @@ static int o_get_last_ptr(o_string *o, int n)
 /* Helper */
 static int glob_needed(const char *s)
 {
+# if ENABLE_HUSH_NEED_FOR_SPEED
+        char c = *s;
+        if (c == '[' /*|| c == '{'*/) {
+                /* Special-case words consisting entirely of [.
+                 * Optimization to avoid glob()
+                 * on "[ COND ]" and "[[ COND ]]":
+                 *  strace hush -c 'i=0; while [ $((++i)) != 50000 ]; do :; done'
+                 * shouldn't be doing 50000 stat("[").
+                 * (Can do it for "{" too, but it's not a common case).
+                 */
+                const char *p = s;
+                while (*++p == c)
+                        continue;
+                if (*p == '\0')
+                        return 0;
+        }
+# endif
+
         while (*s) {
                 if (*s == '\\') {
                         if (!s[1])
@@ -3572,6 +3595,23 @@ static int perform_glob(o_string *o, int n)
 /* Helper */
 static int glob_needed(const char *s)
 {
+# if ENABLE_HUSH_NEED_FOR_SPEED
+        char c = *s;
+        if (c == '[') {
+                /* Special-case words consisting entirely of [.
+                 * Optimization to avoid glob()
+                 * on "[ COND ]" and "[[ COND ]]":
+                 *  strace hush -c 'i=0; while [ $((++i)) != 50000 ]; do :; done'
+                 * shouldn't be doing 50000 stat("[").
+                 */
+                const char *p = s;
+                while (*++p == c)
+                        continue;
+                if (*p == '\0')
+                        return 0;
+        }
+# endif
+
         while (*s) {
                 if (*s == '\\') {
                         if (!s[1])