hush: optimize #[#] and %[%] for speed. size -2 bytes.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>

3 files changed, 87 insertions, 70 deletions

diff --git a/shell/hush.c b/shell/hush.c
index d3dab5863..4f80b7d83 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -2829,23 +2829,21 @@ static NOINLINE int expand_vars_to_list(o_string *output, int n, char *arg, char
          * Then var's value is matched to it and matching part removed.
          */
                                         if (val) {
-                                                bool match_at_left;
+                                                char *exp_exp_word;
                                                 char *loc;
-                                                scan_t scan = pick_scan(exp_op, *exp_word, &match_at_left);
+                                                unsigned scan_flags = pick_scan(exp_op, *exp_word);
                                                 if (exp_op == *exp_word)        /* ## or %% */
                                                         exp_word++;
                                                 val = to_be_freed = xstrdup(val);
-                                                {
-                                                        char *exp_exp_word = expand_pseudo_dquoted(exp_word);
-                                                        if (exp_exp_word)
-                                                                exp_word = exp_exp_word;
-                                                        loc = scan(to_be_freed, exp_word, match_at_left);
-                                                        //bb_error_msg("op:%c str:'%s' pat:'%s' res:'%s'",
-                                                        //              exp_op, to_be_freed, exp_word, loc);
-                                                        free(exp_exp_word);
-                                                }
+                                                exp_exp_word = expand_pseudo_dquoted(exp_word);
+                                                if (exp_exp_word)
+                                                        exp_word = exp_exp_word;
+                                                loc = scan_and_match(to_be_freed, exp_word, scan_flags);
+                                                //bb_error_msg("op:%c str:'%s' pat:'%s' res:'%s'",
+                                                //              exp_op, to_be_freed, exp_word, loc);
+                                                free(exp_exp_word);
                                                 if (loc) { /* match was found */
-                                                        if (match_at_left) /* # or ## */
+                                                        if (scan_flags & SCAN_MATCH_LEFT_HALF) /* # or ## */
                                                                 val = loc;
                                                         else /* % or %% */
                                                                 *loc = '\0';
diff --git a/shell/match.c b/shell/match.c
index 01b843918..e77c5d732 100644
--- a/shell/match.c
+++ b/shell/match.c
@@ -18,6 +18,9 @@
 # include <stdlib.h>
 # include <string.h>
 # include <unistd.h>
+# define FAST_FUNC /* nothing */
+# define PUSH_AND_SET_FUNCTION_VISIBILITY_TO_HIDDEN /* nothing */
+# define POP_SAVED_FUNCTION_VISIBILITY /* nothing */
 #else
 # include "libbb.h"
 #endif
@@ -26,16 +29,48 @@
 
 #define pmatch(a, b) !fnmatch((a), (b), 0)
 
-char *scanleft(char *string, char *pattern, bool match_at_left)
+char* FAST_FUNC scan_and_match(char *string, const char *pattern, unsigned flags)
 {
-        char c;
-        char *loc = string;
+        char *loc;
+        char *end;
+        unsigned len = strlen(string);
+        int early_exit;
+
+        /* We can stop the scan early only if the string part
+         * we are matching against is shrinking, and the pattern has
+         * an unquoted "star" at the corresponding end. There are two cases.
+         * Case 1:
+         * "qwerty" does not match against pattern "*zy",
+         * no point in trying to match "werty", "erty" etc:
+         */
+        early_exit = (flags == (SCAN_MOVE_FROM_LEFT + SCAN_MATCH_RIGHT_HALF) && pattern[0] == '*');
+
+        if (flags & SCAN_MOVE_FROM_LEFT) {
+                loc = string;
+                end = string + len + 1;
+        } else {
+                loc = string + len;
+                end = string - 1;
+                if (flags == (SCAN_MOVE_FROM_RIGHT + SCAN_MATCH_LEFT_HALF)) {
+                        /* Case 2:
+                         * "qwerty" does not match against pattern "qz*",
+                         * no point in trying to match "qwert", "qwer" etc:
+                         */
+                        const char *p = pattern + strlen(pattern);
+                        if (--p >= pattern && *p == '*') {
+                                early_exit = 1;
+                                while (--p >= pattern && *p == '\\')
+                                        early_exit ^= 1;
+                        }
+                }
+        }
 
-        while (1) {
+        while (loc != end) {
+                char c;
                 int match;
 
                 c = *loc;
-                if (match_at_left) {
+                if (flags & SCAN_MATCH_LEFT_HALF) {
                         *loc = '\0';
                         match = pmatch(pattern, string);
                         *loc = c;
@@ -44,33 +79,19 @@ char *scanleft(char *string, char *pattern, bool match_at_left)
                 }
                 if (match)
                         return loc;
-                if (!c)
-                        return NULL;
-                loc++;
-        }
-}
-
-char *scanright(char *string, char *pattern, bool match_at_left)
-{
-        char c;
-        char *loc = string + strlen(string);
-
-        while (loc >= string) {
-                int match;
+                if (early_exit) {
+#ifdef STANDALONE
+                        printf("(early exit) ");
+#endif
+                        break;
+                }
 
-                c = *loc;
-                if (match_at_left) {
-                        *loc = '\0';
-                        match = pmatch(pattern, string);
-                        *loc = c;
+                if (flags & SCAN_MOVE_FROM_LEFT) {
+                        loc++;
                 } else {
-                        match = pmatch(pattern, loc);
+                        loc--;
                 }
-                if (match)
-                        return loc;
-                loc--;
         }
-
         return NULL;
 }
 
@@ -80,12 +101,11 @@ int main(int argc, char *argv[])
         char *string;
         char *op;
         char *pattern;
-        bool match_at_left;
         char *loc;
 
-        int i;
+        setvbuf(stdout, NULL, _IONBF, 0);
 
-        if (argc == 1) {
+        if (!argv[1]) {
                 puts(
                         "Usage: match <test> [test...]\n\n"
                         "Where a <test> is the form: <string><op><match>\n"
@@ -95,36 +115,34 @@ int main(int argc, char *argv[])
                 return 1;
         }
 
-        for (i = 1; i < argc; ++i) {
+        while (*++argv) {
                 size_t off;
-                scan_t scan;
-
-                printf("'%s': ", argv[i]);
+                unsigned scan_flags;
 
-                string = strdup(argv[i]);
+                string = *argv;
                 off = strcspn(string, "#%");
                 if (!off) {
                         printf("invalid format\n");
-                        free(string);
                         continue;
                 }
                 op = string + off;
-                scan = pick_scan(op[0], op[1], &match_at_left);
+                scan_flags = pick_scan(op[0], op[1]);
+
+                printf("'%s': flags:%x, ", string, scan_flags);
                 pattern = op + 1;
                 if (op[0] == op[1])
-                        op[1] = '\0', ++pattern;
+                        pattern++;
                 op[0] = '\0';
 
-                loc = scan(string, pattern, match_at_left);
+                loc = scan_and_match(string, pattern, scan_flags);
 
-                if (match_at_left) {
+                if (scan_flags & SCAN_MATCH_LEFT_HALF) {
                         printf("'%s'\n", loc);
                 } else {
-                        *loc = '\0';
+                        if (loc)
+                                *loc = '\0';
                         printf("'%s'\n", string);
                 }
-
-                free(string);
         }
 
         return 0;
diff --git a/shell/match.h b/shell/match.h
index c022ceb25..aa393ed1a 100644
--- a/shell/match.h
+++ b/shell/match.h
@@ -7,25 +7,26 @@ PUSH_AND_SET_FUNCTION_VISIBILITY_TO_HIDDEN
 
 //TODO! Why ash.c still uses internal version?!
 
-typedef char *(*scan_t)(char *string, char *match, bool match_at_left);
+enum {
+        SCAN_MOVE_FROM_LEFT = (1 << 0),
+        SCAN_MOVE_FROM_RIGHT = (1 << 1),
+        SCAN_MATCH_LEFT_HALF = (1 << 2),
+        SCAN_MATCH_RIGHT_HALF = (1 << 3),
+};
 
-char *scanleft(char *string, char *match, bool match_at_left);
-char *scanright(char *string, char *match, bool match_at_left);
+char* FAST_FUNC scan_and_match(char *string, const char *pattern, unsigned flags);
 
-static inline scan_t pick_scan(char op1, char op2, bool *match_at_left)
+static inline unsigned pick_scan(char op1, char op2)
 {
-        /* #  - scanleft
-         * ## - scanright
-         * %  - scanright
-         * %% - scanleft
-         */
+        unsigned scan_flags;
         if (op1 == '#') {
-                *match_at_left = true;
-                return op1 == op2 ? scanright : scanleft;
-        } else {
-                *match_at_left = false;
-                return op1 == op2 ? scanleft : scanright;
+                scan_flags = SCAN_MATCH_LEFT_HALF +
+                        (op1 == op2 ? SCAN_MOVE_FROM_RIGHT : SCAN_MOVE_FROM_LEFT);
+        } else { /* % */
+                scan_flags = SCAN_MATCH_RIGHT_HALF +
+                        (op1 == op2 ? SCAN_MOVE_FROM_LEFT : SCAN_MOVE_FROM_RIGHT);
         }
+        return scan_flags;
 }
 
 POP_SAVED_FUNCTION_VISIBILITY