awk: speed improvementsawk_faster

Improve performance in certain cases at the cost of an additional
144 bytes in the binary.

- Reinstate (and fix) the original code to speed up assignment of a
  temporary string to a variable.

- Replace use of xasprintf() for string concatentation with explicit
  string manipulation.  This could be faster still if Windows had an
  optimised stpcpy().

The enhancement is not enabled by default.

This test case:

   BEGIN{while(++i<30000) s=s i}

is 18 times faster.  The less extreme:

   BEGIN{while(++i<1000000) s="abc " i}

is 30% faster.

See GitHub issue #193.

1 files changed, 27 insertions, 8 deletions

diff --git a/editors/awk.c b/editors/awk.c
index 509f4ddd8..57d354858 100644
--- a/editors/awk.c
+++ b/editors/awk.c
@@ -30,6 +30,14 @@
 //config:       * simultaneous use of -f and -e on the command line.
 //config:       This enables the use of awk library files.
 //config:       Example: awk -f mylib.awk -e '{print myfunction($1);}' ...
+//config:config FEATURE_AWK_FASTER
+//config:       bool "Enable some speed enhancements"
+//config:       default n
+//config:       depends on AWK
+//config:       help
+//config:       Enable enhancements that speed up string concatenation and
+//config:       assignment of temporary strings to a variable.  Increases
+//config:       size of binary by 144 bytes.
 
 //applet:IF_AWK(APPLET_NOEXEC(awk, awk, BB_DIR_USR_BIN, BB_SUID_DROP, awk))
 
@@ -2766,15 +2774,14 @@ static var *evaluate(node *op, var *res)
 
                 case XC( OC_MOVE ):
                         debug_printf_eval("MOVE\n");
-                        /* if source is a temporary string, jusk relink it to dest */
-//Disabled: if R.v is numeric but happens to have cached R.v->string,
-//then L.v ends up being a string, which is wrong
-//                      if (R.v == v1+1 && R.v->string) {
-//                              res = setvar_p(L.v, R.v->string);
-//                              R.v->string = NULL;
-//                      } else {
+#if ENABLE_FEATURE_AWK_FASTER
+                        /* if source is a temporary string, just relink it to dest */
+                        if (R.v == v1+1 && R.v->string && !(R.v->type & VF_NUMBER)) {
+                                res = setvar_p(L.v, R.v->string);
+                                R.v->string = NULL;
+                        } else
+#endif
                                 res = copyvar(L.v, R.v);
-//                      }
                         break;
 
                 case XC( OC_TERNARY ):
@@ -3025,9 +3032,21 @@ static var *evaluate(node *op, var *res)
                 case XC( OC_CONCAT ):
                 case XC( OC_COMMA ): {
                         const char *sep = "";
+#if ENABLE_FEATURE_AWK_FASTER
+                        char *buf;
+#endif
                         if ((opinfo & OPCLSMASK) == OC_COMMA)
                                 sep = getvar_s(intvar[SUBSEP]);
+#if ENABLE_FEATURE_AWK_FASTER
+                        buf = xmalloc(strlen(L.s) + strlen(sep) + strlen(R.s) + 1);
+                        strcpy(buf, L.s);
+                        if (*sep != '\0')
+                                strcat(buf, sep);
+                        strcat(buf, R.s);
+                        setvar_p(res, buf);
+#else
                         setvar_p(res, xasprintf("%s%s%s", L.s, sep, R.s));
+#endif
                         break;
                 }