awk: get rid of "move name one char back" trick in next_token()

function                                             old     new   delta
next_token                                           791     812     +21
awk_main                                             886     831     -55
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/1 up/down: 21/-55)            Total: -34 bytes

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

1 files changed, 27 insertions, 27 deletions

diff --git a/editors/awk.c b/editors/awk.c
index 1a4468a53..fb1e5d59b 100644
--- a/editors/awk.c
+++ b/editors/awk.c
@@ -535,6 +535,7 @@ struct globals {
         var *Fields;
         nvblock *g_cb;
         char *g_pos;
+        char g_saved_ch;
         smallint icase;
         smallint exiting;
         smallint nextrec;
@@ -599,6 +600,7 @@ struct globals2 {
 #define Fields       (G1.Fields      )
 #define g_cb         (G1.g_cb        )
 #define g_pos        (G1.g_pos       )
+#define g_saved_ch   (G1.g_saved_ch  )
 #define icase        (G1.icase       )
 #define exiting      (G1.exiting     )
 #define nextrec      (G1.nextrec     )
@@ -1125,6 +1127,10 @@ static uint32_t next_token(uint32_t expected)
                 t_info = save_info;
         } else {
                 p = g_pos;
+                if (g_saved_ch != '\0') {
+                        *p = g_saved_ch;
+                        g_saved_ch = '\0';
+                }
  readnext:
                 p = skip_spaces(p);
                 g_lineno = t_lineno;
@@ -1183,6 +1189,8 @@ static uint32_t next_token(uint32_t expected)
                         tc = TC_NUMBER;
                         debug_printf_parse("%s: token found:%f TC_NUMBER\n", __func__, t_double);
                 } else {
+                        char *end_of_name;
+
                         if (*p == '\n')
                                 t_lineno++;
 
@@ -1219,16 +1227,14 @@ static uint32_t next_token(uint32_t expected)
                         if (!isalnum_(*p))
                                 syntax_error(EMSG_UNEXP_TOKEN); /* no */
                         /* yes */
-/* "move name one char back" trick: we need a byte for NUL terminator */
-/* NB: this results in argv[i][-1] being used (!!!) in e.g. "awk -e 'NAME'" case */
-                        t_string = --p;
-                        while (isalnum_(*++p)) {
-                                p[-1] = *p;
-                        }
-                        p[-1] = '\0';
+                        t_string = p;
+                        while (isalnum_(*p))
+                                p++;
+                        end_of_name = p;
                         tc = TC_VARIABLE;
                         /* also consume whitespace between functionname and bracket */
                         if (!(expected & TC_VARIABLE) || (expected & TC_ARRAY))
+//TODO: why if variable can be here (but not array ref), skipping is not allowed? Example where it matters?
                                 p = skip_spaces(p);
                         if (*p == '(') {
                                 p++;
@@ -1240,7 +1246,19 @@ static uint32_t next_token(uint32_t expected)
                                 debug_printf_parse("%s: token found:'%s' TC_ARRAY\n", __func__, t_string);
                         } else {
                                 debug_printf_parse("%s: token found:'%s' TC_VARIABLE\n", __func__, t_string);
+                                if (end_of_name == p) {
+                                        /* there is no space for trailing NUL in t_string!
+                                         * We need to save the char we are going to NUL.
+                                         * (we'll use it in future call to next_token())
+                                         */
+                                        g_saved_ch = *end_of_name;
+// especially pathological example is V="abc"; V.2 - it's V concatenated to .2
+// (it evaluates to "abc0.2"). Because of this case, we can't simply cache
+// '.' and analyze it later: we also have to *store it back* in next
+// next_token(), in order to give my_strtod() the undamaged ".2" string.
+                                }
                         }
+                        *end_of_name = '\0'; /* terminate t_string */
                 }
  token_found:
                 g_pos = p;
@@ -3420,38 +3438,20 @@ int awk_main(int argc UNUSED_PARAM, char **argv)
 
                 g_progname = llist_pop(&list_f);
                 fd = xopen_stdin(g_progname);
-                /* 1st byte is reserved for "move name one char back" trick in next_token */
-                i = 1;
-                s = NULL;
-                for (;;) {
-                        int sz;
-                        s = xrealloc(s, i + 1000);
-                        sz = safe_read(fd, s + i, 1000);
-                        if (sz <= 0)
-                                break;
-                        i += sz;
-                }
-                s = xrealloc(s, i + 1); /* trim unused 999 bytes */
-                s[i] = '\0';
+                s = xmalloc_read(fd, NULL); /* it's NUL-terminated */
                 close(fd);
-                parse_program(s + 1);
+                parse_program(s);
                 free(s);
         }
         g_progname = "cmd. line";
 #if ENABLE_FEATURE_AWK_GNU_EXTENSIONS
         while (list_e) {
-                /* NB: "move name one char back" trick in next_token
-                 * can use argv[i][-1] here.
-                 */
                 parse_program(llist_pop(&list_e));
         }
 #endif
         if (!(opt & (OPT_f | OPT_e))) {
                 if (!*argv)
                         bb_show_usage();
-                /* NB: "move name one char back" trick in next_token
-                 * can use argv[i][-1] here.
-                 */
                 parse_program(*argv++);
         }