bc: shrink zdc_lex_string()

This actually fixes a rather obscure bug. This was failing to find
end of the string:

	$ echo -n '[foo]' | dc
	dc: string end could not be found

function                                             old     new   delta
zbc_lex_next                                        2230    2141     -89
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-89)             Total: -89 bytes
   text	   data	    bss	    dec	    hex	filename
 981461	    485	   7296	 989242	  f183a	busybox_old
 981372	    485	   7296	 989153	  f17e1	busybox_unstripped

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

1 files changed, 19 insertions, 13 deletions

diff --git a/miscutils/bc.c b/miscutils/bc.c
index 37c9012f9..5d969c9d0 100644
--- a/miscutils/bc.c
+++ b/miscutils/bc.c
@@ -3272,25 +3272,31 @@ static BC_STATUS zdc_lex_register(BcLex *l)
 
 static BC_STATUS zdc_lex_string(BcLex *l)
 {
-        size_t depth = 1, nls = 0, i = l->i;
-        char c;
+        size_t depth, nls, i;
 
         l->t.t = BC_LEX_STR;
         bc_vec_pop_all(&l->t.v);
 
-        for (c = l->buf[i]; c != 0 && depth; c = l->buf[++i]) {
-
-                depth += (c == '[' && (i == l->i || l->buf[i - 1] != '\\'));
-                depth -= (c == ']' && (i == l->i || l->buf[i - 1] != '\\'));
+        nls = 0;
+        depth = 1;
+        i = l->i;
+        for (;;) {
+                char c = l->buf[i];
+                if (c == '\0') {
+                        l->i = i;
+                        RETURN_STATUS(bc_error("string end could not be found"));
+                }
                 nls += (c == '\n');
-
-                if (depth) bc_vec_push(&l->t.v, &c);
-        }
-
-        if (c == '\0') {
-                l->i = i;
-                RETURN_STATUS(bc_error("string end could not be found"));
+                if (i == l->i || l->buf[i - 1] != '\\') {
+                        if (c == '[') depth++;
+                        if (c == ']')
+                                if (--depth == 0)
+                                        break;
+                }
+                bc_vec_push(&l->t.v, &l->buf[i]);
+                i++;
         }
+        i++;
 
         bc_vec_pushZeroByte(&l->t.v);
         // This check makes sense only if size_t is (much) larger than BC_MAX_STRING.