preproc: Extract reading line from predefined macros from read_line

It makes read_line less complex

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

preproc.c

@@ -680,31 +680,29 @@ hash_findix(struct hash_table *hash, const char *str)
     return p ? *p : NULL;
 }
 
-#define BUF_DELTA 512
 /*
- * Read a line from the top file in istk, handling multiple CR/LFs
- * at the end of the line read, and handling spurious ^Zs. Will
- * return lines from the standard macro set if this has not already
- * been done.
+ * read line from standart macros set,
+ * if there no more left -- return NULL
  */
-static char *read_line(void)
+static char *line_from_stdmac(void)
 {
-    char *buffer, *p, *q;
-    int bufsize, continued_count;
-
-    if (stdmacpos) {
     unsigned char c;
     const unsigned char *p = stdmacpos;
-        char *ret, *q;
+    char *line, *q;
     size_t len = 0;
+
+    if (!stdmacpos)
+        return NULL;
+
     while ((c = *p++)) {
         if (c >= 0x80)
             len += pp_directives_len[c - 0x80] + 1;
         else
             len++;
     }
-        ret = nasm_malloc(len+1);
-        q = ret;
+
+    line = nasm_malloc(len + 1);
+    q = line;
     while ((c = *stdmacpos++)) {
         if (c >= 0x80) {
             memcpy(q, pp_directives[c - 0x80], pp_directives_len[c - 0x80]);
@@ -741,18 +739,43 @@ static char *read_line(void)
                     *tail = new_Token(NULL, t->type, t->text, 0);
                     tail = &(*tail)->next;
                 }
+
                 l           = nasm_malloc(sizeof(Line));
                 l->next     = istk->expansion;
                 l->first    = head;
                 l->finishes = NULL;
+
                 istk->expansion = l;
             }
             do_predef = false;
         }
     }
-        return ret;
+
+    return line;
 }
 
+#define BUF_DELTA 512
+/*
+ * Read a line from the top file in istk, handling multiple CR/LFs
+ * at the end of the line read, and handling spurious ^Zs. Will
+ * return lines from the standard macro set if this has not already
+ * been done.
+ */
+static char *read_line(void)
+{
+    char *buffer, *p, *q;
+    int bufsize, continued_count;
+
+    /*
+     * standart macros set (predefined) goes first
+     */
+    p = line_from_stdmac();
+    if (p)
+        return p;
+
+    /*
+     * regular read from a file
+     */
     bufsize = BUF_DELTA;
     buffer = nasm_malloc(BUF_DELTA);
     p = buffer;