libbb: split bb_get_chunk_from_file and bb_get_chunk_with_continuation

This also moves bb_get_chunk_with_continuation into its sole user,
parse_config.c.
This allows to optimize both functions separately,
they need to be optimized for speed.
(this need was highlighted by slow modprobe caused in part by slow
bb_get_chunk_with_continuation in config parser).

function                                             old     new   delta
bb_get_chunk_from_file                                 7     130    +123
config_read                                          457     558    +101
bb_get_chunk_with_continuation                       194       -    -194
------------------------------------------------------------------------------
(add/remove: 0/1 grow/shrink: 2/0 up/down: 224/-194)           Total: 30 bytes

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

3 files changed, 56 insertions, 44 deletions

diff --git a/include/libbb.h b/include/libbb.h
index 2d46061da..5d2b4c8c1 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -730,8 +730,12 @@ extern void xclose(int fd) FAST_FUNC;
 /* Reads and prints to stdout till eof, then closes FILE. Exits on error: */
 extern void xprint_and_close_file(FILE *file) FAST_FUNC;
 
+/* Reads a line from a text file, up to a newline or NUL byte, inclusive.
+ * Returns malloc'ed char*. If end is NULL '\n' isn't considered
+ * end of line. If end isn't NULL, length of the chunk is stored in it.
+ * Returns NULL if EOF/error.
+ */
 extern char *bb_get_chunk_from_file(FILE *file, int *end) FAST_FUNC;
-extern char *bb_get_chunk_with_continuation(FILE *file, int *end, int *lineno) FAST_FUNC;
 /* Reads up to (and including) TERMINATING_STRING: */
 extern char *xmalloc_fgets_str(FILE *file, const char *terminating_string) FAST_FUNC RETURNS_MALLOC;
 /* Same, with limited max size, and returns the length (excluding NUL): */
diff --git a/libbb/get_line_from_file.c b/libbb/get_line_from_file.c
index 9be10687b..a98dd35eb 100644
--- a/libbb/get_line_from_file.c
+++ b/libbb/get_line_from_file.c
@@ -11,45 +11,24 @@
 
 #include "libbb.h"
 
-/* This function reads an entire line from a text file, up to a newline
- * or NUL byte, inclusive.  It returns a malloc'ed char * which
- * must be free'ed by the caller.  If end is NULL '\n' isn't considered
- * end of line.  If end isn't NULL, length of the chunk is stored in it.
- * If lineno is not NULL, *lineno is incremented for each line,
- * and also trailing '\' is recognized as line continuation.
- *
- * Returns NULL if EOF/error. */
-char* FAST_FUNC bb_get_chunk_with_continuation(FILE *file, int *end, int *lineno)
+char* FAST_FUNC bb_get_chunk_from_file(FILE *file, int *end)
 {
         int ch;
-        int idx = 0;
+        unsigned idx = 0;
         char *linebuf = NULL;
-        int linebufsz = 0;
 
         while ((ch = getc(file)) != EOF) {
                 /* grow the line buffer as necessary */
-                if (idx >= linebufsz) {
-                        linebufsz += 256;
-                        linebuf = xrealloc(linebuf, linebufsz);
-                }
+                if (!(idx & 0xff))
+                        linebuf = xrealloc(linebuf, idx + 0x100);
                 linebuf[idx++] = (char) ch;
-                if (!ch)
+                if (ch == '\0')
+                        break;
+                if (end && ch == '\n')
                         break;
-                if (end && ch == '\n') {
-                        if (lineno == NULL)
-                                break;
-                        (*lineno)++;
-                        if (idx < 2 || linebuf[idx-2] != '\\')
-                                break;
-                        idx -= 2;
-                }
         }
-        if (end) {
+        if (end)
                 *end = idx;
-                /* handle corner case when the file is not ended with '\n' */
-                if (ch == EOF && lineno != NULL)
-                        (*lineno)++;
-        }
         if (linebuf) {
                 // huh, does fgets discard prior data on error like this?
                 // I don't think so....
@@ -63,11 +42,6 @@ char* FAST_FUNC bb_get_chunk_with_continuation(FILE *file, int *end, int *lineno
         return linebuf;
 }
 
-char* FAST_FUNC bb_get_chunk_from_file(FILE *file, int *end)
-{
-        return bb_get_chunk_with_continuation(file, end, NULL);
-}
-
 /* Get line, including trailing \n if any */
 char* FAST_FUNC xmalloc_fgets(FILE *file)
 {
diff --git a/libbb/parse_config.c b/libbb/parse_config.c
index 4b0236028..769ae5103 100644
--- a/libbb/parse_config.c
+++ b/libbb/parse_config.c
@@ -104,6 +104,44 @@ void FAST_FUNC config_close(parser_t *parser)
         }
 }
 
+/* This function reads an entire line from a text file, up to a newline
+ * or NUL byte, exclusive.  It returns a malloc'ed char*.
+ * *lineno is incremented for each line.
+ * Trailing '\' is recognized as line continuation.
+ * Returns NULL if EOF/error.
+ */
+static char* get_line_with_continuation(FILE *file, int *lineno)
+{
+        int ch;
+        unsigned idx = 0;
+        char *linebuf = NULL;
+
+        while ((ch = getc(file)) != EOF) {
+                /* grow the line buffer as necessary */
+                if (!(idx & 0xff))
+                        linebuf = xrealloc(linebuf, idx + 0x101);
+                if (ch == '\n')
+                        ch = '\0';
+                linebuf[idx] = (char) ch;
+                if (ch == '\0') {
+                        (*lineno)++;
+                        if (idx == 0 || linebuf[idx-1] != '\\')
+                                break;
+                        idx--; /* go back to '/' */
+                        continue;
+                }
+                idx++;
+        }
+        if (ch == EOF) {
+                /* handle corner case when the file is not ended with '\n' */
+                (*lineno)++;
+                if (linebuf)
+                        linebuf[idx] = '\0';
+        }
+        return linebuf;
+}
+
+
 /*
 0. If parser is NULL return 0.
 1. Read a line from config file. If nothing to read then return 0.
@@ -132,28 +170,24 @@ int FAST_FUNC config_read(parser_t *parser, char **tokens, unsigned flags, const
 {
         char *line;
         int ntokens, mintokens;
-        int t, len;
+        int t;
+
+        if (!parser)
+                return 0;
 
         ntokens = (uint8_t)flags;
         mintokens = (uint8_t)(flags >> 8);
 
-        if (parser == NULL)
-                return 0;
-
 again:
         memset(tokens, 0, sizeof(tokens[0]) * ntokens);
         config_free_data(parser);
 
         /* Read one line (handling continuations with backslash) */
-        line = bb_get_chunk_with_continuation(parser->fp, &len, &parser->lineno);
+        line = get_line_with_continuation(parser->fp, &parser->lineno);
         if (line == NULL)
                 return 0;
         parser->line = line;
 
-        /* Strip trailing line-feed if any */
-        if (len && line[len-1] == '\n')
-                line[len-1] = '\0';
-
         /* Skip token in the start of line? */
         if (flags & PARSE_TRIM)
                 line += strspn(line, delims + 1);