less: improvements to verbose status messages

Make verbose status messages (-m/-M flags) behave more like the
real `less` command:

- fix display of line numbers so they're correct whether lines are
  being truncated (-S flag) or wrapped.
- don't display total lines or percentage when lines are read from
  stdin:  we don't have that information until we reach EOF.  When
  we do reach EOF the additional information is displayed.
- when lines are read from a file count the total number of lines
  so that we can display percentages.  Counting lines is avoided
  until the information is actually needed.  If the user pages to
  EOF the separate read pass can be avoided entirely.

Fixes Bug 7586

function                                             old     new   delta
m_status_print                                       195     382    +187
safe_lineno                                            -      35     +35
reinitialize                                         172     182     +10
read_lines                                           675     685     +10
buffer_fill_and_print                                178     169      -9
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 3/1 up/down: 242/-9)            Total: 233 bytes

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 69 insertions, 14 deletions

diff --git a/miscutils/less.c b/miscutils/less.c
index 90c103888..dd932c5ed 100644
--- a/miscutils/less.c
+++ b/miscutils/less.c
@@ -165,6 +165,11 @@ enum {
 enum { pattern_valid = 0 };
 #endif
 
+enum {
+        READING_FILE = -1,
+        READING_STDIN = -2
+};
+
 struct globals {
         int cur_fline; /* signed */
         int kbd_fd;  /* fd to get input from */
@@ -188,6 +193,9 @@ struct globals {
         unsigned current_file;
         char *filename;
         char **files;
+#if ENABLE_FEATURE_LESS_FLAGS
+        int num_lines; /* input source if < 0, line count if >= 0 */
+#endif
 #if ENABLE_FEATURE_LESS_MARKS
         unsigned num_marks;
         unsigned mark_lines[15][2];
@@ -229,6 +237,7 @@ struct globals {
 #define current_file        (G.current_file      )
 #define filename            (G.filename          )
 #define files               (G.files             )
+#define num_lines           (G.num_lines         )
 #define num_marks           (G.num_marks         )
 #define mark_lines          (G.mark_lines        )
 #if ENABLE_FEATURE_LESS_REGEXP
@@ -574,6 +583,10 @@ static void read_lines(void)
                         print_statusline(bb_msg_read_error);
                 }
         }
+#if ENABLE_FEATURE_LESS_FLAGS
+        else if (eof_error == 0)
+                num_lines = max_lineno;
+#endif
 
         fill_match_lines(old_max_fline);
 #if ENABLE_FEATURE_LESS_REGEXP
@@ -584,18 +597,23 @@ static void read_lines(void)
 }
 
 #if ENABLE_FEATURE_LESS_FLAGS
-/* Interestingly, writing calc_percent as a function saves around 32 bytes
- * on my build. */
-static int calc_percent(void)
+static int safe_lineno(int fline)
 {
-        unsigned p = (100 * (cur_fline+max_displayed_line+1) + max_fline/2) / (max_fline+1);
-        return p <= 100 ? p : 100;
+        if (fline >= max_fline)
+                fline = max_fline - 1;
+
+        /* also catches empty file (max_fline == 0) */
+        if (fline < 0)
+                return 0;
+
+        return LINENO(flines[fline]) + 1;
 }
 
 /* Print a status line if -M was specified */
 static void m_status_print(void)
 {
-        int percentage;
+        int first, last;
+        unsigned percent;
 
         if (less_gets_pos >= 0) /* don't touch statusline while input is done! */
                 return;
@@ -604,17 +622,51 @@ static void m_status_print(void)
         printf(HIGHLIGHT"%s", filename);
         if (num_files > 1)
                 printf(" (file %i of %i)", current_file, num_files);
-        printf(" lines %i-%i/%i ",
-                        cur_fline + 1, cur_fline + max_displayed_line + 1,
-                        max_fline + 1);
+
+        first = safe_lineno(cur_fline);
+        last = (option_mask32 & FLAG_S)
+                        ? MIN(first + max_displayed_line, max_lineno)
+                        : safe_lineno(cur_fline + max_displayed_line);
+        printf(" lines %i-%i", first, last);
+
+        if (num_lines == READING_FILE) {
+                int count, fd;
+                ssize_t len, i;
+                char buf[4096];
+                struct stat stbuf;
+
+                /* count number of lines in file */
+                count = 0;
+                fd = open(filename, O_RDONLY);
+                if (fd < 0)
+                        goto skip;
+                if (fstat(fd, &stbuf) != 0 || !S_ISREG(stbuf.st_mode))
+                        goto do_close;
+                while ((len = safe_read(fd, buf, sizeof(buf))) > 0) {
+                        for (i = 0; i < len; ++i) {
+                                if (buf[i] == '\n' && ++count == MAXLINES)
+                                        goto done;
+                        }
+                }
+ done:
+                num_lines = count;
+ do_close:
+                close(fd);
+ skip: ;
+        }
+
+        if (num_lines >= 0)
+                printf("/%i", num_lines);
+
         if (cur_fline >= (int)(max_fline - max_displayed_line)) {
-                printf("(END)"NORMAL);
+                printf(" (END)");
                 if (num_files > 1 && current_file != num_files)
-                        printf(HIGHLIGHT" - next: %s"NORMAL, files[current_file]);
-                return;
+                        printf(" - next: %s", files[current_file]);
+        } else if (num_lines > 0) {
+                percent = (100 * last + num_lines/2) / num_lines;
+                printf(" %i%%", percent <= 100 ? percent : 100);
         }
-        percentage = calc_percent();
-        printf("%i%%"NORMAL, percentage);
+        printf(NORMAL);
 }
 #endif
 
@@ -915,6 +967,9 @@ static void reinitialize(void)
         max_fline = -1;
         cur_fline = 0;
         max_lineno = 0;
+#if ENABLE_FEATURE_LESS_FLAGS
+        num_lines = filename ? READING_FILE : READING_STDIN;
+#endif
         open_file_and_read_lines();
 #if ENABLE_FEATURE_LESS_ASK_TERMINAL
         if (G.winsize_err)