sort: fix -s. Closes 10671

function                                             old     new   delta
sort_main                                            786     862     +76
compare_keys                                         720     794     +74
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 150/0)             Total: 150 bytes

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

diff --git a/coreutils/sort.c b/coreutils/sort.c
index ceea24491c90bf424bae926be1187859521f0e6b..8ffd0cf44198754eeb4762bfe8970128d6b272cd 100644 (file)
--- a/coreutils/sort.c
+++ b/coreutils/sort.c
@@ -62,9 +62,9 @@
 //usage:     "\n       -u      Suppress duplicate lines"
 //usage:       IF_FEATURE_SORT_BIG(
 //usage:     "\n       -z      Lines are terminated by NUL, not newline"
-////usage:     "\n     -m      Ignored for GNU compatibility"
-////usage:     "\n     -S BUFSZ Ignored for GNU compatibility"
-////usage:     "\n     -T TMPDIR Ignored for GNU compatibility"
+///////:     "\n       -m      Ignored for GNU compatibility"
+///////:     "\n       -S BUFSZ Ignored for GNU compatibility"
+///////:     "\n       -T TMPDIR Ignored for GNU compatibility"
 //usage:       )
 //usage:
 //usage:#define sort_example_usage
@@ -117,6 +117,7 @@ enum {
        FLAG_k  = 0x10000,
        FLAG_t  = 0x20000,
        FLAG_bb = 0x80000000,   /* Ignore trailing blanks  */
+       FLAG_no_tie_break = 0x40000000,
 };
 
 #if ENABLE_FEATURE_SORT_BIG
@@ -340,10 +341,34 @@ static int compare_keys(const void *xarg, const void *yarg)
 #endif
        } /* for */
 
-       /* Perform fallback sort if necessary */
-       if (!retval && !(option_mask32 & FLAG_s)) {
-               flags = option_mask32;
-               retval = strcmp(*(char **)xarg, *(char **)yarg);
+       if (retval == 0) {
+               /* So far lines are "the same" */
+
+               if (option_mask32 & FLAG_s) {
+                       /* "Stable sort": later line is "smaller",
+                        * IOW: do not allow qsort() to swap equal lines.
+                        */
+                       uint32_t *p32;
+                       uint32_t x32, y32;
+                       char *line;
+                       unsigned len;
+
+                       line = *(char**)xarg;
+                       len = (strlen(line) + 4) & (~3u);
+                       p32 = (void*)(line + len);
+                       x32 = *p32;
+                       line = *(char**)yarg;
+                       len = (strlen(line) + 4) & (~3u);
+                       p32 = (void*)(line + len);
+                       y32 = *p32;
+
+                       retval = x32 > y32;
+               } else
+               if (!(option_mask32 & FLAG_no_tie_break)) {
+                       /* fallback sort */
+                       flags = option_mask32;
+                       retval = strcmp(*(char **)xarg, *(char **)yarg);
+               }
        }
 
        if (flags & FLAG_r)
@@ -368,7 +393,7 @@ static unsigned str2u(char **str)
 int sort_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int sort_main(int argc UNUSED_PARAM, char **argv)
 {
-       char *line, **lines;
+       char **lines;
        char *str_ignored, *str_o, *str_t;
        llist_t *lst_k = NULL;
        int i;
@@ -457,7 +482,7 @@ int sort_main(int argc UNUSED_PARAM, char **argv)
                 * do not continue to next file: */
                FILE *fp = xfopen_stdin(*argv);
                for (;;) {
-                       line = GET_LINE(fp);
+                       char *line = GET_LINE(fp);
                        if (!line)
                                break;
                        lines = xrealloc_vector(lines, 6, linecount);
@@ -482,15 +507,35 @@ int sort_main(int argc UNUSED_PARAM, char **argv)
                return EXIT_SUCCESS;
        }
 #endif
+
+       /* For stable sort, store original line position beyond terminating NUL */
+       if (option_mask32 & FLAG_s) {
+               for (i = 0; i < linecount; i++) {
+                       uint32_t *p32;
+                       char *line;
+                       unsigned len;
+
+                       line = lines[i];
+                       len = (strlen(line) + 4) & (~3u);
+                       lines[i] = line = xrealloc(line, len + 4);
+                       p32 = (void*)(line + len);
+                       *p32 = i;
+               }
+               /*option_mask32 |= FLAG_no_tie_break;*/
+               /* ^^^redundant: if FLAG_s, compare_keys() does no tie break */
+       }
+
        /* Perform the actual sort */
        qsort(lines, linecount, sizeof(lines[0]), compare_keys);
 
        /* Handle -u */
        if (option_mask32 & FLAG_u) {
                int j = 0;
-               /* coreutils 6.3 drop lines for which only key is the same */
-               /* -- disabling last-resort compare... */
-               option_mask32 |= FLAG_s;
+               /* coreutils 6.3 drop lines for which only key is the same
+                * -- disabling last-resort compare, or else compare_keys()
+                * will be the same only for completely identical lines.
+                */
+               option_mask32 |= FLAG_no_tie_break;
                for (i = 1; i < linecount; i++) {
                        if (compare_keys(&lines[j], &lines[i]) == 0)
                                free(lines[i]);