unexpand: fix incorrect expansion, add test for it

function                                             old     new   delta
expand_main                                          676     656     -20

1 files changed, 27 insertions, 39 deletions

diff --git a/coreutils/expand.c b/coreutils/expand.c
index 3ca7e5c29..0967e2534 100644
--- a/coreutils/expand.c
+++ b/coreutils/expand.c
@@ -68,51 +68,39 @@ static void expand(FILE *file, int tab_size, unsigned opt)
 static void unexpand(FILE *file, unsigned tab_size, unsigned opt)
 {
         char *line;
-        char *ptr;
-        int convert;
-        int pos;
-        int i = 0;
-        unsigned column = 0;
 
         while ((line = xmalloc_fgets(file)) != NULL) {
-                convert = 1;
-                pos = 0;
-                ptr = line;
-                while (*line) {
-                        while ((*line == ' ' || *line == '\t') && convert) {
-                                pos += (*line == ' ') ? 1 : tab_size;
-                                line++;
+                char *ptr = line;
+                unsigned column = 0;
+
+                while (*ptr) {
+                        unsigned n;
+
+                        while (*ptr == ' ') {
                                 column++;
-                                if ((opt & OPT_ALL) && column == tab_size) {
-                                        column = 0;
-                                        goto put_tab;
-                                }
+                                ptr++;
+                        }
+                        if (*ptr == '\t') {
+                                column += tab_size - (column % tab_size);
+                                ptr++;
+                                continue;
                         }
-                        if (pos) {
-                                i = pos / tab_size;
-                                if (i) {
-                                        for (; i > 0; i--) {
- put_tab:
-                                                bb_putchar('\t');
-                                        }
-                                } else {
-                                        for (i = pos % tab_size; i > 0; i--) {
-                                                bb_putchar(' ');
-                                        }
-                                }
-                                pos = 0;
-                        } else {
-                                if (opt & OPT_INITIAL) {
-                                        convert = 0;
-                                }
-                                if (opt & OPT_ALL) {
-                                        column++;
-                                }
-                                bb_putchar(*line);
-                                line++;
+
+                        n = column / tab_size;
+                        column = column % tab_size;
+                        while (n--)
+                                putchar('\t');
+
+                        if ((opt & OPT_INITIAL) && ptr != line) {
+                                printf("%*s%s", column, "", ptr);
+                                break;
                         }
+                        n = strcspn(ptr, "\t ");
+                        printf("%*s%.*s", column, "", n, ptr);
+                        ptr += n;
+                        column = (column + n) % tab_size;
                 }
-                free(ptr);
+                free(line);
         }
 }
 #endif