usr: sort, cmp, strings, du, time

- sort [-r] [-n]: everything in RAM, which bounds it - a task has 8 KiB and a
  file caps at 3 KiB, so 96 lines of 2400 bytes with room for the stack.
  Insertion sort over an index; at that size the simple thing is fast and
  costs far less ROM. `uniq -c f | sort -n -r` finally works.
  NB the key needs a scratch SLOT of its own: gt() compares table entries, so
  reusing slot i as scratch overwrites the entries being shifted into it.
- cmp: reports the first differing byte, silent when the files match. There
  was no way to check a copy on the machine - you had to haul both to a host.
- strings [-n N]: pairs with xxd now that /bin/<prog> is readable. It finds
  "gbos sm83 (Game Boy Color)" inside /bin/uname.
- du [dir]: 256-byte blocks, the unit df and the filesystem use. Bytes
  overflow - /bin alone is 52 x 16 KiB, which wrapped a 16-bit counter and
  printed 32768. Recurses by re-opendir'ing, since the kernel keeps only one
  "directory being listed" cursor.
- time CMD: 1/64 s resolution from the tick counter. It rebuilds the child's
  command line at $A000 - which is its own argument area, so everything is
  copied to the stack first.

1 files changed, 61 insertions, 0 deletions

diff --git a/usr/cmp.c b/usr/cmp.c
new file mode 100644
index 0000000..5a4a718
--- /dev/null
+++ b/usr/cmp.c
@@ -0,0 +1,61 @@
+#include "gbos.h"
+/* cmp FILE1 FILE2: report the first byte where two files differ, or say
+ * nothing when they match (like cmp(1), silence means identical).
+ *
+ * After cp/mv/tee/nc there was still no way to check a copy ON the machine -
+ * you had to haul both files to a host. */
+void main(void) {
+    char *argv[4];
+    unsigned char argc = argv_parse(argv, 4);
+    unsigned char a, b;
+    unsigned int off = 0;
+    int ca, cb;
+
+    if (argc < 2) {
+        puts("usage: cmp FILE1 FILE2");
+        nl();
+        sexit(2);
+    }
+    a = open(argv[0], O_READ);
+    if (a > 3) {
+        puts("cmp: cannot open ");
+        puts(argv[0]);
+        nl();
+        sexit(2);
+    }
+    b = open(argv[1], O_READ);
+    if (b > 3) {
+        puts("cmp: cannot open ");
+        puts(argv[1]);
+        nl();
+        close(a);
+        sexit(2);
+    }
+
+    for (;;) {
+        ca = fgetc(a);
+        cb = fgetc(b);
+        if (ca < 0 && cb < 0) break; /* same length, same bytes */
+        if (ca < 0 || cb < 0) {
+            puts("cmp: EOF on ");
+            puts(ca < 0 ? argv[0] : argv[1]);
+            puts(" after ");
+            putu(off);
+            nl();
+            close(a);
+            close(b);
+            sexit(1);
+        }
+        if (ca != cb) {
+            puts("differ: byte ");
+            putu(off);
+            nl();
+            close(a);
+            close(b);
+            sexit(1);
+        }
+        off++;
+    }
+    close(a);
+    close(b);
+}