cmp: add support for -n

Add support to for "-n" to cmp in order to compare at most n bytes.

function                                             old     new   delta
cmp_main                                             552     589     +37
.rodata                                           104198  104203      +5
packed_usage                                       34102   34074     -28
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/1 up/down: 42/-28)             Total: 14 bytes

Signed-off-by: Walter Lozano <walter.lozano@collabora.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 10 insertions, 4 deletions

diff --git a/editors/cmp.c b/editors/cmp.c
index e106d814e..9eaff2b8e 100644
--- a/editors/cmp.c
+++ b/editors/cmp.c
@@ -18,12 +18,13 @@
 //kbuild:lib-$(CONFIG_CMP) += cmp.o
 
 //usage:#define cmp_trivial_usage
-//usage:       "[-ls] FILE1 [FILE2" IF_DESKTOP(" [SKIP1 [SKIP2]]") "]"
+//usage:       "[-ls] [-n NUM] FILE1 [FILE2" IF_DESKTOP(" [SKIP1 [SKIP2]]") "]"
 //usage:#define cmp_full_usage "\n\n"
 //usage:       "Compare FILE1 with FILE2 (or stdin)\n"
 //usage:     "\n	-l	Write the byte numbers (decimal) and values (octal)"
 //usage:     "\n		for all differing bytes"
 //usage:     "\n	-s	Quiet"
+//usage:     "\n	-n NUM	Compare at most NUM bytes"
 
 /* BB_AUDIT SUSv3 (virtually) compliant -- uses nicer GNU format for -l. */
 /* http://www.opengroup.org/onlinepubs/007904975/utilities/cmp.html */
@@ -35,9 +36,10 @@ static const char fmt_differ[] ALIGN1 = "%s %s differ: char %"OFF_FMT"u, line %u
 // This fmt_l_opt uses gnu-isms.  SUSv3 would be "%.0s%.0s%"OFF_FMT"u %o %o\n"
 static const char fmt_l_opt[] ALIGN1 = "%.0s%.0s%"OFF_FMT"u %3o %3o\n";
 
-#define OPT_STR "sl"
+#define OPT_STR "sln:"
 #define CMP_OPT_s (1<<0)
 #define CMP_OPT_l (1<<1)
+#define CMP_OPT_n (1<<2)
 
 int cmp_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int cmp_main(int argc UNUSED_PARAM, char **argv)
@@ -50,13 +52,15 @@ int cmp_main(int argc UNUSED_PARAM, char **argv)
 	int c1, c2;
 	unsigned opt;
 	int retval = 0;
+	int max_count = -1;
 
 	opt = getopt32(argv, "^"
 			OPT_STR
-			"\0" "-1"
+			"\0" "-1:n+"
 			IF_DESKTOP(":?4")
 			IF_NOT_DESKTOP(":?2")
-			":l--s:s--l"
+			":l--s:s--l",
+			&max_count
 	);
 	argv += optind;
 
@@ -95,6 +99,8 @@ int cmp_main(int argc UNUSED_PARAM, char **argv)
 		while (skip2) { getc(fp2); skip2--; }
 	}
 	do {
+		if (max_count >= 0 && --max_count < 0)
+			break;
 		c1 = getc(fp1);
 		c2 = getc(fp2);
 		++char_pos;