cmp: accept SI suffixes for skip1 and skip2

This is compatible with GNU cmp.

Reviewed by:	bapt (earlier version), markj, imp
Sponsored by:	Klara, Inc.
Differential Revision:	https://reviews.freebsd.org/D32071

usr.bin/cmp/Makefile

@@ -6,6 +6,8 @@
 PROG=	cmp
 SRCS=	cmp.c link.c misc.c regular.c special.c
 
+LIBADD=	util
+
 HAS_TESTS=
 SUBDIR.${MK_TESTS}+= tests
 

usr.bin/cmp/cmp.1

@@ -31,7 +31,7 @@
 .\"     @(#)cmp.1	8.1 (Berkeley) 6/6/93
 .\" $FreeBSD$
 .\"
-.Dd June 20, 2020
+.Dd September 23, 2021
 .Dt CMP 1
 .Os
 .Sh NAME
@@ -86,6 +86,11 @@ and
 respectively, where the comparison will begin.
 The offset is decimal by default, but may be expressed as a hexadecimal
 or octal value by preceding it with a leading ``0x'' or ``0''.
+.Pp
+.Ar skip1
+and
+.Ar skip2
+may also be specified with SI size suffixes.
 .Sh EXIT STATUS
 The
 .Nm
@@ -164,8 +169,17 @@ The
 and
 .Fl z
 options are extensions to the standard.
+.Ar skip1
+and
+.Ar skip2
+arguments are extensions to the standard.
 .Sh HISTORY
 A
 .Nm
 command appeared in
 .At v1 .
+.Sh BUGS
+The phrase
+.Dq SI size suffixes
+above refers to the traditional power of two convention, as described in
+.Xr expand_number 3 .

usr.bin/cmp/cmp.c

@@ -58,6 +58,8 @@ __FBSDID("$FreeBSD$");
 #include <string.h>
 #include <unistd.h>
 
+#include <libutil.h>
+
 #include "extern.h"
 
 bool	lflag, sflag, xflag, zflag;
@@ -81,6 +83,7 @@ main(int argc, char *argv[])
 	bool special;
 	const char *file1, *file2;
 
+	skip1 = skip2 = 0;
 	oflag = O_RDONLY;
 	while ((ch = getopt_long(argc, argv, "+hlsxz", long_opts, NULL)) != -1)
 		switch (ch) {
@@ -145,8 +148,15 @@ main(int argc, char *argv[])
 			exit(ERR_EXIT);
 	}
 
-	skip1 = argc > 2 ? strtol(argv[2], NULL, 0) : 0;
-	skip2 = argc == 4 ? strtol(argv[3], NULL, 0) : 0;
+	if (argc > 2 && expand_number(argv[2], &skip1) < 0) {
+		fprintf(stderr, "Invalid skip1: %s\n", argv[2]);
+		usage();
+	}
+
+	if (argc == 4 && expand_number(argv[3], &skip2) < 0) {
+		fprintf(stderr, "Invalid skip2: %s\n", argv[3]);
+		usage();
+	}
 
 	if (sflag && skip1 == 0 && skip2 == 0)
 		zflag = true;

usr.bin/cmp/tests/cmp_test2.sh

@@ -75,9 +75,26 @@ pr252542_body()
 	atf_check -s exit:1 -o ignore cmp -z a b 4 3
 }
 
+atf_test_case skipsuff
+skipsuff_head()
+{
+	atf_set "descr" "Test cmp(1) accepting SI suffixes on skips"
+}
+skipsuff_body()
+{
+
+	jot -nb a -s '' 1028 > a
+	jot -nb b -s '' 1024 > b
+	jot -nb a -s '' 4 >> b
+
+	atf_check -s exit:1 -o ignore cmp -s a b
+	atf_check -s exit:0 cmp -s a b 1k 1k
+}
+
 atf_init_test_cases()
 {
 	atf_add_test_case special
 	atf_add_test_case symlink
 	atf_add_test_case pr252542
+	atf_add_test_case skipsuff
 }