Audit nice(1)

1) val is sufficient as "int" (read the standard)
2) BUGFIX: If getpriority fails, it returns -1 and sets errno.
   Previously, it would correctly catch the errno but not take
   care of the fact that by then val has been decremented by 1.
   Only change val if the getpriority-call has been successful.
3) Add LIMIT()-macro from st to increase readability.
4) setpriority returns < 0 on failure
5) Remove bikeshedding-comment. Read the standard if you wonder.
6) return-value trick from env(1)

README

@@ -47,7 +47,7 @@ The following tools are implemented ('*' == finished, '#' == UTF-8 support,
 =*  mkfifo          yes                          none
 =*  mktemp          non-posix                    none
 =*  mv              yes                          none (-i)
-=*  nice            yes                          none
+=*| nice            yes                          none
 =   nl              no                           -d, -f, -h, -l, -p
 =*  nohup           yes                          none
 #*  paste           yes                          none

nice.1

@@ -1,4 +1,4 @@
-.Dd January 28, 2015
+.Dd March 1, 2015
 .Dt NICE 1
 .Os sbase
 .Sh NAME
@@ -25,7 +25,7 @@ ranging from
 .Sy -20
 (highest priority)
 to
-.Sy +19
+.Sy +20
 (lowest priority).
 Default is 10.
 .El

nice.c

@@ -16,8 +16,7 @@ usage(void)
 int
 main(int argc, char *argv[])
 {
-	long val = 10;
-	int savederrno;
+	int val = 10, r, savederrno;
 
 	ARGBEGIN {
 	case 'n':
@@ -28,20 +27,22 @@ main(int argc, char *argv[])
 		break;
 	} ARGEND;
 
-	if (argc == 0)
+	if (!argc)
 		usage();
 
 	errno = 0;
-	val += getpriority(PRIO_PROCESS, 0);
-	if (errno != 0)
+	r = getpriority(PRIO_PROCESS, 0);
+	if (errno)
 		weprintf("getpriority:");
-	val = MAX(PRIO_MIN, MIN(val, PRIO_MAX));
-	if (setpriority(PRIO_PROCESS, 0, val) != 0)
+	else
+		val += r;
+	LIMIT(val, PRIO_MIN, PRIO_MAX);
+	if (setpriority(PRIO_PROCESS, 0, val) < 0)
 		weprintf("setpriority:");
 
-	/* POSIX specifies the nice failure still invokes the command */
 	execvp(argv[0], argv);
 	savederrno = errno;
 	weprintf("execvp %s:", argv[0]);
-	return (savederrno == ENOENT)? 127 : 126;
+
+	return 126 + (savederrno == ENOENT);
 }

util.h

@@ -13,6 +13,8 @@
 #define MIN(x,y)  ((x) < (y) ? (x) : (y))
 #undef MAX
 #define MAX(x,y)  ((x) > (y) ? (x) : (y))
+#undef LIMIT
+#define LIMIT(x, a, b)  (x) = (x) < (a) ? (a) : (x) > (b) ? (b) : (x)
 
 #define LEN(x) (sizeof (x) / sizeof *(x))