jiffies.h: new header, time_before etc, only

This is a subset of <linux/jiffies.h> with typecheck from <linux/typecheck.h>. Signed-off-by: Alessandro Rubini <rubini@gnudd.com>

jiffies.h: new header, time_before etc, only
This is a subset of <linux/jiffies.h> with typecheck from <linux/typecheck.h>. Signed-off-by: Alessandro Rubini <rubini@gnudd.com>
fec90f15 · Alessandro Rubini · 0d0b81bb · fec90f15
Commit fec90f15 authored Mar 01, 2013 by Alessandro Rubini
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jiffies.h include/ppsi/jiffies.h +40 -0

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--- a/include/ppsi/jiffies.h
+++ b/include/ppsi/jiffies.h
+#ifndef _LINUX_JIFFIES_H
+#define _LINUX_JIFFIES_H
+
+/*
+ * Check at compile time that something is of a particular type.
+ * Always evaluates to 1 so you may use it easily in comparisons.
+ */
+#define typecheck(type,x) \
+({      type __dummy; \
+        typeof(x) __dummy2; \
+         (void)(&__dummy == &__dummy2); \
+        1; \
+})
+
+/*
+ *	These inlines deal with timer wrapping correctly. You are 
+ *	strongly encouraged to use them
+ *	1. Because people otherwise forget
+ *	2. Because if the timer wrap changes in future you won't have to
+ *	   alter your driver code.
+ *
+ * time_after(a,b) returns true if the time a is after time b.
+ *
+ * Do this with "<0" and ">=0" to only test the sign of the result. A
+ * good compiler would generate better code (and a really good compiler
+ * wouldn't care). Gcc is currently neither.
+ */
+#define time_after(a,b)		\
+	(typecheck(unsigned long, a) && \
+	 typecheck(unsigned long, b) && \
+	 ((long)(b) - (long)(a) < 0))
+#define time_before(a,b)	time_after(b,a)
+
+#define time_after_eq(a,b)	\
+	(typecheck(unsigned long, a) && \
+	 typecheck(unsigned long, b) && \
+	 ((long)(a) - (long)(b) >= 0))
+#define time_before_eq(a,b)	time_after_eq(b,a)
+
+#endif