#ifndef _LINUX_JIFFIES_H
  #define _LINUX_JIFFIES_H
  
  #include <linux/math64.h>
  #include <linux/kernel.h>
  #include <linux/types.h>
  #include <linux/time.h>
  #include <linux/timex.h>
  #include <asm/param.h>			/* for HZ */
  
  /*
   * The following defines establish the engineering parameters of the PLL
   * model. The HZ variable establishes the timer interrupt frequency, 100 Hz
   * for the SunOS kernel, 256 Hz for the Ultrix kernel and 1024 Hz for the
   * OSF/1 kernel. The SHIFT_HZ define expresses the same value as the
   * nearest power of two in order to avoid hardware multiply operations.
   */
  #if HZ >= 12 && HZ < 24
  # define SHIFT_HZ	4
  #elif HZ >= 24 && HZ < 48
  # define SHIFT_HZ	5
  #elif HZ >= 48 && HZ < 96
  # define SHIFT_HZ	6
  #elif HZ >= 96 && HZ < 192
  # define SHIFT_HZ	7
  #elif HZ >= 192 && HZ < 384
  # define SHIFT_HZ	8
  #elif HZ >= 384 && HZ < 768
  # define SHIFT_HZ	9
  #elif HZ >= 768 && HZ < 1536
  # define SHIFT_HZ	10
  #elif HZ >= 1536 && HZ < 3072
  # define SHIFT_HZ	11
  #elif HZ >= 3072 && HZ < 6144
  # define SHIFT_HZ	12
  #elif HZ >= 6144 && HZ < 12288
  # define SHIFT_HZ	13
  #else
  # error Invalid value of HZ.
  #endif
  
  /* Suppose we want to divide two numbers NOM and DEN: NOM/DEN, then we can
   * improve accuracy by shifting LSH bits, hence calculating:
   *     (NOM << LSH) / DEN
   * This however means trouble for large NOM, because (NOM << LSH) may no
   * longer fit in 32 bits. The following way of calculating this gives us
   * some slack, under the following conditions:
   *   - (NOM / DEN) fits in (32 - LSH) bits.
   *   - (NOM % DEN) fits in (32 - LSH) bits.
   */
  #define SH_DIV(NOM,DEN,LSH) (   (((NOM) / (DEN)) << (LSH))              \
                               + ((((NOM) % (DEN)) << (LSH)) + (DEN) / 2) / (DEN))
  
  /* LATCH is used in the interval timer and ftape setup. */
  #define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ)	/* For divider */
  
  extern int register_refined_jiffies(long clock_tick_rate);
  
  /* TICK_NSEC is the time between ticks in nsec assuming SHIFTED_HZ */
  #define TICK_NSEC ((NSEC_PER_SEC+HZ/2)/HZ)
  
  /* TICK_USEC is the time between ticks in usec assuming fake USER_HZ */
  #define TICK_USEC ((1000000UL + USER_HZ/2) / USER_HZ)
  
  /* some arch's have a small-data section that can be accessed register-relative
   * but that can only take up to, say, 4-byte variables. jiffies being part of
   * an 8-byte variable may not be correctly accessed unless we force the issue
   */
  #define __jiffy_data  __attribute__((section(".data")))
  
  /*
   * The 64-bit value is not atomic - you MUST NOT read it
   * without sampling the sequence number in jiffies_lock.
   * get_jiffies_64() will do this for you as appropriate.
   */
  extern u64 __jiffy_data jiffies_64;
  extern unsigned long volatile __jiffy_data jiffies;
  
  #if (BITS_PER_LONG < 64)
  u64 get_jiffies_64(void);
  #else
  static inline u64 get_jiffies_64(void)
  {
  	return (u64)jiffies;
  }
  #endif
  
  /*
   *	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) - (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) - (b)) >= 0))
  #define time_before_eq(a,b)	time_after_eq(b,a)
  
  /*
   * Calculate whether a is in the range of [b, c].
   */
  #define time_in_range(a,b,c) \
  	(time_after_eq(a,b) && \
  	 time_before_eq(a,c))
  
  /*
   * Calculate whether a is in the range of [b, c).
   */
  #define time_in_range_open(a,b,c) \
  	(time_after_eq(a,b) && \
  	 time_before(a,c))
  
  /* Same as above, but does so with platform independent 64bit types.
   * These must be used when utilizing jiffies_64 (i.e. return value of
   * get_jiffies_64() */
  #define time_after64(a,b)	\
  	(typecheck(__u64, a) &&	\
  	 typecheck(__u64, b) && \
  	 ((__s64)((b) - (a)) < 0))
  #define time_before64(a,b)	time_after64(b,a)
  
  #define time_after_eq64(a,b)	\
  	(typecheck(__u64, a) && \
  	 typecheck(__u64, b) && \
  	 ((__s64)((a) - (b)) >= 0))
  #define time_before_eq64(a,b)	time_after_eq64(b,a)
  
  #define time_in_range64(a, b, c) \
  	(time_after_eq64(a, b) && \
  	 time_before_eq64(a, c))
  
  /*
   * These four macros compare jiffies and 'a' for convenience.
   */
  
  /* time_is_before_jiffies(a) return true if a is before jiffies */
  #define time_is_before_jiffies(a) time_after(jiffies, a)
  
  /* time_is_after_jiffies(a) return true if a is after jiffies */
  #define time_is_after_jiffies(a) time_before(jiffies, a)
  
  /* time_is_before_eq_jiffies(a) return true if a is before or equal to jiffies*/
  #define time_is_before_eq_jiffies(a) time_after_eq(jiffies, a)
  
  /* time_is_after_eq_jiffies(a) return true if a is after or equal to jiffies*/
  #define time_is_after_eq_jiffies(a) time_before_eq(jiffies, a)
  
  /*
   * Have the 32 bit jiffies value wrap 5 minutes after boot
   * so jiffies wrap bugs show up earlier.
   */
  #define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ))
  
  /*
   * Change timeval to jiffies, trying to avoid the
   * most obvious overflows..
   *
   * And some not so obvious.
   *
   * Note that we don't want to return LONG_MAX, because
   * for various timeout reasons we often end up having
   * to wait "jiffies+1" in order to guarantee that we wait
   * at _least_ "jiffies" - so "jiffies+1" had better still
   * be positive.
   */
  #define MAX_JIFFY_OFFSET ((LONG_MAX >> 1)-1)
  
  extern unsigned long preset_lpj;
  
  /*
   * We want to do realistic conversions of time so we need to use the same
   * values the update wall clock code uses as the jiffies size.  This value
   * is: TICK_NSEC (which is defined in timex.h).  This
   * is a constant and is in nanoseconds.  We will use scaled math
   * with a set of scales defined here as SEC_JIFFIE_SC,  USEC_JIFFIE_SC and
   * NSEC_JIFFIE_SC.  Note that these defines contain nothing but
   * constants and so are computed at compile time.  SHIFT_HZ (computed in
   * timex.h) adjusts the scaling for different HZ values.
  
   * Scaled math???  What is that?
   *
   * Scaled math is a way to do integer math on values that would,
   * otherwise, either overflow, underflow, or cause undesired div
   * instructions to appear in the execution path.  In short, we "scale"
   * up the operands so they take more bits (more precision, less
   * underflow), do the desired operation and then "scale" the result back
   * by the same amount.  If we do the scaling by shifting we avoid the
   * costly mpy and the dastardly div instructions.
  
   * Suppose, for example, we want to convert from seconds to jiffies
   * where jiffies is defined in nanoseconds as NSEC_PER_JIFFIE.  The
   * simple math is: jiff = (sec * NSEC_PER_SEC) / NSEC_PER_JIFFIE; We
   * observe that (NSEC_PER_SEC / NSEC_PER_JIFFIE) is a constant which we
   * might calculate at compile time, however, the result will only have
   * about 3-4 bits of precision (less for smaller values of HZ).
   *
   * So, we scale as follows:
   * jiff = (sec) * (NSEC_PER_SEC / NSEC_PER_JIFFIE);
   * jiff = ((sec) * ((NSEC_PER_SEC * SCALE)/ NSEC_PER_JIFFIE)) / SCALE;
   * Then we make SCALE a power of two so:
   * jiff = ((sec) * ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE)) >> SCALE;
   * Now we define:
   * #define SEC_CONV = ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE))
   * jiff = (sec * SEC_CONV) >> SCALE;
   *
   * Often the math we use will expand beyond 32-bits so we tell C how to
   * do this and pass the 64-bit result of the mpy through the ">> SCALE"
   * which should take the result back to 32-bits.  We want this expansion
   * to capture as much precision as possible.  At the same time we don't
   * want to overflow so we pick the SCALE to avoid this.  In this file,
   * that means using a different scale for each range of HZ values (as
   * defined in timex.h).
   *
   * For those who want to know, gcc will give a 64-bit result from a "*"
   * operator if the result is a long long AND at least one of the
   * operands is cast to long long (usually just prior to the "*" so as
   * not to confuse it into thinking it really has a 64-bit operand,
   * which, buy the way, it can do, but it takes more code and at least 2
   * mpys).
  
   * We also need to be aware that one second in nanoseconds is only a
   * couple of bits away from overflowing a 32-bit word, so we MUST use
   * 64-bits to get the full range time in nanoseconds.
  
   */
  
  /*
   * Here are the scales we will use.  One for seconds, nanoseconds and
   * microseconds.
   *
   * Within the limits of cpp we do a rough cut at the SEC_JIFFIE_SC and
   * check if the sign bit is set.  If not, we bump the shift count by 1.
   * (Gets an extra bit of precision where we can use it.)
   * We know it is set for HZ = 1024 and HZ = 100 not for 1000.
   * Haven't tested others.
  
   * Limits of cpp (for #if expressions) only long (no long long), but
   * then we only need the most signicant bit.
   */
  
  #define SEC_JIFFIE_SC (31 - SHIFT_HZ)
  #if !((((NSEC_PER_SEC << 2) / TICK_NSEC) << (SEC_JIFFIE_SC - 2)) & 0x80000000)
  #undef SEC_JIFFIE_SC
  #define SEC_JIFFIE_SC (32 - SHIFT_HZ)
  #endif
  #define NSEC_JIFFIE_SC (SEC_JIFFIE_SC + 29)
  #define SEC_CONVERSION ((unsigned long)((((u64)NSEC_PER_SEC << SEC_JIFFIE_SC) +\
                                  TICK_NSEC -1) / (u64)TICK_NSEC))
  
  #define NSEC_CONVERSION ((unsigned long)((((u64)1 << NSEC_JIFFIE_SC) +\
                                          TICK_NSEC -1) / (u64)TICK_NSEC))
  /*
   * The maximum jiffie value is (MAX_INT >> 1).  Here we translate that
   * into seconds.  The 64-bit case will overflow if we are not careful,
   * so use the messy SH_DIV macro to do it.  Still all constants.
   */
  #if BITS_PER_LONG < 64
  # define MAX_SEC_IN_JIFFIES \
  	(long)((u64)((u64)MAX_JIFFY_OFFSET * TICK_NSEC) / NSEC_PER_SEC)
  #else	/* take care of overflow on 64 bits machines */
  # define MAX_SEC_IN_JIFFIES \
  	(SH_DIV((MAX_JIFFY_OFFSET >> SEC_JIFFIE_SC) * TICK_NSEC, NSEC_PER_SEC, 1) - 1)
  
  #endif
  
  /*
   * Convert various time units to each other:
   */
  extern unsigned int jiffies_to_msecs(const unsigned long j);
  extern unsigned int jiffies_to_usecs(const unsigned long j);
  
  static inline u64 jiffies_to_nsecs(const unsigned long j)
  {
  	return (u64)jiffies_to_usecs(j) * NSEC_PER_USEC;
  }
  
  extern unsigned long msecs_to_jiffies(const unsigned int m);
  extern unsigned long usecs_to_jiffies(const unsigned int u);
  extern unsigned long timespec_to_jiffies(const struct timespec *value);
  extern void jiffies_to_timespec(const unsigned long jiffies,
  				struct timespec *value);
  extern unsigned long timeval_to_jiffies(const struct timeval *value);
  extern void jiffies_to_timeval(const unsigned long jiffies,
  			       struct timeval *value);
  
  extern clock_t jiffies_to_clock_t(unsigned long x);
  static inline clock_t jiffies_delta_to_clock_t(long delta)
  {
  	return jiffies_to_clock_t(max(0L, delta));
  }
  
  extern unsigned long clock_t_to_jiffies(unsigned long x);
  extern u64 jiffies_64_to_clock_t(u64 x);
  extern u64 nsec_to_clock_t(u64 x);
  extern u64 nsecs_to_jiffies64(u64 n);
  extern unsigned long nsecs_to_jiffies(u64 n);
  
  #define TIMESTAMP_SIZE	30
  
  #endif