-/*
- * 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 used 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 take 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 USEC_JIFFIE_SC (SEC_JIFFIE_SC + 19)
-#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))
-#define USEC_CONVERSION \
- ((unsigned long)((((u64)NSEC_PER_USEC << USEC_JIFFIE_SC) +\
- TICK_NSEC -1) / (u64)TICK_NSEC))
-/*
- * USEC_ROUND is used in the timeval to jiffie conversion. See there
- * for more details. It is the scaled resolution rounding value. Note
- * that it is a 64-bit value. Since, when it is applied, we are already
- * in jiffies (albit scaled), it is nothing but the bits we will shift
- * off.
- */
-#define USEC_ROUND (u64)(((u64)1 << USEC_JIFFIE_SC) - 1)
-/*
- * 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 jiffies to milliseconds and back.
- *
- * Avoid unnecessary multiplications/divisions in the
- * two most common HZ cases:
- */
-static inline unsigned int jiffies_to_msecs(const unsigned long j)
-{
-#if HZ <= 1000 && !(1000 % HZ)
- return (1000 / HZ) * j;
-#elif HZ > 1000 && !(HZ % 1000)
- return (j + (HZ / 1000) - 1)/(HZ / 1000);
-#else
- return (j * 1000) / HZ;
-#endif
-}
-
-static inline unsigned int jiffies_to_usecs(const unsigned long j)
-{
-#if HZ <= 1000 && !(1000 % HZ)
- return (1000000 / HZ) * j;
-#elif HZ > 1000 && !(HZ % 1000)
- return (j*1000 + (HZ - 1000))/(HZ / 1000);
-#else
- return (j * 1000000) / HZ;
-#endif
-}
-
-static inline unsigned long msecs_to_jiffies(const unsigned int m)
-{
- if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
- return MAX_JIFFY_OFFSET;
-#if HZ <= 1000 && !(1000 % HZ)
- return (m + (1000 / HZ) - 1) / (1000 / HZ);
-#elif HZ > 1000 && !(HZ % 1000)
- return m * (HZ / 1000);
-#else
- return (m * HZ + 999) / 1000;
-#endif
-}
-
-/*
- * The TICK_NSEC - 1 rounds up the value to the next resolution. Note
- * that a remainder subtract here would not do the right thing as the
- * resolution values don't fall on second boundries. I.e. the line:
- * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding.
- *
- * Rather, we just shift the bits off the right.
- *
- * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec
- * value to a scaled second value.
- */
-static __inline__ unsigned long
-timespec_to_jiffies(const struct timespec *value)
-{
- unsigned long sec = value->tv_sec;
- long nsec = value->tv_nsec + TICK_NSEC - 1;
-
- if (sec >= MAX_SEC_IN_JIFFIES){
- sec = MAX_SEC_IN_JIFFIES;
- nsec = 0;
- }
- return (((u64)sec * SEC_CONVERSION) +
- (((u64)nsec * NSEC_CONVERSION) >>
- (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
-
-}
-
-static __inline__ void
-jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
-{
- /*
- * Convert jiffies to nanoseconds and separate with
- * one divide.
- */
- u64 nsec = (u64)jiffies * TICK_NSEC;
- value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &value->tv_nsec);
-}
-
-/* Same for "timeval"
- *
- * Well, almost. The problem here is that the real system resolution is
- * in nanoseconds and the value being converted is in micro seconds.
- * Also for some machines (those that use HZ = 1024, in-particular),
- * there is a LARGE error in the tick size in microseconds.
-
- * The solution we use is to do the rounding AFTER we convert the
- * microsecond part. Thus the USEC_ROUND, the bits to be shifted off.
- * Instruction wise, this should cost only an additional add with carry
- * instruction above the way it was done above.
- */
-static __inline__ unsigned long
-timeval_to_jiffies(const struct timeval *value)
-{
- unsigned long sec = value->tv_sec;
- long usec = value->tv_usec;
-
- if (sec >= MAX_SEC_IN_JIFFIES){
- sec = MAX_SEC_IN_JIFFIES;
- usec = 0;
- }
- return (((u64)sec * SEC_CONVERSION) +
- (((u64)usec * USEC_CONVERSION + USEC_ROUND) >>
- (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
-}
-
-static __inline__ void
-jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
-{
- /*
- * Convert jiffies to nanoseconds and separate with
- * one divide.
- */
- u64 nsec = (u64)jiffies * TICK_NSEC;
- value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &value->tv_usec);
- value->tv_usec /= NSEC_PER_USEC;
-}
-