text: // Copyright 2018 The Fuchsia Authors
  //
  // Use of this source code is governed by a MIT-style
  // license that can be found in the LICENSE file or at
  // https://opensource.org/licenses/MIT
  
  #ifndef SYSROOT_ZIRCON_TIME_H_
  #define SYSROOT_ZIRCON_TIME_H_
  
  #include <stdint.h>
  #include <zircon/compiler.h>
  
  __BEGIN_CDECLS
  
  // absolute time in nanoseconds (generally with respect to the monotonic clock)
  typedef int64_t zx_time_t;
  // a duration in nanoseconds
  typedef int64_t zx_duration_t;
  // a duration in hardware ticks
  typedef uint64_t zx_ticks_t;
  
  #define ZX_TIME_INFINITE INT64_MAX
  #define ZX_TIME_INFINITE_PAST INT64_MIN
  
  // These functions perform overflow-safe time arithmetic and unit conversion, clamping to
  // ZX_TIME_INFINITE in case of overflow and ZX_TIME_INFINITE_PAST in case of underflow.
  //
  // C++ code should use zx::time and zx::duration instead.
  //
  // For arithmetic the naming scheme is:
  //     zx_<first argument>_<operation>_<second argument>
  //
  // For unit conversion the naming scheme is:
  //     zx_duration_from_<unit of argument>
  //
  // TODO(maniscalco): Consider expanding the set of operations to include division, modulo, and
  // floating point math.
  
  __CONSTEXPR static inline zx_time_t zx_time_add_duration(zx_time_t time, zx_duration_t duration) {
      zx_time_t x = 0;
      if (unlikely(add_overflow(time, duration, &x))) {
          if (x >= 0) {
              return ZX_TIME_INFINITE_PAST;
          } else {
              return ZX_TIME_INFINITE;
          }
      }
      return x;
  }
  
  __CONSTEXPR static inline zx_time_t zx_time_sub_duration(zx_time_t time, zx_duration_t duration) {
      zx_time_t x = 0;
      if (unlikely(sub_overflow(time, duration, &x))) {
          if (x >= 0) {
              return ZX_TIME_INFINITE_PAST;
          } else {
              return ZX_TIME_INFINITE;
          }
      }
      return x;
  }
  
  __CONSTEXPR static inline zx_duration_t zx_time_sub_time(zx_time_t time1, zx_time_t time2) {
      zx_duration_t x = 0;
      if (unlikely(sub_overflow(time1, time2, &x))) {
          if (x >= 0) {
              return ZX_TIME_INFINITE_PAST;
          } else {
              return ZX_TIME_INFINITE;
          }
      }
      return x;
  }
  
  __CONSTEXPR static inline zx_duration_t zx_duration_add_duration(zx_duration_t dur1,
                                                                   zx_duration_t dur2) {
      zx_duration_t x = 0;
      if (unlikely(add_overflow(dur1, dur2, &x))) {
          if (x >= 0) {
              return ZX_TIME_INFINITE_PAST;
          } else {
              return ZX_TIME_INFINITE;
          }
      }
      return x;
  }
  
  __CONSTEXPR static inline zx_duration_t zx_duration_sub_duration(zx_duration_t dur1,
                                                                   zx_duration_t dur2) {
      zx_duration_t x = 0;
      if (unlikely(sub_overflow(dur1, dur2, &x))) {
          if (x >= 0) {
              return ZX_TIME_INFINITE_PAST;
          } else {
              return ZX_TIME_INFINITE;
          }
      }
      return x;
  }
  
  __CONSTEXPR static inline zx_duration_t zx_duration_mul_int64(zx_duration_t duration,
                                                                int64_t multiplier) {
      zx_duration_t x = 0;
      if (unlikely(mul_overflow(duration, multiplier, &x))) {
          if ((duration > 0 && multiplier > 0) || (duration < 0 && multiplier < 0)) {
              return ZX_TIME_INFINITE;
          } else {
              return ZX_TIME_INFINITE_PAST;
          }
      }
      return x;
  }
  
  __CONSTEXPR static inline int64_t zx_nsec_from_duration(zx_duration_t n) {
      return n;
  }
  
  __CONSTEXPR static inline zx_duration_t zx_duration_from_nsec(int64_t n) {
      return zx_duration_mul_int64(1, n);
  }
  
  __CONSTEXPR static inline zx_duration_t zx_duration_from_usec(int64_t n) {
      return zx_duration_mul_int64(1000, n);
  }
  
  __CONSTEXPR static inline zx_duration_t zx_duration_from_msec(int64_t n) {
      return zx_duration_mul_int64(1000000, n);
  }
  
  __CONSTEXPR static inline zx_duration_t zx_duration_from_sec(int64_t n) {
      return zx_duration_mul_int64(1000000000, n);
  }
  
  __CONSTEXPR static inline zx_duration_t zx_duration_from_min(int64_t n) {
      return zx_duration_mul_int64(60000000000, n);
  }
  
  __CONSTEXPR static inline zx_duration_t zx_duration_from_hour(int64_t n) {
      return zx_duration_mul_int64(3600000000000, n);
  }
  
  // Similar to the functions above, these macros perform overflow-safe unit conversion. Prefer to use
  // the functions above instead of these macros.
  #define ZX_NSEC(n) \
      (__ISCONSTANT(n) ? ((zx_duration_t)(1LL * (n))) : (zx_duration_from_nsec(n)))
  #define ZX_USEC(n) \
      (__ISCONSTANT(n) ? ((zx_duration_t)(1000LL * (n))) : (zx_duration_from_usec(n)))
  #define ZX_MSEC(n) \
      (__ISCONSTANT(n) ? ((zx_duration_t)(1000000LL * (n))) : (zx_duration_from_msec(n)))
  #define ZX_SEC(n) \
      (__ISCONSTANT(n) ? ((zx_duration_t)(1000000000LL * (n))) : (zx_duration_from_sec(n)))
  #define ZX_MIN(n) \
      (__ISCONSTANT(n) ? ((zx_duration_t)(60LL * 1000000000LL * (n))) : (zx_duration_from_min(n)))
  #define ZX_HOUR(n) \
      (__ISCONSTANT(n) ? ((zx_duration_t)(3600LL * 1000000000LL * (n))) : (zx_duration_from_hour(n)))
  
  __END_CDECLS
  
  #endif  // SYSROOT_ZIRCON_TIME_H_
  