1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133

use speedy::{Readable, Writable};
use serde::{Serialize, Deserialize};
use std::ops::Sub;
use chrono;

use super::duration::Duration;

/// Quoting RTPS 2.3 spec 9.3.2.1:
///
/// > The representation of the time is the one defined by the IETF Network Time
/// > Protocol (NTP) Standard (IETF RFC 1305). In this representation, time is
/// > expressed in seconds and fraction of seconds using the formula:
/// > time = seconds + (fraction / 2^(32))
///
/// > The time origin is represented by the reserved value TIME_ZERO and corresponds
/// > to the UNIX prime epoch 0h, 1 January 1970.
///
///
/// *Note* : NTP does not use the Unix epoch (1970-01-01 00:00) but the beginning of
/// the 20th century epoch (1900-01-01 00:00) insted. So these timestamps are not the same
/// as in NTP.

/// This time representation is used in RTPS messages.
/// This is called Time_t in the RTPS spec.
#[derive(
  Debug, PartialEq, Eq, PartialOrd, Ord, Readable, Writable, Clone, Copy, Serialize, Deserialize,
)]
pub struct Timestamp {
  seconds: u32,
  fraction: u32,
}

impl Timestamp {
  // Special contants reserved by the RTPS protocol, from RTPS spec section 9.3.2.
  pub const TIME_ZERO: Timestamp = Timestamp {
    seconds: 0,
    fraction: 0,
  };
  pub const TIME_INVALID: Timestamp = Timestamp {
    seconds: 0xFFFF_FFFF,
    fraction: 0xFFFF_FFFF,
  };
  pub const TIME_INFINITE: Timestamp = Timestamp {
    seconds: 0x7FFF_FFFF,
    fraction: 0xFFFF_FFFF,
  };

  pub fn now() -> Timestamp {
    Timestamp::from_nanos(chrono::Utc::now().timestamp_nanos() as u64)
  }

  fn to_ticks(&self) -> u64 {
    ((self.seconds as u64) << 32) + (self.fraction as u64)
  }

  fn from_ticks(ticks: u64) -> Timestamp {
    Timestamp {
      seconds: (ticks >> 32) as u32,
      fraction: ticks as u32,
    }
  }

  fn from_nanos(nanos_since_unix_epoch: u64) -> Timestamp {
    Timestamp {
      seconds: (nanos_since_unix_epoch / 1_000_000_000) as u32,
      fraction: (((nanos_since_unix_epoch % 1_000_000_000) << 32) / 1_000_000_000) as u32,
    }
  }

  pub fn duration_since(&self, since: Timestamp) -> Duration {
    *self - since
  }
}

impl Sub for Timestamp {
  type Output = Duration;

  fn sub(self, other: Timestamp) -> Duration {
    let a = self.to_ticks();
    let b = other.to_ticks();
    // https://doc.rust-lang.org/1.30.0/book/first-edition/casting-between-types.html
    // "Casting between two integers of the same size (e.g. i32 -> u32) is a no-op"
    Duration::from_ticks(a.wrapping_sub(b) as i64)
  }
}

impl Sub<Duration> for Timestamp {
  type Output = Timestamp;

  fn sub(self, rhs: Duration) -> Self::Output {
    let lhs_ticks = self.to_ticks();
    let rhs_ticks = rhs.to_ticks() as u64;

    Timestamp::from_ticks(lhs_ticks - rhs_ticks)
  }
}

#[cfg(test)]
mod tests {
  use super::*;

  serialization_test!( type = Timestamp,
  {
      time_zero,
      Timestamp::TIME_ZERO,
      le = [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00],
      be = [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00]
  },
  {
      time_invalid,
      Timestamp::TIME_INVALID,
      le = [0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF],
      be = [0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF]
  },
  {
      time_infinite,
      Timestamp::TIME_INFINITE,
      le = [0xFF, 0xFF, 0xFF, 0x7F, 0xFF, 0xFF, 0xFF, 0xFF],
      be = [0x7F, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF]
  },
  {
      time_current_empty_fraction,
      Timestamp { seconds: 1_537_045_491, fraction: 0 },
      le = [0xF3, 0x73, 0x9D, 0x5B, 0x00, 0x00, 0x00, 0x00],
      be = [0x5B, 0x9D, 0x73, 0xF3, 0x00, 0x00, 0x00, 0x00]
  },
  {
      time_from_wireshark,
      Timestamp { seconds: 1_519_152_760, fraction: 1_328_210_046 },
      le = [0x78, 0x6E, 0x8C, 0x5A, 0x7E, 0xE0, 0x2A, 0x4F],
      be = [0x5A, 0x8C, 0x6E, 0x78, 0x4F, 0x2A, 0xE0, 0x7E]
  });
}