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mirror of https://github.com/TomHarte/CLK.git synced 2024-12-27 16:31:31 +00:00

Made an attempt to add the necessary extension to Track, with a concrete implementation in PCMTrack, to support time-based seeking, the intended mechanism for not magically spinning the disk back to the index hole upon every head step.

This commit is contained in:
Thomas Harte 2016-08-03 06:59:45 -04:00
parent d832e5e10d
commit 30f8b6baa4
4 changed files with 64 additions and 2 deletions

View File

@ -37,9 +37,16 @@ class Track {
}; };
/*! /*!
Returns the next event that will be detected during rotation of this disk. @returns the next event that will be detected during rotation of this disk.
*/ */
virtual Event get_next_event() = 0; virtual Event get_next_event() = 0;
/*!
Jumps to the event latest offset that is less than or equal to the input time.
@returns the time jumped to.
*/
virtual Time seek_to(Time time_since_index_hole) = 0;
}; };
/*! /*!

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@ -61,6 +61,45 @@ PCMTrack::Event PCMTrack::get_next_event()
return _next_event; return _next_event;
} }
Time PCMTrack::seek_to(Time time_since_index_hole)
{
_segment_pointer = 0;
// pick a common clock rate for counting time on this track and multiply up the time being sought appropriately
Time time_so_far;
time_so_far.clock_rate = NumberTheory::least_common_multiple(_track_clock_rate, time_since_index_hole.clock_rate);
time_since_index_hole.length *= time_so_far.clock_rate / time_since_index_hole.clock_rate;
time_since_index_hole.clock_rate = time_so_far.clock_rate;
while(_segment_pointer < _segments.size())
{
// determine how long this segment is in terms of the master clock
unsigned int clock_multiplier = time_so_far.clock_rate / _segments[_segment_pointer].length_of_a_bit.clock_rate;
unsigned int resolution_in_this_segment = _segments[_segment_pointer].length_of_a_bit.length * clock_multiplier;
unsigned int time_in_this_segment = resolution_in_this_segment * _segments[_segment_pointer].number_of_bits;
// if this segment goes on longer than the time being sought, end here
unsigned int time_remaining = time_since_index_hole.length - time_so_far.length;
if(time_in_this_segment >= time_remaining)
{
// get the amount of time actually to move into this segment
unsigned int time_found = time_remaining - (time_remaining % resolution_in_this_segment);
// resolve that into the stateful bit count
_bit_pointer = time_remaining / resolution_in_this_segment;
// update and return the time sought to
time_so_far.length += time_found;
return time_so_far;
}
// otherwise, accumulate time and keep moving
time_so_far.length += time_in_this_segment;
_segment_pointer++;
}
return time_since_index_hole;
}
void PCMTrack::fix_length() void PCMTrack::fix_length()
{ {
// find the least common multiple of all segment clock rates // find the least common multiple of all segment clock rates

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@ -47,6 +47,7 @@ class PCMTrack: public Track {
// as per @c Track // as per @c Track
Event get_next_event(); Event get_next_event();
Time seek_to(Time time_since_index_hole);
private: private:
// storage for the segments that describe this track // storage for the segments that describe this track

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@ -19,6 +19,7 @@ namespace Storage {
*/ */
struct Time { struct Time {
unsigned int length, clock_rate; unsigned int length, clock_rate;
Time() : length(0), clock_rate(1) {}
/*! /*!
Reduces this @c Time to its simplest form eliminates all common factors from @c length Reduces this @c Time to its simplest form eliminates all common factors from @c length
@ -32,14 +33,28 @@ struct Time {
} }
/*! /*!
Returns the floating point conversion of this @c Time. This will often be less precise. @returns the floating point conversion of this @c Time. This will often be less precise.
*/ */
inline float get_float() inline float get_float()
{ {
return (float)length / (float)clock_rate; return (float)length / (float)clock_rate;
} }
inline bool operator<(Time &other)
{
return other.clock_rate * length < clock_rate * other.length;
}
inline Time operator+(Time &other)
{
Time result;
result.clock_rate = NumberTheory::least_common_multiple(clock_rate, other.clock_rate);
result.length = length * (clock_rate / result.clock_rate) + other.length * (other.clock_rate / result.clock_rate);
return result;
}
}; };
} }
#endif /* Storage_h */ #endif /* Storage_h */