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Add histogram fields in header file that allow specifying edges.
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@ -228,13 +228,15 @@ typedef uint16_t circpad_statenum_t;
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#define CIRCPAD_STATENUM_MAX (UINT16_MAX)
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/** A histogram is used to sample padding delays given a machine state. This
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* constant defines the maximum histogram width (i.e. the max number of bins)
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* constant defines the maximum histogram width (i.e. the max number of bins).
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*
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* Each histogram bin is twice as large as the previous. Two exceptions: The
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* first bin has zero width (which means that minimum delay is applied to the
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* next padding cell), and the last bin (infinity bin) has infinite width
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* (which means that the next padding cell will be delayed infinitely). */
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#define CIRCPAD_MAX_HISTOGRAM_LEN (sizeof(circpad_delay_t)*8 + 1)
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* The current limit is arbitrary and could be raised if there is a need,
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* however too many bins will be hard to serialize in the future.
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*
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* Memory concerns are not so great here since the corresponding histogram and
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* histogram_edges arrays are global and not per-circuit.
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*/
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#define CIRCPAD_MAX_HISTOGRAM_LEN (100)
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/**
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* A state of a padding state machine. The information here are immutable and
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@ -248,15 +250,48 @@ typedef uint16_t circpad_statenum_t;
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* or the consensus.
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*/
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typedef struct circpad_state_t {
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/** If a histogram is used for this state, this specifies the number of bins
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* of this histogram. Histograms must have at least 2 bins.
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/**
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* If a histogram is used for this state, this specifies the number of bins
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* of this histogram. Histograms must have at least 2 bins.
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*
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* If a delay probability distribution is used for this state, this is set
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* to 0. */
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* In particular, the following histogram:
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*
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* Tokens
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* +
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* 10 | +----+
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* 9 | | | +---------+
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* 8 | | | | |
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* 7 | | | +-----+ |
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* 6 +----+ Bin+-----+ | +---------------+
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* 5 | | #1 | | | | |
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* | Bin| | Bin | Bin | Bin #4 | Bin #5 |
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* | #0 | | #2 | #3 | | (infinity bin)|
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* | | | | | | |
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* | | | | | | |
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* 0 +----+----+-----+-----+---------+---------------+
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* 0 100 200 350 500 1000 ∞ microseconds
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*
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* would be specified the following way:
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* histogram_len = 6;
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* histogram[] = { 6, 10, 6, 7, 9, 6 }
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* histogram_edges[] = { 0, 100, 200, 350, 500, 1000 }
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*
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* If a delay probability distribution is used for this state, this is set
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* to 0. */
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circpad_hist_index_t histogram_len;
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/** The histogram itself: an array of uint16s of tokens, whose
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* widths are exponentially spaced, in microseconds */
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* widths are exponentially spaced, in microseconds.
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*
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* This array must have histogram_len elements. */
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circpad_hist_token_t histogram[CIRCPAD_MAX_HISTOGRAM_LEN];
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/* The histogram bin edges in usec.
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*
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* Each element of this array specifies the left edge of the corresponding
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* bin. The rightmost edge is always infinity and is not specified in this
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* array.
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*
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* This array must have histogram_len+1 elements. */
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circpad_delay_t histogram_edges[CIRCPAD_MAX_HISTOGRAM_LEN+1];
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/** Total number of tokens in this histogram. This is a constant and is *not*
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* decremented every time we spend a token. It's used for initializing and
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* refilling the histogram. */
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