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+/**
+ * hdr_histogram.h
+ * Written by Michael Barker and released to the public domain,
+ * as explained at http://creativecommons.org/publicdomain/zero/1.0/
+ *
+ * The source for the hdr_histogram utilises a few C99 constructs, specifically
+ * the use of stdint/stdbool and inline variable declaration.
+ */
+
+#ifndef HDR_HISTOGRAM_H
+#define HDR_HISTOGRAM_H 1
+
+#include <stdint.h>
+#include <stdbool.h>
+#include <stdio.h>
+
+struct hdr_histogram
+{
+ int64_t lowest_discernible_value;
+ int64_t highest_trackable_value;
+ int32_t unit_magnitude;
+ int32_t significant_figures;
+ int32_t sub_bucket_half_count_magnitude;
+ int32_t sub_bucket_half_count;
+ int64_t sub_bucket_mask;
+ int32_t sub_bucket_count;
+ int32_t bucket_count;
+ int64_t min_value;
+ int64_t max_value;
+ int32_t normalizing_index_offset;
+ double conversion_ratio;
+ int32_t counts_len;
+ int64_t total_count;
+ int64_t* counts;
+};
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * Allocate the memory and initialise the hdr_histogram.
+ *
+ * Due to the size of the histogram being the result of some reasonably
+ * involved math on the input parameters this function it is tricky to stack allocate.
+ * The histogram should be released with hdr_close
+ *
+ * @param lowest_discernible_value The smallest possible value that is distinguishable from 0.
+ * Must be a positive integer that is >= 1. May be internally rounded down to nearest power of 2.
+ * @param highest_trackable_value The largest possible value to be put into the
+ * histogram.
+ * @param significant_figures The level of precision for this histogram, i.e. the number
+ * of figures in a decimal number that will be maintained. E.g. a value of 3 will mean
+ * the results from the histogram will be accurate up to the first three digits. Must
+ * be a value between 1 and 5 (inclusive).
+ * @param result Output parameter to capture allocated histogram.
+ * @return 0 on success, EINVAL if lowest_discernible_value is < 1 or the
+ * significant_figure value is outside of the allowed range, ENOMEM if malloc
+ * failed.
+ */
+int hdr_init(
+ int64_t lowest_discernible_value,
+ int64_t highest_trackable_value,
+ int significant_figures,
+ struct hdr_histogram** result);
+
+/**
+ * Free the memory and close the hdr_histogram.
+ *
+ * @param h The histogram you want to close.
+ */
+void hdr_close(struct hdr_histogram* h);
+
+/**
+ * Allocate the memory and initialise the hdr_histogram. This is the equivalent of calling
+ * hdr_init(1, highest_trackable_value, significant_figures, result);
+ *
+ * @deprecated use hdr_init.
+ */
+int hdr_alloc(int64_t highest_trackable_value, int significant_figures, struct hdr_histogram** result);
+
+
+/**
+ * Reset a histogram to zero - empty out a histogram and re-initialise it
+ *
+ * If you want to re-use an existing histogram, but reset everything back to zero, this
+ * is the routine to use.
+ *
+ * @param h The histogram you want to reset to empty.
+ *
+ */
+void hdr_reset(struct hdr_histogram* h);
+
+/**
+ * Get the memory size of the hdr_histogram.
+ *
+ * @param h "This" pointer
+ * @return The amount of memory used by the hdr_histogram in bytes
+ */
+size_t hdr_get_memory_size(struct hdr_histogram* h);
+
+/**
+ * Records a value in the histogram, will round this value of to a precision at or better
+ * than the significant_figure specified at construction time.
+ *
+ * @param h "This" pointer
+ * @param value Value to add to the histogram
+ * @return false if the value is larger than the highest_trackable_value and can't be recorded,
+ * true otherwise.
+ */
+bool hdr_record_value(struct hdr_histogram* h, int64_t value);
+
+/**
+ * Records a value in the histogram, will round this value of to a precision at or better
+ * than the significant_figure specified at construction time.
+ *
+ * Will record this value atomically, however the whole structure may appear inconsistent
+ * when read concurrently with this update. Do NOT mix calls to this method with calls
+ * to non-atomic updates.
+ *
+ * @param h "This" pointer
+ * @param value Value to add to the histogram
+ * @return false if the value is larger than the highest_trackable_value and can't be recorded,
+ * true otherwise.
+ */
+bool hdr_record_value_atomic(struct hdr_histogram* h, int64_t value);
+
+/**
+ * Records count values in the histogram, will round this value of to a
+ * precision at or better than the significant_figure specified at construction
+ * time.
+ *
+ * @param h "This" pointer
+ * @param value Value to add to the histogram
+ * @param count Number of 'value's to add to the histogram
+ * @return false if any value is larger than the highest_trackable_value and can't be recorded,
+ * true otherwise.
+ */
+bool hdr_record_values(struct hdr_histogram* h, int64_t value, int64_t count);
+
+/**
+ * Records count values in the histogram, will round this value of to a
+ * precision at or better than the significant_figure specified at construction
+ * time.
+ *
+ * Will record this value atomically, however the whole structure may appear inconsistent
+ * when read concurrently with this update. Do NOT mix calls to this method with calls
+ * to non-atomic updates.
+ *
+ * @param h "This" pointer
+ * @param value Value to add to the histogram
+ * @param count Number of 'value's to add to the histogram
+ * @return false if any value is larger than the highest_trackable_value and can't be recorded,
+ * true otherwise.
+ */
+bool hdr_record_values_atomic(struct hdr_histogram* h, int64_t value, int64_t count);
+
+/**
+ * Record a value in the histogram and backfill based on an expected interval.
+ *
+ * Records a value in the histogram, will round this value of to a precision at or better
+ * than the significant_figure specified at construction time. This is specifically used
+ * for recording latency. If the value is larger than the expected_interval then the
+ * latency recording system has experienced co-ordinated omission. This method fills in the
+ * values that would have occurred had the client providing the load not been blocked.
+
+ * @param h "This" pointer
+ * @param value Value to add to the histogram
+ * @param expected_interval The delay between recording values.
+ * @return false if the value is larger than the highest_trackable_value and can't be recorded,
+ * true otherwise.
+ */
+bool hdr_record_corrected_value(struct hdr_histogram* h, int64_t value, int64_t expected_interval);
+
+/**
+ * Record a value in the histogram and backfill based on an expected interval.
+ *
+ * Records a value in the histogram, will round this value of to a precision at or better
+ * than the significant_figure specified at construction time. This is specifically used
+ * for recording latency. If the value is larger than the expected_interval then the
+ * latency recording system has experienced co-ordinated omission. This method fills in the
+ * values that would have occurred had the client providing the load not been blocked.
+ *
+ * Will record this value atomically, however the whole structure may appear inconsistent
+ * when read concurrently with this update. Do NOT mix calls to this method with calls
+ * to non-atomic updates.
+ *
+ * @param h "This" pointer
+ * @param value Value to add to the histogram
+ * @param expected_interval The delay between recording values.
+ * @return false if the value is larger than the highest_trackable_value and can't be recorded,
+ * true otherwise.
+ */
+bool hdr_record_corrected_value_atomic(struct hdr_histogram* h, int64_t value, int64_t expected_interval);
+
+/**
+ * Record a value in the histogram 'count' times. Applies the same correcting logic
+ * as 'hdr_record_corrected_value'.
+ *
+ * @param h "This" pointer
+ * @param value Value to add to the histogram
+ * @param count Number of 'value's to add to the histogram
+ * @param expected_interval The delay between recording values.
+ * @return false if the value is larger than the highest_trackable_value and can't be recorded,
+ * true otherwise.
+ */
+bool hdr_record_corrected_values(struct hdr_histogram* h, int64_t value, int64_t count, int64_t expected_interval);
+
+/**
+ * Record a value in the histogram 'count' times. Applies the same correcting logic
+ * as 'hdr_record_corrected_value'.
+ *
+ * Will record this value atomically, however the whole structure may appear inconsistent
+ * when read concurrently with this update. Do NOT mix calls to this method with calls
+ * to non-atomic updates.
+ *
+ * @param h "This" pointer
+ * @param value Value to add to the histogram
+ * @param count Number of 'value's to add to the histogram
+ * @param expected_interval The delay between recording values.
+ * @return false if the value is larger than the highest_trackable_value and can't be recorded,
+ * true otherwise.
+ */
+bool hdr_record_corrected_values_atomic(struct hdr_histogram* h, int64_t value, int64_t count, int64_t expected_interval);
+
+/**
+ * Adds all of the values from 'from' to 'this' histogram. Will return the
+ * number of values that are dropped when copying. Values will be dropped
+ * if they around outside of h.lowest_discernible_value and
+ * h.highest_trackable_value.
+ *
+ * @param h "This" pointer
+ * @param from Histogram to copy values from.
+ * @return The number of values dropped when copying.
+ */
+int64_t hdr_add(struct hdr_histogram* h, const struct hdr_histogram* from);
+
+/**
+ * Adds all of the values from 'from' to 'this' histogram. Will return the
+ * number of values that are dropped when copying. Values will be dropped
+ * if they around outside of h.lowest_discernible_value and
+ * h.highest_trackable_value.
+ *
+ * @param h "This" pointer
+ * @param from Histogram to copy values from.
+ * @return The number of values dropped when copying.
+ */
+int64_t hdr_add_while_correcting_for_coordinated_omission(
+ struct hdr_histogram* h, struct hdr_histogram* from, int64_t expected_interval);
+
+/**
+ * Get minimum value from the histogram. Will return 2^63-1 if the histogram
+ * is empty.
+ *
+ * @param h "This" pointer
+ */
+int64_t hdr_min(const struct hdr_histogram* h);
+
+/**
+ * Get maximum value from the histogram. Will return 0 if the histogram
+ * is empty.
+ *
+ * @param h "This" pointer
+ */
+int64_t hdr_max(const struct hdr_histogram* h);
+
+/**
+ * Get the value at a specific percentile.
+ *
+ * @param h "This" pointer.
+ * @param percentile The percentile to get the value for
+ */
+int64_t hdr_value_at_percentile(const struct hdr_histogram* h, double percentile);
+
+/**
+ * Get the values at the given percentiles.
+ *
+ * @param h "This" pointer.
+ * @param percentiles The ordered percentiles array to get the values for.
+ * @param length Number of elements in the arrays.
+ * @param values Destination array containing the values at the given percentiles.
+ * The values array should be allocated by the caller.
+ * @return 0 on success, ENOMEM if the provided destination array is null.
+ */
+int hdr_value_at_percentiles(const struct hdr_histogram *h, const double *percentiles, int64_t *values, size_t length);
+
+/**
+ * Gets the standard deviation for the values in the histogram.
+ *
+ * @param h "This" pointer
+ * @return The standard deviation
+ */
+double hdr_stddev(const struct hdr_histogram* h);
+
+/**
+ * Gets the mean for the values in the histogram.
+ *
+ * @param h "This" pointer
+ * @return The mean
+ */
+double hdr_mean(const struct hdr_histogram* h);
+
+/**
+ * Determine if two values are equivalent with the histogram's resolution.
+ * Where "equivalent" means that value samples recorded for any two
+ * equivalent values are counted in a common total count.
+ *
+ * @param h "This" pointer
+ * @param a first value to compare
+ * @param b second value to compare
+ * @return 'true' if values are equivalent with the histogram's resolution.
+ */
+bool hdr_values_are_equivalent(const struct hdr_histogram* h, int64_t a, int64_t b);
+
+/**
+ * Get the lowest value that is equivalent to the given value within the histogram's resolution.
+ * Where "equivalent" means that value samples recorded for any two
+ * equivalent values are counted in a common total count.
+ *
+ * @param h "This" pointer
+ * @param value The given value
+ * @return The lowest value that is equivalent to the given value within the histogram's resolution.
+ */
+int64_t hdr_lowest_equivalent_value(const struct hdr_histogram* h, int64_t value);
+
+/**
+ * Get the count of recorded values at a specific value
+ * (to within the histogram resolution at the value level).
+ *
+ * @param h "This" pointer
+ * @param value The value for which to provide the recorded count
+ * @return The total count of values recorded in the histogram within the value range that is
+ * {@literal >=} lowestEquivalentValue(<i>value</i>) and {@literal <=} highestEquivalentValue(<i>value</i>)
+ */
+int64_t hdr_count_at_value(const struct hdr_histogram* h, int64_t value);
+
+int64_t hdr_count_at_index(const struct hdr_histogram* h, int32_t index);
+
+int64_t hdr_value_at_index(const struct hdr_histogram* h, int32_t index);
+
+struct hdr_iter_percentiles
+{
+ bool seen_last_value;
+ int32_t ticks_per_half_distance;
+ double percentile_to_iterate_to;
+ double percentile;
+};
+
+struct hdr_iter_recorded
+{
+ int64_t count_added_in_this_iteration_step;
+};
+
+struct hdr_iter_linear
+{
+ int64_t value_units_per_bucket;
+ int64_t count_added_in_this_iteration_step;
+ int64_t next_value_reporting_level;
+ int64_t next_value_reporting_level_lowest_equivalent;
+};
+
+struct hdr_iter_log
+{
+ double log_base;
+ int64_t count_added_in_this_iteration_step;
+ int64_t next_value_reporting_level;
+ int64_t next_value_reporting_level_lowest_equivalent;
+};
+
+/**
+ * The basic iterator. This is a generic structure
+ * that supports all of the types of iteration. Use
+ * the appropriate initialiser to get the desired
+ * iteration.
+ *
+ * @
+ */
+struct hdr_iter
+{
+ const struct hdr_histogram* h;
+ /** raw index into the counts array */
+ int32_t counts_index;
+ /** snapshot of the length at the time the iterator is created */
+ int64_t total_count;
+ /** value directly from array for the current counts_index */
+ int64_t count;
+ /** sum of all of the counts up to and including the count at this index */
+ int64_t cumulative_count;
+ /** The current value based on counts_index */
+ int64_t value;
+ int64_t highest_equivalent_value;
+ int64_t lowest_equivalent_value;
+ int64_t median_equivalent_value;
+ int64_t value_iterated_from;
+ int64_t value_iterated_to;
+
+ union
+ {
+ struct hdr_iter_percentiles percentiles;
+ struct hdr_iter_recorded recorded;
+ struct hdr_iter_linear linear;
+ struct hdr_iter_log log;
+ } specifics;
+
+ bool (* _next_fp)(struct hdr_iter* iter);
+
+};
+
+/**
+ * Initalises the basic iterator.
+ *
+ * @param itr 'This' pointer
+ * @param h The histogram to iterate over
+ */
+void hdr_iter_init(struct hdr_iter* iter, const struct hdr_histogram* h);
+
+/**
+ * Initialise the iterator for use with percentiles.
+ */
+void hdr_iter_percentile_init(struct hdr_iter* iter, const struct hdr_histogram* h, int32_t ticks_per_half_distance);
+
+/**
+ * Initialise the iterator for use with recorded values.
+ */
+void hdr_iter_recorded_init(struct hdr_iter* iter, const struct hdr_histogram* h);
+
+/**
+ * Initialise the iterator for use with linear values.
+ */
+void hdr_iter_linear_init(
+ struct hdr_iter* iter,
+ const struct hdr_histogram* h,
+ int64_t value_units_per_bucket);
+
+/**
+ * Update the iterator value units per bucket
+ */
+void hdr_iter_linear_set_value_units_per_bucket(struct hdr_iter* iter, int64_t value_units_per_bucket);
+
+/**
+ * Initialise the iterator for use with logarithmic values
+ */
+void hdr_iter_log_init(
+ struct hdr_iter* iter,
+ const struct hdr_histogram* h,
+ int64_t value_units_first_bucket,
+ double log_base);
+
+/**
+ * Iterate to the next value for the iterator. If there are no more values
+ * available return faluse.
+ *
+ * @param itr 'This' pointer
+ * @return 'false' if there are no values remaining for this iterator.
+ */
+bool hdr_iter_next(struct hdr_iter* iter);
+
+typedef enum
+{
+ CLASSIC,
+ CSV
+} format_type;
+
+/**
+ * Print out a percentile based histogram to the supplied stream. Note that
+ * this call will not flush the FILE, this is left up to the user.
+ *
+ * @param h 'This' pointer
+ * @param stream The FILE to write the output to
+ * @param ticks_per_half_distance The number of iteration steps per half-distance to 100%
+ * @param value_scale Scale the output values by this amount
+ * @param format_type Format to use, e.g. CSV.
+ * @return 0 on success, error code on failure. EIO if an error occurs writing
+ * the output.
+ */
+int hdr_percentiles_print(
+ struct hdr_histogram* h, FILE* stream, int32_t ticks_per_half_distance,
+ double value_scale, format_type format);
+
+/**
+* Internal allocation methods, used by hdr_dbl_histogram.
+*/
+struct hdr_histogram_bucket_config
+{
+ int64_t lowest_discernible_value;
+ int64_t highest_trackable_value;
+ int64_t unit_magnitude;
+ int64_t significant_figures;
+ int32_t sub_bucket_half_count_magnitude;
+ int32_t sub_bucket_half_count;
+ int64_t sub_bucket_mask;
+ int32_t sub_bucket_count;
+ int32_t bucket_count;
+ int32_t counts_len;
+};
+
+int hdr_calculate_bucket_config(
+ int64_t lowest_discernible_value,
+ int64_t highest_trackable_value,
+ int significant_figures,
+ struct hdr_histogram_bucket_config* cfg);
+
+void hdr_init_preallocated(struct hdr_histogram* h, struct hdr_histogram_bucket_config* cfg);
+
+int64_t hdr_size_of_equivalent_value_range(const struct hdr_histogram* h, int64_t value);
+
+int64_t hdr_next_non_equivalent_value(const struct hdr_histogram* h, int64_t value);
+
+int64_t hdr_median_equivalent_value(const struct hdr_histogram* h, int64_t value);
+
+/**
+ * Used to reset counters after importing data manually into the histogram, used by the logging code
+ * and other custom serialisation tools.
+ */
+void hdr_reset_internal_counters(struct hdr_histogram* h);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif