376 lines
9.9 KiB
C
376 lines
9.9 KiB
C
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/* Lots of code for an adaptive, stable, natural mergesort. There are many
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* pieces to this algorithm; read listsort.txt for overviews and details.
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*/
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#include "config.h"
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#include "gtktimsortprivate.h"
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/*
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* This is the minimum sized sequence that will be merged. Shorter
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* sequences will be lengthened by calling binarySort. If the entire
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* array is less than this length, no merges will be performed.
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*
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* This constant should be a power of two. It was 64 in Tim Peter's C
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* implementation, but 32 was empirically determined to work better in
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* [Android's Java] implementation. In the unlikely event that you set
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* this constant to be a number that's not a power of two, you'll need
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* to change the compute_min_run() computation.
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*
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* If you decrease this constant, you must change the
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* GTK_TIM_SORT_MAX_PENDING value, or you risk running out of space.
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* See Python's listsort.txt for a discussion of the minimum stack
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* length required as a function of the length of the array being sorted and
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* the minimum merge sequence length.
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*/
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#define MIN_MERGE 32
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/*
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* When we get into galloping mode, we stay there until both runs win less
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* often than MIN_GALLOP consecutive times.
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*/
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#define MIN_GALLOP 7
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/*
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* Returns the minimum acceptable run length for an array of the specified
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* length. Natural runs shorter than this will be extended with binary sort.
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*
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* Roughly speaking, the computation is:
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*
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* If n < MIN_MERGE, return n (it's too small to bother with fancy stuff).
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* Else if n is an exact power of 2, return MIN_MERGE/2.
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* Else return an int k, MIN_MERGE/2 <= k <= MIN_MERGE, such that n/k
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* is close to, but strictly less than, an exact power of 2.
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*
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* For the rationale, see listsort.txt.
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*
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* @param n the length of the array to be sorted
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* @return the length of the minimum run to be merged
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*/
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static gsize
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compute_min_run (gsize n)
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{
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gsize r = 0; // Becomes 1 if any 1 bits are shifted off
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while (n >= MIN_MERGE) {
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r |= (n & 1);
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n >>= 1;
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}
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return n + r;
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}
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void
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gtk_tim_sort_init (GtkTimSort *self,
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gpointer base,
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gsize size,
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gsize element_size,
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GCompareDataFunc compare_func,
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gpointer data)
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{
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self->element_size = element_size;
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self->base = base;
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self->size = size;
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self->compare_func = compare_func;
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self->data = data;
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self->min_gallop = MIN_GALLOP;
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self->max_merge_size = G_MAXSIZE;
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self->min_run = compute_min_run (size);
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self->tmp = NULL;
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self->tmp_length = 0;
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self->pending_runs = 0;
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}
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void
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gtk_tim_sort_finish (GtkTimSort *self)
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{
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g_clear_pointer (&self->tmp, g_free);
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}
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void
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gtk_tim_sort (gpointer base,
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gsize size,
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gsize element_size,
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GCompareDataFunc compare_func,
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gpointer user_data)
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{
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GtkTimSort self;
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gtk_tim_sort_init (&self, base, size, element_size, compare_func, user_data);
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while (gtk_tim_sort_step (&self, NULL));
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gtk_tim_sort_finish (&self);
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}
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static inline int
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gtk_tim_sort_compare (GtkTimSort *self,
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gpointer a,
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gpointer b)
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{
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return self->compare_func (a, b, self->data);
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}
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/**
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* Pushes the specified run onto the pending-run stack.
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*
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* @param runBase index of the first element in the run
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* @param runLen the number of elements in the run
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*/
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static void
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gtk_tim_sort_push_run (GtkTimSort *self,
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void *base,
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gsize len)
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{
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g_assert (self->pending_runs < GTK_TIM_SORT_MAX_PENDING);
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g_assert (len <= self->size);
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self->run[self->pending_runs].base = base;
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self->run[self->pending_runs].len = len;
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self->pending_runs++;
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/* Advance to find next run */
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self->base = ((char *) self->base) + len * self->element_size;
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self->size -= len;
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}
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/**
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* Ensures that the external array tmp has at least the specified
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* number of elements, increasing its size if necessary. The size
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* increases exponentially to ensure amortized linear time complexity.
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*
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* @param min_capacity the minimum required capacity of the tmp array
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* @return tmp, whether or not it grew
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*/
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static gpointer
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gtk_tim_sort_ensure_capacity (GtkTimSort *self,
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gsize min_capacity)
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{
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if (self->tmp_length < min_capacity)
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{
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/* Compute smallest power of 2 > min_capacity */
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gsize new_size = min_capacity;
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new_size |= new_size >> 1;
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new_size |= new_size >> 2;
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new_size |= new_size >> 4;
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new_size |= new_size >> 8;
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new_size |= new_size >> 16;
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if (sizeof(new_size) > 4)
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new_size |= new_size >> 32;
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new_size++;
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if (new_size == 0) /* (overflow) Not bloody likely! */
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new_size = min_capacity;
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g_free (self->tmp);
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self->tmp_length = new_size;
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self->tmp = g_malloc (self->tmp_length * self->element_size);
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}
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return self->tmp;
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}
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static void
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gtk_tim_sort_set_change (GtkTimSortRun *out_change,
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gpointer base,
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gsize len)
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{
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if (out_change)
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{
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out_change->base = base;
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out_change->len = len;
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}
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}
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/*<private>
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* gtk_tim_sort_get_runs:
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* @self: a GtkTimSort
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* @runs: (out) (caller-allocates): Place to store the 0-terminated list of
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* runs
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*
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* Stores the already presorted list of runs - ranges of items that are
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* known to be sorted among themselves.
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*
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* This can be used with gtk_tim_sort_set_runs() when resuming a sort later.
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**/
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void
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gtk_tim_sort_get_runs (GtkTimSort *self,
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gsize runs[GTK_TIM_SORT_MAX_PENDING + 1])
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{
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gsize i;
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g_return_if_fail (self);
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g_return_if_fail (runs);
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for (i = 0; i < self->pending_runs; i++)
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runs[i] = self->run[i].len;
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runs[self->pending_runs] = 0;
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}
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/*<private>
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* gtk_tim_sort_set_runs:
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* @self: a freshly initialized GtkTimSort
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* @runs: (array length=zero-terminated): a 0-terminated list of runs
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*
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* Sets the list of runs. A run is a range of items that are already
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* sorted correctly among themselves. Runs must appear at the beginning of
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* the array.
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*
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* Runs can only be set at the beginning of the sort operation.
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**/
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void
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gtk_tim_sort_set_runs (GtkTimSort *self,
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gsize *runs)
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{
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gsize i;
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g_return_if_fail (self);
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g_return_if_fail (self->pending_runs == 0);
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for (i = 0; runs[i] != 0; i++)
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gtk_tim_sort_push_run (self, self->base, runs[i]);
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}
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/*
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* gtk_tim_sort_set_max_merge_size:
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* @self: a GtkTimSort
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* @max_merge_size: Maximum size of a merge step, 0 for unlimited
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*
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* Sets the maximum size of a merge step. Every time
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* gtk_tim_sort_step() is called and a merge operation has to be
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* done, the @max_merge_size will be used to limit the size of
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* the merge.
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*
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* The benefit is that merges happen faster, and if you're using
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* an incremental sorting algorithm in the main thread, this will
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* limit the runtime.
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*
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* The disadvantage is that setting up merges is expensive and that
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* various optimizations benefit from larger merges, so the total
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* runtime of the sorting will increase with the number of merges.
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*
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* A good estimate is to set a @max_merge_size to 1024 for around
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* 1ms runtimes, if your compare function is fast.
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*
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* By default, max_merge_size is set to unlimited.
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**/
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void
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gtk_tim_sort_set_max_merge_size (GtkTimSort *self,
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gsize max_merge_size)
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{
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g_return_if_fail (self != NULL);
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if (max_merge_size == 0)
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max_merge_size = G_MAXSIZE;
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self->max_merge_size = max_merge_size;
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}
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/**
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* gtk_tim_sort_get_progress:
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* @self: a GtkTimSort
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*
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* Does a progress estimate about sort progress, estimates relative
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* to the number of items to sort.
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*
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* Note that this is entirely a progress estimate and does not have
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* a relationship with items put in their correct place.
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* It is also an estimate, so no guarantees are made about accuracy,
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* other than that it will only report 100% completion when it is
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* indeed done sorting.
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*
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* To get a percentage, you need to divide this number by the total
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* number of elements that are being sorted.
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*
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* Returns: Rough guess of sort progress
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**/
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gsize
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gtk_tim_sort_get_progress (GtkTimSort *self)
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{
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#define DEPTH 4
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gsize i;
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gsize last, progress;
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g_return_val_if_fail (self != NULL, 0);
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if (self->pending_runs == 0)
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return 0;
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last = self->run[0].len;
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progress = 0;
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for (i = 1; i < DEPTH + 1 && i < self->pending_runs; i++)
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{
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progress += (DEPTH + 1 - i) * MAX (last, self->run[i].len);
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last = MIN (last, self->run[i].len);
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}
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if (i < DEPTH + 1)
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progress += (DEPTH + 1 - i) * last;
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return progress / DEPTH;
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#undef DEPTH
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}
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#if 1
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#define WIDTH 4
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#include "gtktimsort-impl.c"
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#define WIDTH 8
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#include "gtktimsort-impl.c"
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#define WIDTH 16
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#include "gtktimsort-impl.c"
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#endif
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#define NAME default
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#define WIDTH (self->element_size)
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#include "gtktimsort-impl.c"
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/*
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* gtk_tim_sort_step:
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* @self: a GtkTimSort
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* @out_change: (optional): Return location for changed
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* area. If a change did not cause any changes (for example,
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* if an already sorted array gets sorted), out_change
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* will be set to %NULL and 0.
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*
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* Performs another step in the sorting process. If a
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* step was performed, %TRUE is returned and @out_change is
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* set to the smallest area that contains all changes while
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* sorting.
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*
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* If the data is completely sorted, %FALSE will be
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* returned.
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*
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* Returns: %TRUE if an action was performed
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**/
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gboolean
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gtk_tim_sort_step (GtkTimSort *self,
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GtkTimSortRun *out_change)
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{
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gboolean result;
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g_assert (self);
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switch (self->element_size)
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{
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case 4:
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result = gtk_tim_sort_step_4 (self, out_change);
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break;
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case 8:
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result = gtk_tim_sort_step_8 (self, out_change);
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break;
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case 16:
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result = gtk_tim_sort_step_16 (self, out_change);
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break;
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default:
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result = gtk_tim_sort_step_default (self, out_change);
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break;
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}
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return result;
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}
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