Commit 4333fb96 authored by Rasmus Villemoes's avatar Rasmus Villemoes Committed by Mauro Carvalho Chehab
Browse files

media: lib/sort.c: implement sort() variant taking context argument 



Our list_sort() utility has always supported a context argument that
is passed through to the comparison routine. Now there's a use case
for the similar thing for sort().

This implements sort_r by simply extending the existing sort function
in the obvious way. To avoid code duplication, we want to implement
sort() in terms of sort_r(). The naive way to do that is

static int cmp_wrapper(const void *a, const void *b, const void *ctx)
{
  int (*real_cmp)(const void*, const void*) = ctx;
  return real_cmp(a, b);
}

sort(..., cmp) { sort_r(..., cmp_wrapper, cmp) }

but this would do two indirect calls for each comparison. Instead, do
as is done for the default swap functions - that only adds a cost of a
single easily predicted branch to each comparison call.

Aside from introducing support for the context argument, this also
serves as preparation for patches that will eliminate the indirect
comparison calls in common cases.

Requested-by: default avatarBoris Brezillon <boris.brezillon@collabora.com>

Signed-off-by: default avatarRasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: default avatarBoris Brezillon <boris.brezillon@collabora.com>
Acked-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Tested-by: default avatarPhilipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: default avatarHans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: default avatarMauro Carvalho Chehab <mchehab+samsung@kernel.org>
parent 4843a543

include/linux/sort.h

+5 −0
Original line number Diff line number Diff line
@@ -4,6 +4,11 @@ 


#include <linux/types.h>



void sort_r(void *base, size_t num, size_t size,

	    int (*cmp)(const void *, const void *, const void *),

	    void (*swap)(void *, void *, int),

	    const void *priv);



void sort(void *base, size_t num, size_t size,

	  int (*cmp)(const void *, const void *),

	  void (*swap)(void *, void *, int));

lib/sort.c

+28 −6
Original line number Diff line number Diff line
@@ -144,6 +144,18 @@ static void do_swap(void *a, void *b, size_t size, swap_func_t swap_func) 
		swap_func(a, b, (int)size);

}



typedef int (*cmp_func_t)(const void *, const void *);

typedef int (*cmp_r_func_t)(const void *, const void *, const void *);

#define _CMP_WRAPPER ((cmp_r_func_t)0L)



static int do_cmp(const void *a, const void *b,

		  cmp_r_func_t cmp, const void *priv)

{

	if (cmp == _CMP_WRAPPER)

		return ((cmp_func_t)(priv))(a, b);

	return cmp(a, b, priv);

}



/**

 * parent - given the offset of the child, find the offset of the parent.

 * @i: the offset of the heap element whose parent is sought.  Non-zero.
@@ -171,12 +183,13 @@ static size_t parent(size_t i, unsigned int lsbit, size_t size) 
}



/**

 * sort - sort an array of elements

 * sort_r - sort an array of elements

 * @base: pointer to data to sort

 * @num: number of elements

 * @size: size of each element

 * @cmp_func: pointer to comparison function

 * @swap_func: pointer to swap function or NULL

 * @priv: third argument passed to comparison function

 *

 * This function does a heapsort on the given array.  You may provide

 * a swap_func function if you need to do something more than a memory
@@ -188,9 +201,10 @@ static size_t parent(size_t i, unsigned int lsbit, size_t size) 
 * O(n*n) worst-case behavior and extra memory requirements that make

 * it less suitable for kernel use.

 */

void sort(void *base, size_t num, size_t size,

	  int (*cmp_func)(const void *, const void *),

	  void (*swap_func)(void *, void *, int size))

void sort_r(void *base, size_t num, size_t size,

	    int (*cmp_func)(const void *, const void *, const void *),

	    void (*swap_func)(void *, void *, int size),

	    const void *priv)

{

	/* pre-scale counters for performance */

	size_t n = num * size, a = (num/2) * size;
@@ -238,12 +252,12 @@ void sort(void *base, size_t num, size_t size, 
		 * average, 3/4 worst-case.)

		 */

		for (b = a; c = 2*b + size, (d = c + size) < n;)

			b = cmp_func(base + c, base + d) >= 0 ? c : d;

			b = do_cmp(base + c, base + d, cmp_func, priv) >= 0 ? c : d;

		if (d == n)	/* Special case last leaf with no sibling */

			b = c;



		/* Now backtrack from "b" to the correct location for "a" */

		while (b != a && cmp_func(base + a, base + b) >= 0)

		while (b != a && do_cmp(base + a, base + b, cmp_func, priv) >= 0)

			b = parent(b, lsbit, size);

		c = b;			/* Where "a" belongs */

		while (b != a) {	/* Shift it into place */
@@ -252,4 +266,12 @@ void sort(void *base, size_t num, size_t size, 
		}

	}

}

EXPORT_SYMBOL(sort_r);



void sort(void *base, size_t num, size_t size,

	  int (*cmp_func)(const void *, const void *),

	  void (*swap_func)(void *, void *, int size))

{

	return sort_r(base, num, size, _CMP_WRAPPER, swap_func, cmp_func);

}

EXPORT_SYMBOL(sort);

CRA Git | Maintained and supported by SUSTech CRA and CCSE