lib/sort.c

Source file repositories/reference/linux-study-clean/lib/sort.c

File Facts

System
Linux kernel
Corpus path
lib/sort.c
Extension
.c
Size
11052 bytes
Lines
358
Domain
Kernel Services
Bucket
lib
Inferred role
Kernel Services: exported/initcall integration point
Status
integration implementation candidate

Why This File Exists

Shared kernel service surface used by multiple subsystems, including helpers, cryptography, virtualization support, and async I/O infrastructure.

Dependency Surface

Detected Declarations

Annotated Snippet

struct wrapper {
	cmp_func_t cmp;
	swap_func_t swap;
};

/*
 * The function pointer is last to make tail calls most efficient if the
 * compiler decides not to inline this function.
 */
static void do_swap(void *a, void *b, size_t size, swap_r_func_t swap_func, const void *priv)
{
	if (swap_func == SWAP_WRAPPER) {
		((const struct wrapper *)priv)->swap(a, b, (int)size);
		return;
	}

	if (swap_func == SWAP_WORDS_64)
		swap_words_64(a, b, size);
	else if (swap_func == SWAP_WORDS_32)
		swap_words_32(a, b, size);
	else if (swap_func == SWAP_BYTES)
		swap_bytes(a, b, size);
	else
		swap_func(a, b, (int)size, priv);
}

#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 ((const struct wrapper *)priv)->cmp(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.
 * @lsbit: a precomputed 1-bit mask, equal to "size & -size"
 * @size: size of each element
 *
 * In terms of array indexes, the parent of element j = @i/@size is simply
 * (j-1)/2.  But when working in byte offsets, we can't use implicit
 * truncation of integer divides.
 *
 * Fortunately, we only need one bit of the quotient, not the full divide.
 * @size has a least significant bit.  That bit will be clear if @i is
 * an even multiple of @size, and set if it's an odd multiple.
 *
 * Logically, we're doing "if (i & lsbit) i -= size;", but since the
 * branch is unpredictable, it's done with a bit of clever branch-free
 * code instead.
 */
__attribute_const__ __always_inline
static size_t parent(size_t i, unsigned int lsbit, size_t size)
{
	i -= size;
	i -= size & -(i & lsbit);
	return i / 2;
}

#include <linux/sched.h>

static void __sort_r(void *base, size_t num, size_t size,
		     cmp_r_func_t cmp_func,
		     swap_r_func_t swap_func,
		     const void *priv,
		     bool may_schedule)
{
	/* pre-scale counters for performance */
	size_t n = num * size, a = (num/2) * size;
	const unsigned int lsbit = size & -size;  /* Used to find parent */
	size_t shift = 0;

	if (!a)		/* num < 2 || size == 0 */
		return;

	/* called from 'sort' without swap function, let's pick the default */
	if (swap_func == SWAP_WRAPPER && !((struct wrapper *)priv)->swap)
		swap_func = NULL;

	if (!swap_func) {
		if (is_aligned(base, size, 8))
			swap_func = SWAP_WORDS_64;
		else if (is_aligned(base, size, 4))
			swap_func = SWAP_WORDS_32;
		else
			swap_func = SWAP_BYTES;
	}

Annotation

Implementation Notes