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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0
 /*
  * A fast, small, non-recursive O(n log n) sort for the Linux kernel
  *
  * This performs n*log2(n) + 0.37*n + o(n) comparisons on average,
  * and 1.5*n*log2(n) + O(n) in the (very contrived) worst case.
  *
  * Glibc qsort() manages n*log2(n) - 1.26*n for random inputs (1.63*n
  * better) at the expense of stack usage and much larger code to avoid
  * quicksort's O(n^2) worst case.
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/types.h>
 #include <linux/export.h>
 #include <linux/sort.h>
 
 /**
  * is_aligned - is this pointer & size okay for word-wide copying?
  * @base: pointer to data
  * @size: size of each element
  * @align: required alignment (typically 4 or 8)
  *
  * Returns true if elements can be copied using word loads and stores.
  * The size must be a multiple of the alignment, and the base address must
  * be if we do not have CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS.
  *
  * For some reason, gcc doesn't know to optimize "if (a & mask || b & mask)"
  * to "if ((a | b) & mask)", so we do that by hand.
  */
 __attribute_const__ __always_inline
 static bool is_aligned(const void *base, size_t size, unsigned char align)
 {
     unsigned char lsbits = (unsigned char)size;
 
     (void)base;
 #ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
     lsbits |= (unsigned char)(uintptr_t)base;
 #endif
     return (lsbits & (align - 1)) == 0;
 }
 
 /**
  * swap_words_32 - swap two elements in 32-bit chunks
  * @a: pointer to the first element to swap
  * @b: pointer to the second element to swap
  * @n: element size (must be a multiple of 4)
  *
  * Exchange the two objects in memory.  This exploits base+index addressing,
  * which basically all CPUs have, to minimize loop overhead computations.
  *
  * For some reason, on x86 gcc 7.3.0 adds a redundant test of n at the
  * bottom of the loop, even though the zero flag is still valid from the
  * subtract (since the intervening mov instructions don't alter the flags).
  * Gcc 8.1.0 doesn't have that problem.
  */
 static void swap_words_32(void *a, void *b, size_t n)
 {
     do {
         u32 t = *(u32 *)(a + (n -= 4));
         *(u32 *)(a + n) = *(u32 *)(b + n);
         *(u32 *)(b + n) = t;
     } while (n);
 }
 
 /**
  * swap_words_64 - swap two elements in 64-bit chunks
  * @a: pointer to the first element to swap
  * @b: pointer to the second element to swap
  * @n: element size (must be a multiple of 8)
  *
  * Exchange the two objects in memory.  This exploits base+index
  * addressing, which basically all CPUs have, to minimize loop overhead
  * computations.
  *
  * We'd like to use 64-bit loads if possible.  If they're not, emulating
  * one requires base+index+4 addressing which x86 has but most other
  * processors do not.  If CONFIG_64BIT, we definitely have 64-bit loads,
  * but it's possible to have 64-bit loads without 64-bit pointers (e.g.
  * x32 ABI).  Are there any cases the kernel needs to worry about?
  */
 static void swap_words_64(void *a, void *b, size_t n)
 {
     do {
 #ifdef CONFIG_64BIT
         u64 t = *(u64 *)(a + (n -= 8));
         *(u64 *)(a + n) = *(u64 *)(b + n);
         *(u64 *)(b + n) = t;
 #else
         /* Use two 32-bit transfers to avoid base+index+4 addressing */
         u32 t = *(u32 *)(a + (n -= 4));
         *(u32 *)(a + n) = *(u32 *)(b + n);
         *(u32 *)(b + n) = t;
 
         t = *(u32 *)(a + (n -= 4));
         *(u32 *)(a + n) = *(u32 *)(b + n);
         *(u32 *)(b + n) = t;
 #endif
     } while (n);
 }
 
 /**
  * swap_bytes - swap two elements a byte at a time
  * @a: pointer to the first element to swap
  * @b: pointer to the second element to swap
  * @n: element size
  *
  * This is the fallback if alignment doesn't allow using larger chunks.
  */
 static void swap_bytes(void *a, void *b, size_t n)
 {
     do {
         char t = ((char *)a)[--n];
         ((char *)a)[n] = ((char *)b)[n];
         ((char *)b)[n] = t;
     } while (n);
 }
 
 /*
  * The values are arbitrary as long as they can't be confused with
  * a pointer, but small integers make for the smallest compare
  * instructions.
  */
 #define SWAP_WORDS_64 (swap_r_func_t)0
 #define SWAP_WORDS_32 (swap_r_func_t)1
 #define SWAP_BYTES    (swap_r_func_t)2
 #define SWAP_WRAPPER  (swap_r_func_t)3
 
 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;
 }
 
 /**
  * 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
  * copy (e.g. fix up pointers or auxiliary data), but the built-in swap
  * avoids a slow retpoline and so is significantly faster.
  *
  * Sorting time is O(n log n) both on average and worst-case. While
  * quicksort is slightly faster on average, it suffers from exploitable
  * O(n*n) worst-case behavior and extra memory requirements that make
  * it less suitable for kernel use.
  */
 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)
 {
     /* pre-scale counters for performance */
     size_t n = num * size, a = (num/2) * size;
     const unsigned int lsbit = size & -size;  /* Used to find parent */
 
     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;
     }
 
     /*
      * Loop invariants:
      * 1. elements [a,n) satisfy the heap property (compare greater than
      *    all of their children),
      * 2. elements [n,num*size) are sorted, and
      * 3. a <= b <= c <= d <= n (whenever they are valid).
      */
     for (;;) {
         size_t b, c, d;
 
         if (a)          /* Building heap: sift down --a */
             a -= size;
         else if (n -= size) /* Sorting: Extract root to --n */
             do_swap(base, base + n, size, swap_func, priv);
         else            /* Sort complete */
             break;
 
         /*
          * Sift element at "a" down into heap.  This is the
          * "bottom-up" variant, which significantly reduces
          * calls to cmp_func(): we find the sift-down path all
          * the way to the leaves (one compare per level), then
          * backtrack to find where to insert the target element.
          *
          * Because elements tend to sift down close to the leaves,
          * this uses fewer compares than doing two per level
          * on the way down.  (A bit more than half as many on
          * average, 3/4 worst-case.)
          */
         for (b = a; c = 2*b + size, (d = c + size) < n;)
             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 && 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 */
             b = parent(b, lsbit, size);
             do_swap(base + b, base + c, size, swap_func, priv);
         }
     }
 }
 EXPORT_SYMBOL(sort_r);
 
 void sort(void *base, size_t num, size_t size,
       cmp_func_t cmp_func,
       swap_func_t swap_func)
 {
     struct wrapper w = {
         .cmp  = cmp_func,
         .swap = swap_func,
     };
 
     return sort_r(base, num, size, _CMP_WRAPPER, SWAP_WRAPPER, &w);
 }
 EXPORT_SYMBOL(sort);

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