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  1. #include <stdio.h>
  2. #include <stdlib.h>
  3.  
  4. void* AllocateLargestFreeBlock(size_t* Size)
  5. {
  6.   size_t s0, s1;
  7.   void* p;
  8.  
  9.   s0 = ~(size_t)0 ^ (~(size_t)0 >> 1);
  10.  
  11.   while (s0 && (p = malloc(s0)) == NULL)
  12.     s0 >>= 1;
  13.  
  14.   if (p)
  15.     free(p);
  16.  
  17.   s1 = s0 >> 1;
  18.  
  19.   while (s1)
  20.   {
  21.     if ((p = malloc(s0 + s1)) != NULL)
  22.     {
  23.       s0 += s1;
  24.       free(p);
  25.     }
  26.     s1 >>= 1;
  27.   }
  28.  
  29.   while (s0 && (p = malloc(s0)) == NULL)
  30.     s0 ^= s0 & -s0;
  31.  
  32.   *Size = s0;
  33.   return p;
  34. }
  35.  
  36. size_t GetFreeSize(void)
  37. {
  38.   size_t total = 0;
  39.   void* pFirst = NULL;
  40.   void* pLast = NULL;
  41.  
  42.   for (;;)
  43.   {
  44.     size_t largest;
  45.     void* p = AllocateLargestFreeBlock(&largest);
  46.  
  47.     if (largest < sizeof(void*))
  48.     {
  49.       if (p != NULL)
  50.         free(p);
  51.       break;
  52.     }
  53.  
  54.     *(void**)p = NULL;
  55.  
  56.     total += largest;
  57.  
  58.     if (pFirst == NULL)
  59.       pFirst = p;
  60.  
  61.     if (pLast != NULL)
  62.       *(void**)pLast = p;
  63.  
  64.     pLast = p;
  65.   }
  66.  
  67.   while (pFirst != NULL)
  68.   {
  69.     void* p = *(void**)pFirst;
  70.     free(pFirst);
  71.     pFirst = p;
  72.   }
  73.  
  74.   return total;
  75. }
  76.  
  77. int main(void)
  78. {
  79.   printf("Total free: %zu\n", GetFreeSize());
  80.   printf("Total free: %zu\n", GetFreeSize());
  81.   printf("Total free: %zu\n", GetFreeSize());
  82.   printf("Total free: %zu\n", GetFreeSize());
  83.   printf("Total free: %zu\n", GetFreeSize());
  84.   return 0;
  85. }
  86.  
Success #stdin #stdout 0.02s 2744KB
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stdin
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Standard input is empty
stdout
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Total free: 266677120
Total free: 266673024
Total free: 266673024
Total free: 266673024
Total free: 266673024
https://ideone.com/V6HUfF
language:
C99 (gcc 8.3)
created:
11 years ago
visibility:
public

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