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  1.     #include <stdio.h>
  2.     #include <limits.h>
  3.  
  4.     #if CHAR_BIT != 8
  5.     #error char is expected to be 8 bits
  6.     #endif
  7.  
  8.     unsigned char RevByte(unsigned char b)
  9.     {
  10.       static const unsigned char t[16] =
  11.       {
  12.         0x0, 0x8, 0x4, 0xC, 0x2, 0xA, 0x6, 0xE,
  13.         0x1, 0x9, 0x5, 0xD, 0x3, 0xB, 0x7, 0xF
  14.       };
  15.       return t[(b >> 4)] | (t[b&0xF] << 4);
  16.     }
  17.  
  18.     void RevBytes(unsigned char* b, size_t c)
  19.     {
  20.       size_t i;
  21.       for (i = 0; i < c / 2; i++)
  22.       {
  23.         unsigned char t = b[i];
  24.         b[i] = RevByte(b[c - 1 - i]);
  25.         b[c - 1 - i] = RevByte(t);
  26.       }
  27.       if (c & 1)
  28.         b[c / 2] = RevByte(b[c / 2]);
  29.     }
  30.  
  31.     int main(void)
  32.     {
  33.       int i;
  34.       unsigned char buf[16] = 
  35.       {
  36.         0x0, 0x8, 0x4, 0xC, 0x2, 0xA, 0x6, 0xE,
  37.         0x1, 0x9, 0x5, 0xD, 0x3, 0xB, 0x7, 0xF
  38.       };
  39.  
  40.       RevBytes(buf, 16);
  41.  
  42.       for (i = 0; i < 16; i++)
  43.         printf("0x%02X ", buf[i]);
  44.       puts("");
  45.  
  46.       return 0;
  47.     }
  48.  
Success #stdin #stdout 0s 1788KB
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stdin
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Standard input is empty
stdout
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0xF0 0xE0 0xD0 0xC0 0xB0 0xA0 0x90 0x80 0x70 0x60 0x50 0x40 0x30 0x20 0x10 0x00
https://ideone.com/LhrJS7
language:
C99 (gcc 8.3)
created:
11 years ago
visibility:
public

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