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  1. #include <stdio.h>
  2.  
  3. unsigned reverse_nibbles(unsigned i) {
  4.   static const unsigned char lut[] = {
  5.     0x00, 0x08, 0x04, 0x0C, 0x02, 0x0A, 0x06, 0x0E, 
  6.     0x01, 0x09, 0x05, 0x0D, 0x03, 0x0B, 0x07, 0x0F, 
  7.     0x80, 0x88, 0x84, 0x8C, 0x82, 0x8A, 0x86, 0x8E, 
  8.     0x81, 0x89, 0x85, 0x8D, 0x83, 0x8B, 0x87, 0x8F, 
  9.     0x40, 0x48, 0x44, 0x4C, 0x42, 0x4A, 0x46, 0x4E, 
  10.     0x41, 0x49, 0x45, 0x4D, 0x43, 0x4B, 0x47, 0x4F, 
  11.     0xC0, 0xC8, 0xC4, 0xCC, 0xC2, 0xCA, 0xC6, 0xCE, 
  12.     0xC1, 0xC9, 0xC5, 0xCD, 0xC3, 0xCB, 0xC7, 0xCF, 
  13.     0x20, 0x28, 0x24, 0x2C, 0x22, 0x2A, 0x26, 0x2E, 
  14.     0x21, 0x29, 0x25, 0x2D, 0x23, 0x2B, 0x27, 0x2F, 
  15.     0xA0, 0xA8, 0xA4, 0xAC, 0xA2, 0xAA, 0xA6, 0xAE, 
  16.     0xA1, 0xA9, 0xA5, 0xAD, 0xA3, 0xAB, 0xA7, 0xAF, 
  17.     0x60, 0x68, 0x64, 0x6C, 0x62, 0x6A, 0x66, 0x6E, 
  18.     0x61, 0x69, 0x65, 0x6D, 0x63, 0x6B, 0x67, 0x6F, 
  19.     0xE0, 0xE8, 0xE4, 0xEC, 0xE2, 0xEA, 0xE6, 0xEE, 
  20.     0xE1, 0xE9, 0xE5, 0xED, 0xE3, 0xEB, 0xE7, 0xEF, 
  21.     0x10, 0x18, 0x14, 0x1C, 0x12, 0x1A, 0x16, 0x1E, 
  22.     0x11, 0x19, 0x15, 0x1D, 0x13, 0x1B, 0x17, 0x1F, 
  23.     0x90, 0x98, 0x94, 0x9C, 0x92, 0x9A, 0x96, 0x9E, 
  24.     0x91, 0x99, 0x95, 0x9D, 0x93, 0x9B, 0x97, 0x9F, 
  25.     0x50, 0x58, 0x54, 0x5C, 0x52, 0x5A, 0x56, 0x5E, 
  26.     0x51, 0x59, 0x55, 0x5D, 0x53, 0x5B, 0x57, 0x5F, 
  27.     0xD0, 0xD8, 0xD4, 0xDC, 0xD2, 0xDA, 0xD6, 0xDE, 
  28.     0xD1, 0xD9, 0xD5, 0xDD, 0xD3, 0xDB, 0xD7, 0xDF, 
  29.     0x30, 0x38, 0x34, 0x3C, 0x32, 0x3A, 0x36, 0x3E, 
  30.     0x31, 0x39, 0x35, 0x3D, 0x33, 0x3B, 0x37, 0x3F, 
  31.     0xB0, 0xB8, 0xB4, 0xBC, 0xB2, 0xBA, 0xB6, 0xBE, 
  32.     0xB1, 0xB9, 0xB5, 0xBD, 0xB3, 0xBB, 0xB7, 0xBF, 
  33.     0x70, 0x78, 0x74, 0x7C, 0x72, 0x7A, 0x76, 0x7E, 
  34.     0x71, 0x79, 0x75, 0x7D, 0x73, 0x7B, 0x77, 0x7F, 
  35.     0xF0, 0xF8, 0xF4, 0xFC, 0xF2, 0xFA, 0xF6, 0xFE, 
  36.     0xF1, 0xF9, 0xF5, 0xFD, 0xF3, 0xFB, 0xF7, 0xFF
  37.   };
  38.   return (lut[(i & 0xFF000000) >> 24] << 24) |
  39.          (lut[(i & 0x00FF0000) >> 16] << 16) |
  40.          (lut[(i & 0x0000FF00) >>  8] <<  8) |
  41.          (lut[ i & 0x000000FF       ]      );
  42. }
  43.  
  44. void print_bits(unsigned i) {
  45.   static char buffer[33];
  46.   int j;
  47.   for (j = 0; j < 32; ++j) {
  48.   	buffer[31 - j] = (i & 1) ? '1' : '0';
  49.     i >>= 1;
  50.   }
  51.   printf("%s\n", buffer);
  52. }
  53.  
  54. int main() {
  55. 	unsigned i[] = { 0x5BC6, 0xAC5C, 0xCAFEBABE };
  56. 	unsigned j;
  57. 	int k;
  58. 	for (k = 0; k < sizeof(i) / sizeof(i[0]); ++k) {
  59. 	  j = reverse_nibbles(i[k]);
  60. 	  print_bits(i[k]);
  61. 	  print_bits(j);
  62. 	  printf("\n");
  63. 	}
  64. 	return 0;
  65. }
Success #stdin #stdout 0s 2292KB
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stdin
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Standard input is empty
stdout
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00000000000000000101101111000110
00000000000000001010110100110110

00000000000000001010110001011100
00000000000000000101001110100011

11001010111111101011101010111110
00110101111101111101010111010111
https://ideone.com/ZIFD6s
language:
C (gcc 8.3)
created:
11 years ago
visibility:
public

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