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  1. #include<stdio.h>
  2.  
  3. // unsigned int、桁あふれの判定
  4. //    (unsigned int のサイズは不問)
  5. int isOverflow_uint(unsigned int x, unsigned int y)
  6. {
  7.     #define UI8H  (sizeof(unsigned int) * 8 / 2)
  8.     return
  9.         (1 << UI8H)
  10.             &
  11.         (
  12.             ((x >> UI8H) + (y >> UI8H)) 
  13.                 +
  14.             (
  15.                 (
  16.                     (
  17.                         (x & ((unsigned int)~0 >> UI8H))
  18.                             +
  19.                         (y & ((unsigned int)~0 >> UI8H))
  20.                     )
  21.                         &
  22.                     (1 << UI8H)
  23.                 ) ? 1 : 0
  24.             )
  25.         );
  26. }
  27.  
  28. int main()
  29. {
  30.     unsigned int a, b;
  31.  
  32.     a = 0xFFFFfffe;             // 32bitだとして…
  33.     b = 0x00000001;
  34.     printf("0x%08X + 0x%08X ～ 桁あふれ %s\n", a, b, isOverflow_uint(a, b) ? "する" : "しない");
  35.  
  36.     a = 0xFFFFfffe;
  37.     b = 0x00000002;
  38.     printf("0x%08X + 0x%08X ～ 桁あふれ %s\n", a, b, isOverflow_uint(a, b) ? "する" : "しない");
  39.  
  40.     return 0;
  41. }
Success #stdin #stdout 0s 1832KB
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Standard input is empty
stdout
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0xFFFFFFFE + 0x00000001 ～ 桁あふれ しない
0xFFFFFFFE + 0x00000002 ～ 桁あふれ する
https://ideone.com/UypVGL
language:
C (gcc 8.3)
created:
11 years ago
visibility:
public

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