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  1. #include <stdio.h>
  2. #include <stdint.h>
  3.  
  4. typedef union {uint16_t u; int16_t s;} container16;
  5. typedef union {uint32_t u; int32_t s;} container32;
  6.  
  7. int32_t imul(int16_t x, int16_t y) {
  8.     container16 x1, y1;
  9.     container32 z1;
  10.     x1.s = x;
  11.     y1.s = y;
  12.     z1.u = x1.u * y1.u - (1uL<<16)*(y1.u*(x1.s<0)+x1.u*(y1.s<0));
  13.     return z1.s;
  14. }
  15.  
  16. int main() {
  17.     printf("7 * 8 = %d\n", imul(7, 8));
  18.     printf("-7 * 8 = %d\n", imul(-7, 8));
  19.     printf("7 * -8 = %d\n", imul(7, -8));
  20.     printf("-7 * -8 = %d\n", imul(-7, -8));
  21.     return 0;
  22. }
  23.  
Success #stdin #stdout 0s 9424KB
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stdin
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Standard input is empty
stdout
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7 * 8 = 56
-7 * 8 = -56
7 * -8 = -56
-7 * -8 = 56
https://ideone.com/7TE4No
language:
C (gcc 8.3)
created:
7 years ago
visibility:
public

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