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  1. #include <stdio.h>
  2. #include <string.h>
  3.  
  4. void MulBytesBy10(unsigned char* buf, size_t cnt)
  5. {
  6.   unsigned carry = 0;
  7.   while (cnt--)
  8.   {
  9.     carry += 10 * *buf;
  10.     *buf++ = carry & 0xFF;
  11.     carry >>= 8;
  12.   }
  13. }
  14.  
  15. void AddDigitToBytes(unsigned char* buf, size_t cnt, unsigned char digit)
  16. {
  17.   unsigned carry = digit;
  18.   while (cnt-- && carry)
  19.   {
  20.     carry += *buf;
  21.     *buf++ = carry & 0xFF;
  22.     carry >>= 8;
  23.   }
  24. }
  25.  
  26. void DecimalIntegerStringToBytes(unsigned char* buf, size_t cnt, const char* str)
  27. {
  28.   memset(buf, 0, cnt);
  29.  
  30.   while (*str != '\0')
  31.   {
  32.     MulBytesBy10(buf, cnt);
  33.     AddDigitToBytes(buf, cnt, *str++ - '0');
  34.   }
  35. }
  36.  
  37. void PrintBytesHex(const unsigned char* buf, size_t cnt)
  38. {
  39.   size_t i;
  40.   for (i = 0; i < cnt; i++)
  41.     printf("%02X", buf[cnt - 1 - i]);
  42. }
  43.  
  44. int main(void)
  45. {
  46.   unsigned char buf[16];
  47.  
  48.   DecimalIntegerStringToBytes(buf, sizeof buf, "664813035583918006462745898431981286737635929725");
  49.  
  50.   PrintBytesHex(buf, sizeof buf); puts("");
  51.  
  52.   return 0;
  53. }
  54.  
Success #stdin #stdout 0s 5392KB
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346C773479735F4834735F6233336E7D
https://ideone.com/TFmpxB
language:
C99 (gcc 8.3)
created:
1 year ago
visibility:
public

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