ed25519/amd64-51-30k/sc25519_slide.c

   1 #include "sc25519.h"
   2
   3 void sc25519_slide(signed char r[256], const sc25519 *s, int swindowsize)
   4 {
   5   int i,j,k,b,m=(1<<(swindowsize-1))-1, soplen=256;
   6   unsigned long long sv0 = s->v[0];
   7   unsigned long long sv1 = s->v[1];
   8   unsigned long long sv2 = s->v[2];
   9   unsigned long long sv3 = s->v[3];
  10
  11   /* first put the binary expansion into r  */
  12   for(i=0;i<64;i++) {
  13     r[i] = sv0 & 1;
  14     r[i+64] = sv1 & 1;
  15     r[i+128] = sv2 & 1;
  16     r[i+192] = sv3 & 1;
  17     sv0 >>= 1;
  18     sv1 >>= 1;
  19     sv2 >>= 1;
  20     sv3 >>= 1;
  21   }
  22
  23   /* Making it sliding window */
  24   for (j = 0;j < soplen;++j)
  25   {
  26     if (r[j]) {
  27       for (b = 1;b < soplen - j && b <= 6;++b) {
  28         if (r[j] + (r[j + b] << b) <= m)
  29         {
  30           r[j] += r[j + b] << b; r[j + b] = 0;
  31         }
  32         else if (r[j] - (r[j + b] << b) >= -m)
  33         {
  34           r[j] -= r[j + b] << b;
  35           for (k = j + b;k < soplen;++k)
  36           {
  37             if (!r[k]) {
  38               r[k] = 1;
  39               break;
  40             }
  41             r[k] = 0;
  42           }
  43         }
  44         else if (r[j + b])
  45           break;
  46       }
  47     }
  48   }
  49 }