workloads/faster-lg.c

   1 #include <stdio.h>
   2 #include <stdlib.h>
   3
   4 static int orig_lg(int n)
   5 {
   6         int j, l;
   7
   8         if (n <= 0) return -1;
   9
  10         for (j = n, l = 0; j; j >>= 1) l++;
  11         return l - 1;
  12 }
  13
  14 #define ARGS(a) a
  15
  16 static int lg ARGS((int n));
  17 static int lg(n)
  18    int n;
  19 {
  20         int j;
  21
  22         if (n <= 0) return -1;
  23
  24         j = 0;
  25 #if 1
  26         if (n & 0xFFFF0000) j  = 16, n >>= 16;
  27         if (n & 0x0000FF00) j +=  8, n >>=  8;
  28         if (n & 0x000000F0) j +=  4, n >>=  4;
  29         if (n & 0x0000000C) j +=  2, n >>=  2;
  30         if (n & 0x00000002) j +=  1;
  31 #else
  32         if (n >> 16) j  = 16, n >>= 16;
  33         if (n >>  8) j +=  8, n >>=  8;
  34         if (n >>  4) j +=  4, n >>=  4;
  35         if (n >>  2) j +=  2, n >>=  2;
  36         if (n >>  1) j +=  1;
  37 #endif
  38
  39         return j;
  40 }
  41
  42 int
  43 main(int argc, char **argv)
  44 {
  45         int i = 0, k, l, f;
  46         srandom(1729);
  47
  48         int sum = 0;
  49
  50
  51         for (k = 0; k < 300000000; ++k) {
  52                 int n = k - 10 /*random() % 60*/;
  53
  54 #if 0
  55                 sum += l = orig_lg(n);
  56 #else
  57                 sum += f = lg(n);
  58 #endif
  59
  60 #if 0
  61                 if (l != f)
  62                         printf("Opps, bug at lg(%d) = %d, not %d\n", n, l, f);
  63 #endif
  64         }
  65
  66         printf("sum = %d\n", sum);
  67 }