src/lib/clog2.c

   1 #undef DEBUG_LOG2
   2
   3 #ifdef DEBUG_LOG2
   4 #include <console/console.h>
   5 #endif
   6
   7 #include <lib.h>
   8
   9 /* Assume 8 bits per byte */
  10 #define CHAR_BIT 8
  11
  12 unsigned long log2(unsigned long x)
  13 {
  14         // assume 8 bits per byte.
  15         unsigned long i = 1ULL << (sizeof(x)* CHAR_BIT - 1ULL);
  16         unsigned long pow = sizeof(x) * CHAR_BIT - 1ULL;
  17
  18         if (! x) {
  19 #ifdef DEBUG_LOG2
  20                 printk(BIOS_WARNING, "%s called with invalid parameter of 0\n",
  21                         __func__);
  22 #endif
  23                 return -1;
  24         }
  25         for(; i > x; i >>= 1, pow--)
  26                 ;
  27
  28         return pow;
  29 }