1.  /* bfs bfr in C
2.   *
3.   * Michal 'GiM' Spadlinski http://gim.org.pl/ gim@@at@@skrzynka@@dot@@pl
4.   *
5.   * drop me a line, if you've made use of that :-)
6.   *
7.   * redistribute under the terms of GPL
8.   */
9.  #ifdef __cplusplus
10.  extern "C" {
11.  #endif
12.  
13.  #define RISC_SUX
14.  
15.  #ifdef RISC_SUX
16.  int bsr (unsigned long int input)
17.  {
18.   asm( "bsr %%eax,%%ebx\n"
19.   "jnz gimskipxorek1\n"
20.   "xor %%eax, %%eax\n"
21.   "dec %%eax\n"
22.   "gimskipxorek1:\n"
23.   :"=b"(input)
24.   :"a"(input));
25.   return input;
26.  }
27.  
28.  int bsf (unsigned long int input)
29.  {
30.   asm( "bsf %%eax,%%ebx\n"
31.   "jnz gimskipxorek2\n"
32.   "xor %%eax, %%eax\n"
33.   "dec %%eax\n"
34.   "gimskipxorek2:\n"
35.   :"=b"(input)
36.   :"a"(input));
37.   return input;
38.  }
39.  
40.  #else
41.  
42.  /* these are my implementations for sux0rz risc processors
43.   * loop unrolled
44.   */
45.  int bsr (unsigned long int input)
46.  {
47.   long int ret=0,v=input;
48.   /* step 1 */
49.   if (v&0xffff0000)
50.   v>>=16, ret=16;
51.   v&=0xffff;
52.   /* step 2 */
53.   if (v&0xff00)
54.   v>>=8, ret+=8;
55.   v&=0xff;
56.   /* step 3 */
57.   if (v&0xf0)
58.   v>>=4, ret+=4;
59.   v&=0xf;
60.   /* step 4 */
61.   if (v&0xc)
62.   v>>=2, ret+=2;
63.   v&=0x3;
64.   if (v&2)
65.   return ret+1;
66.   else if (v&1)
67.   return ret;
68.   else return 0xff;
69.  }
70.  
71.  int bsf (unsigned long int input)
72.  {
73.   long int ret=0,v=input;
74.   /* step 1 */
75.   if (!(v&0xffff))
76.   v>>=16, ret=16;
77.   v&=0xffff;
78.   /* step 2 */
79.   if (!(v&0xff))
80.   v>>=8, ret+=8;
81.   v&=0xff;
82.   /* step 3 */
83.   if (!(v&0xf))
84.   v>>=4, ret+=4;
85.   v&=0xf;
86.   /* step 4 */
87.   if (!(v&0x3))
88.   v>>=2, ret+=2;
89.   v&=0x3;
90.   if (v&1)
91.   return ret;
92.   else if (v&2)
93.   return ret+1;
94.   else return 0xff;
95.  }
96.  #endif
97.  
98.  #ifdef __cplusplus
99.  }
100.  #endif

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