1/* ===-- clzsi2.c - Implement __clzsi2 -------------------------------------===
2 *
3 *      	       The LLVM Compiler Infrastructure
4 *
5 * This file is distributed under the University of Illinois Open Source
6 * License. See LICENSE.TXT for details.
7 *
8 * ===----------------------------------------------------------------------===
9 *
10 * This file implements __clzsi2 for the compiler_rt library.
11 *
12 * ===----------------------------------------------------------------------===
13 */
14
15#include "int_lib.h"
16
17/* Returns: the number of leading 0-bits */
18
19/* Precondition: a != 0 */
20
21si_int
22__clzsi2(si_int a)
23{
24    su_int x = (su_int)a;
25    si_int t = ((x & 0xFFFF0000) == 0) << 4;  /* if (x is small) t = 16 else 0 */
26    x >>= 16 - t;      /* x = [0 - 0xFFFF] */
27    su_int r = t;       /* r = [0, 16] */
28    /* return r + clz(x) */
29    t = ((x & 0xFF00) == 0) << 3;
30    x >>= 8 - t;       /* x = [0 - 0xFF] */
31    r += t;            /* r = [0, 8, 16, 24] */
32    /* return r + clz(x) */
33    t = ((x & 0xF0) == 0) << 2;
34    x >>= 4 - t;       /* x = [0 - 0xF] */
35    r += t;            /* r = [0, 4, 8, 12, 16, 20, 24, 28] */
36    /* return r + clz(x) */
37    t = ((x & 0xC) == 0) << 1;
38    x >>= 2 - t;       /* x = [0 - 3] */
39    r += t;            /* r = [0 - 30] and is even */
40    /* return r + clz(x) */
41/*     switch (x)
42 *     {
43 *     case 0:
44 *         return r + 2;
45 *     case 1:
46 *         return r + 1;
47 *     case 2:
48 *     case 3:
49 *         return r;
50 *     }
51 */
52    return r + ((2 - x) & -((x & 2) == 0));
53}
54