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/* ===-- clzsi2.c - Implement __clzsi2 -------------------------------------===
*
* The LLVM Compiler Infrastructure
*
* This file is dual licensed under the MIT and the University of Illinois Open
* Source Licenses. See LICENSE.TXT for details.
*
* ===----------------------------------------------------------------------===
*
* This file implements __clzsi2 for the compiler_rt library.
*
* ===----------------------------------------------------------------------===
*/
#include "int_lib.h"
/* Returns: the number of leading 0-bits */
/* Precondition: a != 0 */
COMPILER_RT_ABI si_int
__clzsi2(si_int a)
{
su_int x = (su_int)a;
si_int t = ((x & 0xFFFF0000) == 0) << 4; /* if (x is small) t = 16 else 0 */
x >>= 16 - t; /* x = [0 - 0xFFFF] */
su_int r = t; /* r = [0, 16] */
/* return r + clz(x) */
t = ((x & 0xFF00) == 0) << 3;
x >>= 8 - t; /* x = [0 - 0xFF] */
r += t; /* r = [0, 8, 16, 24] */
/* return r + clz(x) */
t = ((x & 0xF0) == 0) << 2;
x >>= 4 - t; /* x = [0 - 0xF] */
r += t; /* r = [0, 4, 8, 12, 16, 20, 24, 28] */
/* return r + clz(x) */
t = ((x & 0xC) == 0) << 1;
x >>= 2 - t; /* x = [0 - 3] */
r += t; /* r = [0 - 30] and is even */
/* return r + clz(x) */
/* switch (x)
* {
* case 0:
* return r + 2;
* case 1:
* return r + 1;
* case 2:
* case 3:
* return r;
* }
*/
return r + ((2 - x) & -((x & 2) == 0));
}
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