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/* ===-- ctzsi2.c - Implement __ctzsi2 -------------------------------------===
*
* 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 __ctzsi2 for the compiler_rt library.
*
* ===----------------------------------------------------------------------===
*/
#include "int_lib.h"
/* Returns: the number of trailing 0-bits */
/* Precondition: a != 0 */
COMPILER_RT_ABI si_int
__ctzsi2(si_int a)
{
su_int x = (su_int)a;
si_int t = ((x & 0x0000FFFF) == 0) << 4; /* if (x has no small bits) t = 16 else 0 */
x >>= t; /* x = [0 - 0xFFFF] + higher garbage bits */
su_int r = t; /* r = [0, 16] */
/* return r + ctz(x) */
t = ((x & 0x00FF) == 0) << 3;
x >>= t; /* x = [0 - 0xFF] + higher garbage bits */
r += t; /* r = [0, 8, 16, 24] */
/* return r + ctz(x) */
t = ((x & 0x0F) == 0) << 2;
x >>= t; /* x = [0 - 0xF] + higher garbage bits */
r += t; /* r = [0, 4, 8, 12, 16, 20, 24, 28] */
/* return r + ctz(x) */
t = ((x & 0x3) == 0) << 1;
x >>= t;
x &= 3; /* x = [0 - 3] */
r += t; /* r = [0 - 30] and is even */
/* return r + ctz(x) */
/* The branch-less return statement below is equivalent
* to the following switch statement:
* switch (x)
* {
* case 0:
* return r + 2;
* case 2:
* return r + 1;
* case 1:
* case 3:
* return r;
* }
*/
return r + ((2 - (x >> 1)) & -((x & 1) == 0));
}
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