forked from OSchip/llvm-project
58 lines
1.7 KiB
C
58 lines
1.7 KiB
C
/* ===-- 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));
|
|
}
|