54 lines
1.5 KiB
C
54 lines
1.5 KiB
C
|
/* ===-- 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));
|
||
|
|
}
|