forked from OSchip/llvm-project
74 lines
1.7 KiB
ArmAsm
74 lines
1.7 KiB
ArmAsm
/* ===-- 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 count leading zeros for 32bit arguments.
|
|
*
|
|
* ===----------------------------------------------------------------------===
|
|
*/
|
|
#include "../assembly.h"
|
|
|
|
.syntax unified
|
|
.text
|
|
DEFINE_CODE_STATE
|
|
|
|
.p2align 2
|
|
DEFINE_COMPILERRT_FUNCTION(__clzsi2)
|
|
#ifdef __ARM_FEATURE_CLZ
|
|
clz r0, r0
|
|
JMP(lr)
|
|
#else
|
|
/* Assumption: n != 0 */
|
|
|
|
/*
|
|
* r0: n
|
|
* r1: count of leading zeros in n + 1
|
|
* r2: scratch register for shifted r0
|
|
*/
|
|
mov r1, 1
|
|
|
|
/*
|
|
* Basic block:
|
|
* if ((r0 >> SHIFT) == 0)
|
|
* r1 += SHIFT;
|
|
* else
|
|
* r0 >>= SHIFT;
|
|
* for descending powers of two as SHIFT.
|
|
*/
|
|
|
|
#define BLOCK(shift) \
|
|
lsrs r2, r0, shift; \
|
|
movne r0, r2; \
|
|
addeq r1, shift \
|
|
|
|
BLOCK(16)
|
|
BLOCK(8)
|
|
BLOCK(4)
|
|
BLOCK(2)
|
|
|
|
/*
|
|
* The basic block invariants at this point are (r0 >> 2) == 0 and
|
|
* r0 != 0. This means 1 <= r0 <= 3 and 0 <= (r0 >> 1) <= 1.
|
|
*
|
|
* r0 | (r0 >> 1) == 0 | (r0 >> 1) == 1 | -(r0 >> 1) | 1 - (r0 >> 1)
|
|
* ---+----------------+----------------+------------+--------------
|
|
* 1 | 1 | 0 | 0 | 1
|
|
* 2 | 0 | 1 | -1 | 0
|
|
* 3 | 0 | 1 | -1 | 0
|
|
*
|
|
* The r1's initial value of 1 compensates for the 1 here.
|
|
*/
|
|
sub r0, r1, r0, lsr #1
|
|
|
|
JMP(lr)
|
|
#endif // __ARM_FEATURE_CLZ
|
|
END_COMPILERRT_FUNCTION(__clzsi2)
|
|
|
|
NO_EXEC_STACK_DIRECTIVE
|
|
|