1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
|
/* ===-- clzdi2.c - Implement __clzdi2 -------------------------------------===
*
* 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 64bit arguments.
*
* ===----------------------------------------------------------------------===
*/
#include "../assembly.h"
.syntax unified
.text
#if __ARM_ARCH_ISA_THUMB == 2
.thumb
#endif
.p2align 2
#if __ARM_ARCH_ISA_THUMB == 2
DEFINE_COMPILERRT_THUMB_FUNCTION(__clzdi2)
#else
DEFINE_COMPILERRT_FUNCTION(__clzdi2)
#endif
#ifdef __ARM_FEATURE_CLZ
#ifdef __ARMEB__
cmp r0, 0
itee ne
clzne r0, r0
clzeq r0, r1
addeq r0, r0, 32
#else
cmp r1, 0
itee ne
clzne r0, r1
clzeq r0, r0
addeq r0, r0, 32
#endif
JMP(lr)
#else
/* Assumption: n != 0 */
/*
* r0: n
* r1: upper half of n, overwritten after check
* r1: count of leading zeros in n + 1
* r2: scratch register for shifted r0
*/
#ifdef __ARMEB__
cmp r0, 0
moveq r0, r1
#else
cmp r1, 0
movne r0, r1
#endif
movne r1, 1
moveq r1, 33
/*
* 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(__clzdi2)
|
