1 /* Copyright (C) 2012-2014 Free Software Foundation, Inc.
2 Contributed by Richard Henderson <rth@redhat.com>.
3
4 This file is part of the GNU Atomic Library (libatomic).
5
6 Libatomic is free software; you can redistribute it and/or modify it
7 under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 3 of the License, or
9 (at your option) any later version.
10
11 Libatomic is distributed in the hope that it will be useful, but WITHOUT ANY
12 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
13 FOR A PARTICULAR PURPOSE. See the GNU General Public License for
14 more details.
15
16 Under Section 7 of GPL version 3, you are granted additional
17 permissions described in the GCC Runtime Library Exception, version
18 3.1, as published by the Free Software Foundation.
19
20 You should have received a copy of the GNU General Public License and
21 a copy of the GCC Runtime Library Exception along with this program;
22 see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 <http://www.gnu.org/licenses/>. */
24
25 #include <libatomic_i.h>
26 #include <arm-config.h>
27
28
29 /* When using STREX to implement sub-word exchange, we can do much better
30 than the compiler by using the APSR.GE and APSR.C flags. */
31
32 #if !DONE && HAVE_STREX && !HAVE_STREXBH && N == 2
33 UTYPE
SIZE(libat_exchange)34 SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel)
35 {
36 UWORD t1, t2;
37 UTYPE oldval;
38
39 __atomic_thread_fence (__ATOMIC_SEQ_CST);
40
41 /* In the N=2 case, there are only two cases for MPTR: mptr % 4 == {0,2}.
42 Rather than computing a variable shift for this, we can store the one
43 bit of misalignment in the carry flag, and use conditional constant
44 shifts instead. This saves a register. */
45 #ifdef __ARMEB__
46 # define HI "cc" /* iff value is in high half */
47 # define LO "cs" /* iff value is in low half */
48 #else
49 # define HI "cs"
50 # define LO "cc"
51 #endif
52
53 asm volatile (
54 "lsrs %[t2],%[ptr],#2\n" /* carry = mptr & 2 */
55 " bic %[ptr],%[ptr],#3\n" /* align mptr */
56 " itt "HI"\n"
57 " lsl"HI" %[t1],%[t1],#16\n" /* shift mask into place */
58 " lsl"HI" %[new],%[new],#16\n" /* shift newval into place */
59 " uadd16 %[t1],%[t1],%[t1]\n" /* copy mask into APSR.GE */
60 "0: ldrex %[t2],[%[ptr]]\n"
61 " ite "LO"\n"
62 " uxth"LO" %[old],%[t2]\n" /* return old value */
63 " uxth"HI" %[old],%[t2], ror #16\n"
64 " sel %[t1],%[new],%[t2]\n" /* merge newval */
65 " strex %[t2],%[t1],[%[ptr]]\n"
66 " tst %[t2],%[t2]\n" /* dont clobber carry */
67 " bne 0b"
68 : [old] "=&r"(oldval), [t1] "=&r"(t1), [t2] "=&r"(t2),
69 [ptr] "+r"(mptr), [new] "+r"(newval)
70 : "1"(0xffff)
71 : "memory");
72
73 __atomic_thread_fence (__ATOMIC_SEQ_CST);
74
75 return oldval;
76 }
77
78 #define DONE 1
79 #endif /* !HAVE_STREXBH && N == 2 */
80
81
82 #if !DONE && HAVE_STREX && !HAVE_STREXBH && N == 1
83 UTYPE
SIZE(libat_exchange)84 SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel)
85 {
86 UWORD *wptr, woldval, wnewval, shift, mask, t1, t2;
87
88 __atomic_thread_fence (__ATOMIC_SEQ_CST);
89
90 wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE);
91 shift = (((uintptr_t)mptr % WORDSIZE) * CHAR_BIT) ^ INVERT_MASK_1;
92 mask = MASK_1 << shift;
93 wnewval = newval << shift;
94
95 asm volatile (
96 "uadd8 %[t1],%[t1],%[t1]\n" /* move mask to APSR.GE */
97 "0: ldrex %[old],[%[wptr]]\n"
98 " sel %[t1],%[new],%[old]\n" /* merge newval */
99 " strex %[t2],%[t1],[%[wptr]]\n"
100 " cmp %[t2],#0\n"
101 " bne 0b"
102 : [old] "=&r"(woldval), [t1] "=&r"(t1), [t2] "=&r"(t2)
103 : [new] "r"(wnewval), [wptr] "r"(wptr), "1"(mask)
104 : "memory");
105
106 __atomic_thread_fence (__ATOMIC_SEQ_CST);
107
108 return woldval >> shift;
109 }
110
111 #define DONE 1
112 #endif /* !HAVE_STREXBH && N == 1 */
113
114 #include "../../exch_n.c"
115