xref: /openbmc/qemu/util/bufferiszero.c (revision 2b74dd91)
1 /*
2  * Simple C functions to supplement the C library
3  *
4  * Copyright (c) 2006 Fabrice Bellard
5  *
6  * Permission is hereby granted, free of charge, to any person obtaining a copy
7  * of this software and associated documentation files (the "Software"), to deal
8  * in the Software without restriction, including without limitation the rights
9  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
10  * copies of the Software, and to permit persons to whom the Software is
11  * furnished to do so, subject to the following conditions:
12  *
13  * The above copyright notice and this permission notice shall be included in
14  * all copies or substantial portions of the Software.
15  *
16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
21  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
22  * THE SOFTWARE.
23  */
24 #include "qemu/osdep.h"
25 #include "qemu/cutils.h"
26 #include "qemu/bswap.h"
27 #include "host/cpuinfo.h"
28 
29 typedef bool (*biz_accel_fn)(const void *, size_t);
30 
31 static bool buffer_is_zero_int_lt256(const void *buf, size_t len)
32 {
33     uint64_t t;
34     const uint64_t *p, *e;
35 
36     /*
37      * Use unaligned memory access functions to handle
38      * the beginning and end of the buffer.
39      */
40     if (unlikely(len <= 8)) {
41         return (ldl_he_p(buf) | ldl_he_p(buf + len - 4)) == 0;
42     }
43 
44     t = ldq_he_p(buf) | ldq_he_p(buf + len - 8);
45     p = QEMU_ALIGN_PTR_DOWN(buf + 8, 8);
46     e = QEMU_ALIGN_PTR_DOWN(buf + len - 1, 8);
47 
48     /* Read 0 to 31 aligned words from the middle. */
49     while (p < e) {
50         t |= *p++;
51     }
52     return t == 0;
53 }
54 
55 static bool buffer_is_zero_int_ge256(const void *buf, size_t len)
56 {
57     /*
58      * Use unaligned memory access functions to handle
59      * the beginning and end of the buffer.
60      */
61     uint64_t t = ldq_he_p(buf) | ldq_he_p(buf + len - 8);
62     const uint64_t *p = QEMU_ALIGN_PTR_DOWN(buf + 8, 8);
63     const uint64_t *e = QEMU_ALIGN_PTR_DOWN(buf + len - 1, 8);
64 
65     /* Collect a partial block at the tail end. */
66     t |= e[-7] | e[-6] | e[-5] | e[-4] | e[-3] | e[-2] | e[-1];
67 
68     /*
69      * Loop over 64 byte blocks.
70      * With the head and tail removed, e - p >= 30,
71      * so the loop must iterate at least 3 times.
72      */
73     do {
74         if (t) {
75             return false;
76         }
77         t = p[0] | p[1] | p[2] | p[3] | p[4] | p[5] | p[6] | p[7];
78         p += 8;
79     } while (p < e - 7);
80 
81     return t == 0;
82 }
83 
84 #include "host/bufferiszero.c.inc"
85 
86 static biz_accel_fn buffer_is_zero_accel;
87 static unsigned accel_index;
88 
89 bool buffer_is_zero_ool(const void *buf, size_t len)
90 {
91     if (unlikely(len == 0)) {
92         return true;
93     }
94     if (!buffer_is_zero_sample3(buf, len)) {
95         return false;
96     }
97     /* All bytes are covered for any len <= 3.  */
98     if (unlikely(len <= 3)) {
99         return true;
100     }
101 
102     if (likely(len >= 256)) {
103         return buffer_is_zero_accel(buf, len);
104     }
105     return buffer_is_zero_int_lt256(buf, len);
106 }
107 
108 bool buffer_is_zero_ge256(const void *buf, size_t len)
109 {
110     return buffer_is_zero_accel(buf, len);
111 }
112 
113 bool test_buffer_is_zero_next_accel(void)
114 {
115     if (accel_index != 0) {
116         buffer_is_zero_accel = accel_table[--accel_index];
117         return true;
118     }
119     return false;
120 }
121 
122 static void __attribute__((constructor)) init_accel(void)
123 {
124     accel_index = best_accel();
125     buffer_is_zero_accel = accel_table[accel_index];
126 }
127