FFmpeg
blockdsp.c
Go to the documentation of this file.
1 /*
2  * Copyright (c) 2002 Brian Foley
3  * Copyright (c) 2002 Dieter Shirley
4  * Copyright (c) 2003-2004 Romain Dolbeau <romain@dolbeau.org>
5  *
6  * This file is part of FFmpeg.
7  *
8  * FFmpeg is free software; you can redistribute it and/or
9  * modify it under the terms of the GNU Lesser General Public
10  * License as published by the Free Software Foundation; either
11  * version 2.1 of the License, or (at your option) any later version.
12  *
13  * FFmpeg is distributed in the hope that it will be useful,
14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16  * Lesser General Public License for more details.
17  *
18  * You should have received a copy of the GNU Lesser General Public
19  * License along with FFmpeg; if not, write to the Free Software
20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
21  */
22 
23 #include "config.h"
24 
25 #include <string.h>
26 
27 #include "libavutil/attributes.h"
28 #include "libavutil/cpu.h"
29 #include "libavutil/mem.h"
30 #include "libavutil/ppc/cpu.h"
32 
33 #include "libavcodec/blockdsp.h"
34 
35 /* ***** WARNING ***** WARNING ***** WARNING ***** */
36 /*
37  * clear_blocks_dcbz32_ppc will not work properly on PowerPC processors with
38  * a cache line size not equal to 32 bytes. Fortunately all processors used
39  * by Apple up to at least the 7450 (AKA second generation G4) use 32-byte
40  * cache lines. This is due to the use of the 'dcbz' instruction. It simply
41  * clears a single cache line to zero, so you need to know the cache line
42  * size to use it! It's absurd, but it's fast...
43  *
44  * update 24/06/2003: Apple released the G5 yesterday, with a PPC970.
45  * cache line size: 128 bytes. Oups.
46  * The semantics of dcbz was changed, it always clears 32 bytes. So the function
47  * below will work, but will be slow. So I fixed check_dcbz_effect to use dcbzl,
48  * which is defined to clear a cache line (as dcbz before). So we can still
49  * distinguish, and use dcbz (32 bytes) or dcbzl (one cache line) as required.
50  *
51  * see <http://developer.apple.com/technotes/tn/tn2087.html>
52  * and <http://developer.apple.com/technotes/tn/tn2086.html>
53  */
54 static void clear_blocks_dcbz32_ppc(int16_t *blocks)
55 {
56  register int misal = (unsigned long) blocks & 0x00000010, i = 0;
57 
58  if (misal) {
59  ((unsigned long *) blocks)[0] = 0L;
60  ((unsigned long *) blocks)[1] = 0L;
61  ((unsigned long *) blocks)[2] = 0L;
62  ((unsigned long *) blocks)[3] = 0L;
63  i += 16;
64  }
65  for (; i < sizeof(int16_t) * 6 * 64 - 31; i += 32)
66  __asm__ volatile ("dcbz %0,%1" :: "b" (blocks), "r" (i) : "memory");
67  if (misal) {
68  ((unsigned long *) blocks)[188] = 0L;
69  ((unsigned long *) blocks)[189] = 0L;
70  ((unsigned long *) blocks)[190] = 0L;
71  ((unsigned long *) blocks)[191] = 0L;
72  i += 16;
73  }
74 }
75 
76 /* Same as above, when dcbzl clears a whole 128 bytes cache line
77  * i.e. the PPC970 AKA G5. */
78 static void clear_blocks_dcbz128_ppc(int16_t *blocks)
79 {
80 #if HAVE_DCBZL
81  register int misal = (unsigned long) blocks & 0x0000007f, i = 0;
82 
83  if (misal) {
84  /* We could probably also optimize this case,
85  * but there's not much point as the machines
86  * aren't available yet (2003-06-26). */
87  memset(blocks, 0, sizeof(int16_t) * 6 * 64);
88  } else {
89  for (; i < sizeof(int16_t) * 6 * 64; i += 128)
90  __asm__ volatile ("dcbzl %0,%1" :: "b" (blocks), "r" (i) : "memory");
91  }
92 #else
93  memset(blocks, 0, sizeof(int16_t) * 6 * 64);
94 #endif
95 }
96 
97 /* Check dcbz report how many bytes are set to 0 by dcbz. */
98 /* update 24/06/2003: Replace dcbz by dcbzl to get the intended effect
99  * (Apple "fixed" dcbz). Unfortunately this cannot be used unless the
100  * assembler knows about dcbzl ... */
101 static long check_dcbzl_effect(void)
102 {
103  long count = 0;
104 #if HAVE_DCBZL
105  register char *fakedata = av_malloc(1024);
106  register char *fakedata_middle;
107  register long zero = 0, i = 0;
108 
109  if (!fakedata)
110  return 0L;
111 
112  fakedata_middle = fakedata + 512;
113 
114  memset(fakedata, 0xFF, 1024);
115 
116  /* Below the constraint "b" seems to mean "address base register"
117  * in gcc-3.3 / RS/6000 speaks. Seems to avoid using r0, so.... */
118  __asm__ volatile ("dcbzl %0, %1" :: "b" (fakedata_middle), "r" (zero));
119 
120  for (i = 0; i < 1024; i++)
121  if (fakedata[i] == (char) 0)
122  count++;
123 
124  av_free(fakedata);
125 #endif
126 
127  return count;
128 }
129 
130 #if HAVE_ALTIVEC
131 static void clear_block_altivec(int16_t *block)
132 {
133  LOAD_ZERO;
134  vec_st(zero_s16v, 0, block);
135  vec_st(zero_s16v, 16, block);
136  vec_st(zero_s16v, 32, block);
137  vec_st(zero_s16v, 48, block);
138  vec_st(zero_s16v, 64, block);
139  vec_st(zero_s16v, 80, block);
140  vec_st(zero_s16v, 96, block);
141  vec_st(zero_s16v, 112, block);
142 }
143 #endif /* HAVE_ALTIVEC */
144 
146 {
147  // common optimizations whether AltiVec is available or not
148  switch (check_dcbzl_effect()) {
149  case 32:
151  break;
152  case 128:
154  break;
155  default:
156  break;
157  }
158 
159 #if HAVE_ALTIVEC
161  return;
162 
163  c->clear_block = clear_block_altivec;
164 #endif /* HAVE_ALTIVEC */
165 }
Memory handling functions.
void(* clear_block)(int16_t *block)
Definition: blockdsp.h:36
static long check_dcbzl_effect(void)
Definition: blockdsp.c:101
#define LOAD_ZERO
Definition: util_altivec.h:45
Macro definitions for various function/variable attributes.
The exact code depends on how similar the blocks are and how related they are to the block
#define av_cold
Definition: attributes.h:82
#define av_malloc(s)
Undefined Behavior In the C some operations are like signed integer dereferencing freed accessing outside allocated Undefined Behavior must not occur in a C it is not safe even if the output of undefined operations is unused The unsafety may seem nit picking but Optimizing compilers have in fact optimized code on the assumption that no undefined Behavior occurs Optimizing code based on wrong assumptions can and has in some cases lead to effects beyond the output of computations The signed integer overflow problem in speed critical code Code which is highly optimized and works with signed integers sometimes has the problem that often the output of the computation does not c
Definition: undefined.txt:32
#define i(width, name, range_min, range_max)
Definition: cbs_h2645.c:259
void(* clear_blocks)(int16_t *blocks)
Definition: blockdsp.h:37
#define PPC_ALTIVEC(flags)
Definition: cpu.h:25
#define zero
Definition: regdef.h:64
GLsizei count
Definition: opengl_enc.c:108
static void clear_blocks_dcbz128_ppc(int16_t *blocks)
Definition: blockdsp.c:78
#define L(x)
Definition: vp56_arith.h:36
static void clear_blocks_dcbz32_ppc(int16_t *blocks)
Definition: blockdsp.c:54
int av_get_cpu_flags(void)
Return the flags which specify extensions supported by the CPU.
Definition: cpu.c:93
Contains misc utility macros and inline functions.
#define zero_s16v
Definition: util_altivec.h:50
av_cold void ff_blockdsp_init_ppc(BlockDSPContext *c)
Definition: blockdsp.c:145
#define av_free(p)