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[libpng16] Moved OS dependent code from arm/arm_init.c, to allow the included

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implementation of the ARM NEON discovery function to be set at
build-time and provide sample implementations from the current code in the
contrib/arm-neon subdirectory. The __linux__ code has also been changed to
compile and link on Android by using /proc/cpuinfo, and the old linux code
is in contrib/arm-neon/linux-auxv.c.  The new code avoids POSIX and Linux
dependencies apart from opening /proc/cpuinfo and is C90 compliant.
This commit is contained in:
John Bowler 2014-02-16 14:00:06 -06:00 committed by Glenn Randers-Pehrson
parent 38ef9c9779
commit dba54b8888
7 changed files with 437 additions and 121 deletions
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7
ANNOUNCE
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@ -59,6 +59,13 @@ Version 1.6.10beta02 [February 16, 2014]
Moved redefines of png_error(), png_warning(), png_chunk_error(),
and png_chunk_warning() from pngpriv.h to png.h to make them visible
to libpng-calling applications.
Moved OS dependent code from arm/arm_init.c, to allow the included
implementation of the ARM NEON discovery function to be set at
build-time and provide sample implementations from the current code in the
contrib/arm-neon subdirectory. The __linux__ code has also been changed to
compile and link on Android by using /proc/cpuinfo, and the old linux code
is in contrib/arm-neon/linux-auxv.c. The new code avoids POSIX and Linux
dependencies apart from opening /proc/cpuinfo and is C90 compliant.
Send comments/corrections/commendations to png-mng-implement at lists.sf.net
(subscription required; visit

7
CHANGES
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@ -4833,6 +4833,13 @@ Version 1.6.10beta02 [February 16, 2014]
Moved redefines of png_error(), png_warning(), png_chunk_error(),
and png_chunk_warning() from pngpriv.h to png.h to make them visible
to libpng-calling applications.
Moved OS dependent code from arm/arm_init.c, to allow the included
implementation of the ARM NEON discovery function to be set at
build-time and provide sample implementations from the current code in the
contrib/arm-neon subdirectory. The __linux__ code has also been changed to
compile and link on Android by using /proc/cpuinfo, and the old linux code
is in contrib/arm-neon/linux-auxv.c. The new code avoids POSIX and Linux
dependencies apart from opening /proc/cpuinfo and is C90 compliant.
Send comments/corrections/commendations to png-mng-implement at lists.sf.net
(subscription required; visit

143
arm/arm_init.c
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@ -19,132 +19,33 @@
#ifdef PNG_READ_SUPPORTED
#if PNG_ARM_NEON_OPT > 0
#ifdef PNG_ARM_NEON_CHECK_SUPPORTED /* Do run-time checks */
#include <signal.h> /* for sig_atomic_t */
#ifdef __ANDROID__
/* Linux provides access to information about CPU capabilites via
* /proc/self/auxv, however Android blocks this while still claiming to be
* Linux. The Andoid NDK, however, provides appropriate support.
/* WARNING: it is strongly recommended that you do not build libpng with
* run-time checks for CPU features if at all possible. In the case of the ARM
* NEON instructions there is no processor-specific way of detecting the
* presense of the required support, therefore run-time detectioon is extremely
* OS specific.
*
* Documentation: http://www.kandroid.org/ndk/docs/CPU-ARM-NEON.html
* You may set the macro PNG_ARM_NEON_FILE to the file name of file containing
* a fragment of C source code which defines the png_have_neon function. There
* are a number of implementations in contrib/arm-neon, but the only one that
* has partial support is contrib/arm-neon/linux.c - a generic Linux
* implementation which reads /proc/cpufino.
*/
#include <cpu-features.h>
#ifndef PNG_ARM_NEON_FILE
# ifdef __linux__
# define PNG_ARM_NEON_FILE "contrib/arm-neon/linux.c"
# endif
#endif
static int
png_have_neon(png_structp png_ptr)
{
/* This is a whole lot easier than the mess below, however it is probably
* implemented as below, therefore it is better to cache the result (these
* function calls may be slow!)
*/
PNG_UNUSED(png_ptr)
return android_getCpuFamily() == ANDROID_CPU_FAMILY_ARM &&
(android_getCpuFeatures() & ANDROID_CPU_ARM_FEATURE_NEON) != 0;
}
#elif defined(__linux__)
/* The generic __linux__ implementation requires reading /proc/self/auxv and
* looking at each element for one that records NEON capabilities.
*/
#include <unistd.h> /* for POSIX 1003.1 */
#include <errno.h> /* for EINTR */
#ifdef PNG_ARM_NEON_FILE
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <elf.h>
#include <asm/hwcap.h>
#include <signal.h> /* for sig_atomic_t */
static int png_have_neon(png_structp png_ptr);
#include PNG_ARM_NEON_FILE
/* A read call may be interrupted, in which case it returns -1 and sets errno to
* EINTR if nothing was done, otherwise (if something was done) a partial read
* may result.
*/
static size_t
safe_read(png_structp png_ptr, int fd, void *buffer_in, size_t nbytes)
{
size_t ntotal = 0;
char *buffer = png_voidcast(char*, buffer_in);
while (nbytes > 0)
{
unsigned int nread;
int iread;
/* Passing nread > INT_MAX to read is implementation defined in POSIX
* 1003.1, therefore despite the unsigned argument portable code must
* limit the value to INT_MAX!
*/
if (nbytes > INT_MAX)
nread = INT_MAX;
else
nread = (unsigned int)/*SAFE*/nbytes;
iread = read(fd, buffer, nread);
if (iread == -1)
{
/* This is the devil in the details, a read can terminate early with 0
* bytes read because of EINTR, yet it still returns -1 otherwise end
* of file cannot be distinguished.
*/
if (errno != EINTR)
{
png_warning(png_ptr, "/proc read failed");
return 0; /* I.e., a permanent failure */
}
}
else if (iread < 0)
{
/* Not a valid 'read' result: */
png_warning(png_ptr, "OS /proc read bug");
return 0;
}
else if (iread > 0)
{
/* Continue reading until a permanent failure, or EOF */
buffer += iread;
nbytes -= (unsigned int)/*SAFE*/iread;
ntotal += (unsigned int)/*SAFE*/iread;
}
else
return ntotal;
}
return ntotal; /* nbytes == 0 */
}
static int
png_have_neon(png_structp png_ptr)
{
int fd = open("/proc/self/auxv", O_RDONLY);
Elf32_auxv_t aux;
/* Failsafe: failure to open means no NEON */
if (fd == -1)
{
png_warning(png_ptr, "/proc/self/auxv open failed");
return 0;
}
while (safe_read(png_ptr, fd, &aux, sizeof aux) == sizeof aux)
{
if (aux.a_type == AT_HWCAP && (aux.a_un.a_val & HWCAP_NEON) != 0)
{
close(fd);
return 1;
}
}
close(fd);
return 0;
}
#else
/* We don't know how to do a run-time check on this system */
# error "no support for run-time ARM NEON checks"
#endif /* OS checks */
#else /* PNG_ARM_NEON_FILE */
# error "PNG_ARM_NEON_FILE undefined: no support for run-time ARM NEON checks"
#endif /* PNG_ARM_NEON_FILE */
#endif /* PNG_ARM_NEON_CHECK_SUPPORTED */
#ifndef PNG_ALIGNED_MEMORY_SUPPORTED

83
contrib/arm-neon/README Normal file
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@ -0,0 +1,83 @@
OPERATING SYSTEM SPECIFIC ARM NEON DETECTION
--------------------------------------------
Detection of the ability to exexcute ARM NEON on an ARM processor requires
operating system support. (The information is not available in user mode.)
HOW TO USE THIS
---------------
This directory contains C code fragments which can be included in arm/arm_init.c
by setting the macro PNG_ARM_NEON_FILE to the file name in "" or <> at build
time. This setting is not recorded in pnglibconf.h and can be changed simply by
rebuilding arm/arm_init.o with the required macro definition.
For any of this code to be used the ARM NEON code must be enabled and run time
checks must be supported. I.e.:
#if PNG_ARM_NEON_OPT > 0
#ifdef PNG_ARM_NEON_CHECK_SUPPORTED
This is done in a 'configure' build by passing configure the argument:
--enable-arm-neon=check
Apart from the basic Linux implementation in contrib/arm-neon/linux.c this code
is unsupported. That means that it is not even compiled on a regular basis and
may be broken in any given minor release.
FILE FORMAT
-----------
Each file documents its testing status as of the last time it was tested (which
may have been a long time ago):
STATUS: one of:
SUPPORTED: This indicates that the file is included in the regularly
performed test builds and bugs are fixed when discovered.
COMPILED: This indicates that the code did compile at least once. See the
more detailed description for the extent to which the result was
successful.
TESTED: This means the code was fully compiled into the libpng test programs
and these were run at least once.
BUG REPORTS: an email address to which to send reports of problems
The file is a fragment of C code. It should not define any 'extern' symbols;
everything should be static. It must define the function:
static int png_have_neon(png_structp png_ptr);
That function must return 1 if ARM NEON instructions are supported, 0 if not.
It must not execute png_error unless it detects a bug. A png_error will prevent
the reading of the PNG and in the future, writing too.
BUG REPORTS
-----------
If you mail a bug report for any file that is not SUPPORTED there may only be
limited response. Consider fixing it and sending a patch to fix the problem -
this is more likely to result in action.
CONTRIBUTIONS
-------------
You may send contributions of new implementations to
png-mng-implement@sourceforge.net. Please write code in strict C90 C where
possible. Obviously OS dependencies are to be expected. If you submit code you
must have the authors permission and it must have a license that is acceptable
to the current maintainer; in particular that license must permit
redistribution.
Please try to make the contribution a single file and give the file a clear and
unambiguous name that identifies the target OS. If multiple files really are
required put them all in a sub-directory.
You must also be prepared to handle bug reports from users of the code, either
by joining the png-mng-implement mailing list or by providing an email for the
"BUG REPORTS" entry or both. Please make sure that the header of the file
contains the STATUS and BUG REPORTS fields as above.
Please list the OS requirements as precisely as possible. Ideally you should
also list the environment in which the code has been tested and certainly list
any environments where you suspect it might not work.

39
contrib/arm-neon/android-ndk.c Normal file
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@ -0,0 +1,39 @@
/* contrib/arm-neon/android-ndk.c
*
* Copyright (c) 2014 Glenn Randers-Pehrson
* Written by John Bowler, 2014.
* Last changed in libpng 1.6.10 [(PENDING RELEASE)]
*
* This code is released under the libpng license.
* For conditions of distribution and use, see the disclaimer
* and license in png.h
*
* SEE contrib/arm-neon/README before reporting bugs
*
* STATUS: COMPILED, UNTESTED
* BUG REPORTS: png-mng-implement@sourceforge.net
*
* png_have_neon implemented for the Android NDK, see:
*
* Documentation:
* http://www.kandroid.org/ndk/docs/CPU-ARM-NEON.html
* http://code.google.com/p/android/issues/detail?id=49065
*
* NOTE: this requires that libpng is built against the Android NDK and linked
* with an implementation of the Android ARM 'cpu-features' library. The code
* has been compiled only, not linked: no version of the library has been found,
* only the header files exist in the NDK.
*/
#include <cpu-features.h>
static int
png_have_neon(png_structp png_ptr)
{
/* This is a whole lot easier than the linux code, however it is probably
* implemented as below, therefore it is better to cache the result (these
* function calls may be slow!)
*/
PNG_UNUSED(png_ptr)
return android_getCpuFamily() == ANDROID_CPU_FAMILY_ARM &&
(android_getCpuFeatures() & ANDROID_CPU_ARM_FEATURE_NEON) != 0;
}

120
contrib/arm-neon/linux-auxv.c Normal file
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@ -0,0 +1,120 @@
/* contrib/arm-neon/linux-auxv.c
*
* Copyright (c) 2014 Glenn Randers-Pehrson
* Written by Mans Rullgard, 2011.
* Last changed in libpng 1.6.10 [(PENDING RELEASE)]
*
* This code is released under the libpng license.
* For conditions of distribution and use, see the disclaimer
* and license in png.h
*
* SEE contrib/arm-neon/README before reporting bugs
*
* STATUS: COMPILED, TESTED
* BUG REPORTS: png-mng-implement@sourceforge.net
*
* png_have_neon implemented for Linux versions which allow access to
* /proc/self/auxv. This is probably faster, cleaner and safer than the code to
* read /proc/cpuinfo in contrib/arm-neon/linux, however it is yet another piece
* of potentially untested code and has more complex dependencies than the code
* to read cpuinfo.
*
* This generic __linux__ implementation requires reading /proc/self/auxv and
* looking at each element for one that records NEON capabilities.
*/
#include <unistd.h> /* for POSIX 1003.1 */
#include <errno.h> /* for EINTR */
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <elf.h>
#include <asm/hwcap.h>
/* A read call may be interrupted, in which case it returns -1 and sets errno to
* EINTR if nothing was done, otherwise (if something was done) a partial read
* may result.
*/
static size_t
safe_read(png_structp png_ptr, int fd, void *buffer_in, size_t nbytes)
{
size_t ntotal = 0;
char *buffer = png_voidcast(char*, buffer_in);
while (nbytes > 0)
{
unsigned int nread;
int iread;
/* Passing nread > INT_MAX to read is implementation defined in POSIX
* 1003.1, therefore despite the unsigned argument portable code must
* limit the value to INT_MAX!
*/
if (nbytes > INT_MAX)
nread = INT_MAX;
else
nread = (unsigned int)/*SAFE*/nbytes;
iread = read(fd, buffer, nread);
if (iread == -1)
{
/* This is the devil in the details, a read can terminate early with 0
* bytes read because of EINTR, yet it still returns -1 otherwise end
* of file cannot be distinguished.
*/
if (errno != EINTR)
{
png_warning(png_ptr, "/proc read failed");
return 0; /* I.e., a permanent failure */
}
}
else if (iread < 0)
{
/* Not a valid 'read' result: */
png_warning(png_ptr, "OS /proc read bug");
return 0;
}
else if (iread > 0)
{
/* Continue reading until a permanent failure, or EOF */
buffer += iread;
nbytes -= (unsigned int)/*SAFE*/iread;
ntotal += (unsigned int)/*SAFE*/iread;
}
else
return ntotal;
}
return ntotal; /* nbytes == 0 */
}
static int
png_have_neon(png_structp png_ptr)
{
int fd = open("/proc/self/auxv", O_RDONLY);
Elf32_auxv_t aux;
/* Failsafe: failure to open means no NEON */
if (fd == -1)
{
png_warning(png_ptr, "/proc/self/auxv open failed");
return 0;
}
while (safe_read(png_ptr, fd, &aux, sizeof aux) == sizeof aux)
{
if (aux.a_type == AT_HWCAP && (aux.a_un.a_val & HWCAP_NEON) != 0)
{
close(fd);
return 1;
}
}
close(fd);
return 0;
}

159
contrib/arm-neon/linux.c Normal file
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@ -0,0 +1,159 @@
/* contrib/arm-neon/linux.c
*
* Copyright (c) 2014 Glenn Randers-Pehrson
* Written by John Bowler, 2014.
* Last changed in libpng 1.6.10 [(PENDING RELEASE)]
*
* This code is released under the libpng license.
* For conditions of distribution and use, see the disclaimer
* and license in png.h
*
* SEE contrib/arm-neon/README before reporting bugs
*
* STATUS: SUPPORTED
* BUG REPORTS: png-mng-implement@sourceforge.net
*
* png_have_neon implemented for Linux by reading the widely available
* pseudo-file /proc/cpuinfo.
*
* This code is strict ANSI-C and is probably moderately portable, it does
* however use <stdio.h> and assumes that /proc/cpuinfo is never localized.
*/
#include <stdio.h>
static int
png_have_neon(png_structp png_ptr)
{
FILE *f = fopen("/proc/cpuinfo", "rb");
if (f != NULL)
{
/* This is a simple state machine which reads the input byte-by-byte until
* it gets a match on the 'neon' feature or reaches the end of the stream.
*/
static const char ch_feature[] = { 70, 69, 65, 84, 85, 82, 69 };
static const char ch_neon[] = { 78, 69, 79, 78 };
enum
{
StartLine, Feature, Colon, StartTag, Neon, HaveNeon, SkipTag, SkipLine
} state;
int counter;
for (state=StartLine, counter=0;;)
{
int ch = fgetc(f);
if (ch == EOF)
{
/* EOF means error or end-of-file, return false; neon at EOF is
* assumed to be a mistake.
*/
fclose(f);
return 0;
}
switch (state)
{
case StartLine:
/* Match spaces at the start of line */
if (ch <= 32) /* skip control characters and space */
break;
counter=0;
state = Feature;
/* FALL THROUGH */
case Feature:
/* Match 'FEATURE', ASCII case insensitive. */
if ((ch & ~0x40) == ch_feature[counter])
{
if (++counter == (sizeof ch_feature))
state = Colon;
break;
}
/* did not match 'feature' */
state = SkipLine;
/* FALL THROUGH */
case SkipLine:
skipLine:
/* Skip everything until we see linefeed or carriage return */
if (ch != 10 && ch != 13)
break;
state = StartLine;
break;
case Colon:
/* Match any number of space or tab followed by ':' */
if (ch == 32 || ch == 9)
break;
if (ch == 58) /* i.e. ':' */
{
state = StartTag;
break;
}
/* Either a bad line format or a 'feature' prefix followed by
* other characters.
*/
state = SkipLine;
goto skipLine;
case StartTag:
/* Skip space characters before a tag */
if (ch == 32 || ch == 9)
break;
state = Neon;
counter = 0;
/* FALL THROUGH */
case Neon:
/* Look for 'neon' tag */
if ((ch & ~0x40) == ch_neon[counter])
{
if (++counter == (sizeof ch_neon))
state = HaveNeon;
break;
}
state = SkipTag;
/* FALL THROUGH */
case SkipTag:
/* Skip non-space characters */
if (ch == 10 || ch == 13)
state = StartLine;
else if (ch == 32 || ch == 9)
state = StartTag;
break;
case HaveNeon:
/* Have seen a 'neon' prefix, but there must be a space or new
* line character to terminate it.
*/
if (ch == 10 || ch == 13 || ch == 32 || ch == 9)
{
fclose(f);
return 1;
}
state = SkipTag;
break;
default:
png_error(png_ptr, "png_have_neon: internal error (bug)");
}
}
}
else
png_warning(png_ptr, "/proc/cpuinfo open failed");
return 0;
}