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