| 1 | OPERATING SYSTEM SPECIFIC ARM NEON DETECTION
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| 2 | --------------------------------------------
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| 3 |
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| 4 | Detection of the ability to execute ARM NEON on an ARM processor requires
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| 5 | operating system support. (The information is not available in user mode.)
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| 6 |
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| 7 | HOW TO USE THIS
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| 8 | ---------------
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| 9 |
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| 10 | This directory contains C code fragments that can be included in arm/arm_init.c
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| 11 | by setting the macro PNG_ARM_NEON_FILE to the file name in "" or <> at build
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| 12 | time. This setting is not recorded in pnglibconf.h and can be changed simply by
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| 13 | rebuilding arm/arm_init.o with the required macro definition.
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| 14 |
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| 15 | For any of this code to be used the ARM NEON code must be enabled and run time
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| 16 | checks must be supported. I.e.:
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| 17 |
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| 18 | #if PNG_ARM_NEON_OPT > 0
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| 19 | #ifdef PNG_ARM_NEON_CHECK_SUPPORTED
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| 20 |
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| 21 | This is done in a 'configure' build by passing configure the argument:
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| 22 |
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| 23 | --enable-arm-neon=check
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| 24 |
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| 25 | Apart from the basic Linux implementation in contrib/arm-neon/linux.c this code
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| 26 | is unsupported. That means that it is not even compiled on a regular basis and
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| 27 | may be broken in any given minor release.
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| 28 |
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| 29 | FILE FORMAT
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| 30 | -----------
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| 31 |
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| 32 | Each file documents its testing status as of the last time it was tested (which
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| 33 | may have been a long time ago):
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| 34 |
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| 35 | STATUS: one of:
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| 36 | SUPPORTED: This indicates that the file is included in the regularly
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| 37 | performed test builds and bugs are fixed when discovered.
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| 38 | COMPILED: This indicates that the code did compile at least once. See the
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| 39 | more detailed description for the extent to which the result was
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| 40 | successful.
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| 41 | TESTED: This means the code was fully compiled into the libpng test programs
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| 42 | and these were run at least once.
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| 43 |
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| 44 | BUG REPORTS: an email address to which to send reports of problems
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| 45 |
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| 46 | The file is a fragment of C code. It should not define any 'extern' symbols;
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| 47 | everything should be static. It must define the function:
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| 48 |
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| 49 | static int png_have_neon(png_structp png_ptr);
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| 50 |
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| 51 | That function must return 1 if ARM NEON instructions are supported, 0 if not.
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| 52 | It must not execute png_error unless it detects a bug. A png_error will prevent
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| 53 | the reading of the PNG and in the future, writing too.
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| 54 |
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| 55 | BUG REPORTS
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| 56 | -----------
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| 57 |
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| 58 | If you mail a bug report for any file that is not SUPPORTED there may only be
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| 59 | limited response. Consider fixing it and sending a patch to fix the problem -
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| 60 | this is more likely to result in action.
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| 61 |
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| 62 | CONTRIBUTIONS
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| 63 | -------------
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| 64 |
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| 65 | You may send contributions of new implementations to
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| 66 | [email protected]. Please write code in strict C90 C where
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| 67 | possible. Obviously OS dependencies are to be expected. If you submit code you
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| 68 | must have the authors permission and it must have a license that is acceptable
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| 69 | to the current maintainer; in particular that license must permit modification
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| 70 | and redistribution.
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| 71 |
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| 72 | Please try to make the contribution a single file and give the file a clear and
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| 73 | unambiguous name that identifies the target OS. If multiple files really are
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| 74 | required put them all in a sub-directory.
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| 75 |
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| 76 | You must also be prepared to handle bug reports from users of the code, either
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| 77 | by joining the png-mng-implement mailing list or by providing an email for the
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| 78 | "BUG REPORTS" entry or both. Please make sure that the header of the file
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| 79 | contains the STATUS and BUG REPORTS fields as above.
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| 80 |
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| 81 | Please list the OS requirements as precisely as possible. Ideally you should
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| 82 | also list the environment in which the code has been tested and certainly list
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| 83 | any environments where you suspect it might not work.
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