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