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annotate lwcc/README.txt @ 536:33a59e232a5b

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Fix basic output target to keep lines below 249 characters The line length limiter in the basic output was not properly moving to the next before 249 characters, which is the limit Color Basic can read in an ASCII basic program. Changed the line limiter to 240 from 247 to account for a possible 5 digit number plus a comma and just a bit of extra breathing space.
author William Astle <lost@l-w.ca>
date Thu, 16 Jun 2022 13:55:34 -0600
parents 9e342c4e4b66
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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1 This is the lwcc C compiler for lwtools. It was written using various other
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2 C compilers as guides. Special thanks to the developers of the PCC compiler.
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3 While none of the actual code from PCC was actually used, much of compiler
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4 itself served as a template for creating lwcc.
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7 LIMITATIONS AND DESIGN CHOICES
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8 ==============================
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10 The direct interface to both the compiler proper and the preprocessor is
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11 specifically undefined. Indeed, the preprocessor may, in fact, not be a
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12 separate program at all. Relying on the specific format of the output of the
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13 preprocessor is specifically forbidden even though it is possible to obtain
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14 preprocessed output from the compiler driver. This is provided for debugging
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15 purposes only.
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17 The preprocessor supports variadic macros. It also supports stringification,
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18 and token concatenation but only within a macro expansion. There are
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19 examples online that use the construct "#__LINE__" to get a string version
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20 of the current line number.
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22 The preprocessor defaults to ignoring trigraphs because they are basically a
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23 stupid idea on any current system. They have their place for systems where
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24 creating the nine characters specified by the trigraphs is very difficult or
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25 impossible. It is possible, however, to instruct the preprocessor to decode
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26 trigraph sequences.
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27
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28 The nonstandard "#pragma once" feature is not supported at all. The effect
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29 is easily accomplished using standard macros and conditionals. It is,
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30 therefore, unneeded complexity.
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32 The nonstandard idea of preprocessor assertions is also completely
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33 unsupported. It is just as easy to test predefined macros and such tests are
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34 much more portable.
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36 The preprocessor supports __LINE__, __FILE__, __DATE__, and __TIME__. The
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37 compiler itself supports __func__ as a predefined string constant if
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38 encountered because there is no way for the preprocessor to determine what
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39 function it occurs within. The preprocessor does not define __STDC__,
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40 __STDC_VERSION__, or __STDC_HOSTED__. I have seen no truly useful purpose
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41 for these and since lwcc does not, at this time, conform to any known C
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42 standard, it would be incorrect to define the first two.
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43
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44 The compiler driver may define additional macros depending on its idea of
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45 the context.
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48 RUNTIME INFORMATION
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49 ===================
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50
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51 The compiler driver has a built in base directory where it searches for its
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52 various components as needed. In the discussion below, BASEDIR stands for
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53 that directory.
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55 BASEDIR may be specified by the -B option to the driver. Care must be taken
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56 when doing so, however, because specifying an invalid -B will cause the
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57 compiler to fail completely. It will completely override the built in search
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58 paths for the compiler provided files and programs.
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60 Because BASEDIR is part of the actual compiler, it is not affected by
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61 --sysroot or -isysroot options.
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63 If BASEDIR does not exist, compiler component programs will be searched for
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64 in the standard execution paths. This may lead to incorrect results so it is
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65 important to make certain that the specified BASEDIR exists.
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66
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67 If -B is not specified, the default BASEDIR is
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68 $(PREFIX)/lib/lwcc/$(VERSION)/ where PREFIX is the build prefix from the
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69 Makefile and VERSION is the lwtools version.
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71 The contents of BASEDIR are as follows:
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73 BASEDIR/bin
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75 Various binaries for the parts of the compiler system. Notably, this
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76 includes the preprocessor and compiler proper. The specific names and
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77 contents of this directory cannot be relied upon and these programs should
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78 not be called directly. Ever. Don't do it.
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81 BASEDIR/lib
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83 This directory contains various libraries that provide support for any
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84 portion of the compiler's output. The driver will arrange to pass the
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85 appropriate arguments to the linker to include these as required.
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86
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87 The most notable file in this directory is liblwcc.a wich contains the
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88 support routines for the compiler's code generation. Depending on ABI and
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89 code generation options supported, there may be multiple versions of
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90 liblwcc.a. The driver will arrange for the correct one to be referenced.
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93 BASEDIR/include
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94
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95 This directory contains any C header files that the compiler provides.
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96 Notably, this includes stdint.h, stdarg.h, and setjmp.h as these are
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97 specific to the compiler. The driver will arrange for this directory to be
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98 searched prior to the standard system directories so that these files will
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99 override any present in those directories.
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100