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Diffstat (limited to 'subx/001help.cc')
| -rw-r--r-- | subx/001help.cc | 220 |
1 files changed, 220 insertions, 0 deletions
diff --git a/subx/001help.cc b/subx/001help.cc new file mode 100644 index 00000000..d20d8144 --- /dev/null +++ b/subx/001help.cc @@ -0,0 +1,220 @@ +//: Everything this project/binary supports. +//: This should give you a sense for what to look forward to in later layers. + +:(before "End Commandline Parsing") +if (argc != 1) { + //: this is the functionality later layers will provide + // currently no automated tests for commandline arg parsing + return 1; +} + +//: Support for option parsing. +//: Options always begin with '--' and are always the first arguments. An +//: option will never follow a non-option. +:(before "End Commandline Parsing") +char** arg = &argv[1]; +while (argc > 1 && starts_with(*arg, "--")) { + if (false) + ; // no-op branch just so any further additions can consistently always start with 'else' + // End Commandline Options(*arg) + else + cerr << "skipping unknown option " << *arg << '\n'; + --argc; ++argv; ++arg; +} + +//:: Helper function used by the above fragment of code (and later layers too, +//:: who knows?). +//: The :(code) directive appends function definitions to the end of the +//: project. Regardless of where functions are defined, we can call them +//: anywhere we like as long as we format the function header in a specific +//: way: put it all on a single line without indent, end the line with ') {' +//: and no trailing whitespace. As long as functions uniformly start this +//: way, our 'build' script contains a little command to automatically +//: generate declarations for them. +:(code) +bool is_equal(char* s, const char* lit) { + return strncmp(s, lit, strlen(lit)) == 0; +} + +bool starts_with(const string& s, const string& pat) { + string::const_iterator a=s.begin(), b=pat.begin(); + for (/*nada*/; a!=s.end() && b!=pat.end(); ++a, ++b) + if (*a != *b) return false; + return b == pat.end(); +} + +//: I'll throw some style conventions here for want of a better place for them. +//: As a rule I hate style guides. Do what you want, that's my motto. But since +//: we're dealing with C/C++, the one big thing we want to avoid is undefined +//: behavior. If a compiler ever encounters undefined behavior it can make +//: your program do anything it wants. +//: +//: For reference, my checklist of undefined behaviors to watch out for: +//: out-of-bounds access +//: uninitialized variables +//: use after free +//: dereferencing invalid pointers: null, a new of size 0, others +//: +//: casting a large number to a type too small to hold it +//: +//: integer overflow +//: division by zero and other undefined expressions +//: left-shift by negative count +//: shifting values by more than or equal to the number of bits they contain +//: bitwise operations on signed numbers +//: +//: Converting pointers to types of different alignment requirements +//: T* -> void* -> T*: defined +//: T* -> U* -> T*: defined if non-function pointers and alignment requirements are same +//: function pointers may be cast to other function pointers +//: +//: Casting a numeric value into a value that can't be represented by the target type (either directly or via static_cast) +//: +//: To guard against these, some conventions: +//: +//: 0. Initialize all primitive variables in functions and constructors. +//: +//: 1. Minimize use of pointers and pointer arithmetic. Avoid 'new' and +//: 'delete' as far as possible. Rely on STL to perform memory management to +//: avoid use-after-free issues (and memory leaks). +//: +//: 2. Avoid naked arrays to avoid out-of-bounds access. Never use operator[] +//: except with map. Use at() with STL vectors and so on. +//: +//: 3. Valgrind all the things. +//: +//: 4. Avoid unsigned numbers. Not strictly an undefined-behavior issue, but +//: the extra range doesn't matter, and it's one less confusing category of +//: interaction gotchas to worry about. +//: +//: Corollary: don't use the size() method on containers, since it returns an +//: unsigned and that'll cause warnings about mixing signed and unsigned, +//: yadda-yadda. Instead use this macro below to perform an unsafe cast to +//: signed. We'll just give up immediately if a container's ever too large. +//: Basically, Mu is not concerned about this being a little slower than it +//: could be. (https://gist.github.com/rygorous/e0f055bfb74e3d5f0af20690759de5a7) +//: +//: Addendum to corollary: We're going to uniformly use int everywhere, to +//: indicate that we're oblivious to number size, and since Clang on 32-bit +//: platforms doesn't yet support multiplication over 64-bit integers, and +//: since multiplying two integers seems like a more common situation to end +//: up in than integer overflow. +:(before "End Includes") +#define SIZE(X) (assert((X).size() < (1LL<<(sizeof(int)*8-2))), static_cast<int>((X).size())) + +//: 5. Integer overflow is guarded against at runtime using the -ftrapv flag +//: to the compiler, supported by Clang (GCC version only works sometimes: +//: http://stackoverflow.com/questions/20851061/how-to-make-gcc-ftrapv-work). +:(before "atexit(teardown)") +initialize_signal_handlers(); // not always necessary, but doesn't hurt +//? cerr << INT_MAX+1 << '\n'; // test overflow +//? assert(false); // test SIGABRT +:(code) +// based on https://spin.atomicobject.com/2013/01/13/exceptions-stack-traces-c +void initialize_signal_handlers() { + struct sigaction action; + bzero(&action, sizeof(action)); + action.sa_sigaction = dump_and_exit; + sigemptyset(&action.sa_mask); + sigaction(SIGABRT, &action, NULL); // assert() failure or integer overflow on linux (with -ftrapv) + sigaction(SIGILL, &action, NULL); // integer overflow on OS X (with -ftrapv) +} +void dump_and_exit(int sig, unused siginfo_t* dummy1, unused void* dummy2) { + switch (sig) { + case SIGABRT: + #ifndef __APPLE__ + cerr << "SIGABRT: might be an integer overflow if it wasn't an assert() failure\n"; + _Exit(1); + #endif + break; + case SIGILL: + #ifdef __APPLE__ + cerr << "SIGILL: most likely caused by integer overflow\n"; + _Exit(1); + #endif + break; + default: + break; + } +} +:(before "End Includes") +#include <signal.h> + +//: For good measure we'll also enable SIGFPE. +:(before "atexit(teardown)") +feenableexcept(FE_OVERFLOW | FE_UNDERFLOW); +//? assert(sizeof(int) == 4 && sizeof(float) == 4); +//? // | exp | mantissa +//? int smallest_subnormal = 0b00000000000000000000000000000001; +//? float smallest_subnormal_f = *reinterpret_cast<float*>(&smallest_subnormal); +//? cerr << "ε: " << smallest_subnormal_f << '\n'; +//? cerr << "ε/2: " << smallest_subnormal_f/2 << " (underflow)\n"; // test SIGFPE +:(before "End Includes") +#include <fenv.h> +:(code) +#ifdef __APPLE__ +// Public domain polyfill for feenableexcept on OS X +// http://www-personal.umich.edu/~williams/archive/computation/fe-handling-example.c +int feenableexcept (unsigned int excepts) { + static fenv_t fenv; + unsigned int new_excepts = excepts & FE_ALL_EXCEPT; + unsigned int old_excepts; + if (fegetenv(&fenv)) return -1; + old_excepts = fenv.__control & FE_ALL_EXCEPT; + fenv.__control &= ~new_excepts; + fenv.__mxcsr &= ~(new_excepts << 7); + return fesetenv(&fenv) ? -1 : old_excepts; +} +#endif + +//: 6. Map's operator[] being non-const is fucking evil. +:(before "Globals") // can't generate prototypes for these +// from http://stackoverflow.com/questions/152643/idiomatic-c-for-reading-from-a-const-map +template<typename T> typename T::mapped_type& get(T& map, typename T::key_type const& key) { + typename T::iterator iter(map.find(key)); + assert(iter != map.end()); + return iter->second; +} +template<typename T> typename T::mapped_type const& get(const T& map, typename T::key_type const& key) { + typename T::const_iterator iter(map.find(key)); + assert(iter != map.end()); + return iter->second; +} +template<typename T> typename T::mapped_type const& put(T& map, typename T::key_type const& key, typename T::mapped_type const& value) { + map[key] = value; + return map[key]; +} +template<typename T> bool contains_key(T& map, typename T::key_type const& key) { + return map.find(key) != map.end(); +} +template<typename T> typename T::mapped_type& get_or_insert(T& map, typename T::key_type const& key) { + return map[key]; +} +//: The contract: any container that relies on get_or_insert should never call +//: contains_key. + +//: 7. istreams are a royal pain in the arse. You have to be careful about +//: what subclass you try to putback into. You have to watch out for the pesky +//: failbit and badbit. Just avoid eof() and use this helper instead. +:(code) +bool has_data(istream& in) { + return in && !in.eof(); +} + +:(before "End Includes") +#include <assert.h> + +#include <iostream> +using std::istream; +using std::ostream; +using std::iostream; +using std::cin; +using std::cout; +using std::cerr; +#include <iomanip> + +#include <string.h> +#include <string> +using std::string; + +#define unused __attribute__((unused)) |