Nim - This repository contains the Nim compiler, Nim's stdlib, tools, and documentation. (mirror)

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//: 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 || is_equal(argv[1], "--help")) { //: this is the functionality later layers will provide // currently no automated tests for commandline arg parsing cerr << "Usage:\n" << " subx test\n"; return 0; } //:: 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(reset)") 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(reset)") 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))


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