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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))
|