scripted-engine/src/logic/wren/vm/wren_common.h

#ifndef wren_common_h
#define wren_common_h

// This header contains macros and defines used across the entire Wren
// implementation. In particular, it contains "configuration" defines that
// control how Wren works. Some of these are only used while hacking on Wren
// itself.
//
// This header is *not* intended to be included by code outside of Wren itself.

// Wren pervasively uses the C99 integer types (uint16_t, etc.) along with some
// of the associated limit constants (UINT32_MAX, etc.). The constants are not
// part of standard C++, so aren't included by default by C++ compilers when you
// include <stdint> unless __STDC_LIMIT_MACROS is defined.
#define __STDC_LIMIT_MACROS
#include <stdint.h>

// These flags let you control some details of the interpreter's implementation.
// Usually they trade-off a bit of portability for speed. They default to the
// most efficient behavior.

// If true, then Wren uses a NaN-tagged double for its core value
// representation. Otherwise, it uses a larger more conventional struct. The
// former is significantly faster and more compact. The latter is useful for
// debugging and may be more portable.
//
// Defaults to on.
#ifndef WREN_NAN_TAGGING
  #define WREN_NAN_TAGGING 1
#endif

// If true, the VM's interpreter loop uses computed gotos. See this for more:
// http://gcc.gnu.org/onlinedocs/gcc-3.1.1/gcc/Labels-as-Values.html
// Enabling this speeds up the main dispatch loop a bit, but requires compiler
// support.
//
// Defaults to true on supported compilers.
#ifndef WREN_COMPUTED_GOTO
  #ifdef _MSC_VER
    // No computed gotos in Visual Studio.
    #define WREN_COMPUTED_GOTO 0
  #else
    #define WREN_COMPUTED_GOTO 1
  #endif
#endif

// The VM includes a number of optional modules. You can choose to include
// these or not. By default, they are all available. To disable one, set the
// corresponding `WREN_OPT_<name>` define to `0`.
#ifndef WREN_OPT_META
  #define WREN_OPT_META 1
#endif

#ifndef WREN_OPT_RANDOM
  #define WREN_OPT_RANDOM 1
#endif

// These flags are useful for debugging and hacking on Wren itself. They are not
// intended to be used for production code. They default to off.

// Set this to true to stress test the GC. It will perform a collection before
// every allocation. This is useful to ensure that memory is always correctly
// reachable.
#define WREN_DEBUG_GC_STRESS 0

// Set this to true to log memory operations as they occur.
#define WREN_DEBUG_TRACE_MEMORY 0

// Set this to true to log garbage collections as they occur.
#define WREN_DEBUG_TRACE_GC 0

// Set this to true to print out the compiled bytecode of each function.
#define WREN_DEBUG_DUMP_COMPILED_CODE 0

// Set this to trace each instruction as it's executed.
#define WREN_DEBUG_TRACE_INSTRUCTIONS 0

// The maximum number of module-level variables that may be defined at one time.
// This limitation comes from the 16 bits used for the arguments to
// `CODE_LOAD_MODULE_VAR` and `CODE_STORE_MODULE_VAR`.
#define MAX_MODULE_VARS 65536

// The maximum number of arguments that can be passed to a method. Note that
// this limitation is hardcoded in other places in the VM, in particular, the
// `CODE_CALL_XX` instructions assume a certain maximum number.
#define MAX_PARAMETERS 16

// The maximum name of a method, not including the signature. This is an
// arbitrary but enforced maximum just so we know how long the method name
// strings need to be in the parser.
#define MAX_METHOD_NAME 64

// The maximum length of a method signature. Signatures look like:
//
//     foo        // Getter.
//     foo()      // No-argument method.
//     foo(_)     // One-argument method.
//     foo(_,_)   // Two-argument method.
//     init foo() // Constructor initializer.
//
// The maximum signature length takes into account the longest method name, the
// maximum number of parameters with separators between them, "init ", and "()".
#define MAX_METHOD_SIGNATURE (MAX_METHOD_NAME + (MAX_PARAMETERS * 2) + 6)

// The maximum length of an identifier. The only real reason for this limitation
// is so that error messages mentioning variables can be stack allocated.
#define MAX_VARIABLE_NAME 64

// The maximum number of fields a class can have, including inherited fields.
// This is explicit in the bytecode since `CODE_CLASS` and `CODE_SUBCLASS` take
// a single byte for the number of fields. Note that it's 255 and not 256
// because creating a class takes the *number* of fields, not the *highest
// field index*.
#define MAX_FIELDS 255

// Use the VM's allocator to allocate an object of [type].
#define ALLOCATE(vm, type) \
    ((type*)wrenReallocate(vm, NULL, 0, sizeof(type)))

// Use the VM's allocator to allocate an object of [mainType] containing a
// flexible array of [count] objects of [arrayType].
#define ALLOCATE_FLEX(vm, mainType, arrayType, count) \
    ((mainType*)wrenReallocate(vm, NULL, 0, \
    sizeof(mainType) + sizeof(arrayType) * (count)))

// Use the VM's allocator to allocate an array of [count] elements of [type].
#define ALLOCATE_ARRAY(vm, type, count) \
    ((type*)wrenReallocate(vm, NULL, 0, sizeof(type) * (count)))

// Use the VM's allocator to free the previously allocated memory at [pointer].
#define DEALLOCATE(vm, pointer) wrenReallocate(vm, pointer, 0, 0)

// The Microsoft compiler does not support the "inline" modifier when compiling
// as plain C.
#if defined( _MSC_VER ) && !defined(__cplusplus)
  #define inline _inline
#endif

// This is used to clearly mark flexible-sized arrays that appear at the end of
// some dynamically-allocated structs, known as the "struct hack".
#if __STDC_VERSION__ >= 199901L
  // In C99, a flexible array member is just "[]".
  #define FLEXIBLE_ARRAY
#else
  // Elsewhere, use a zero-sized array. It's technically undefined behavior,
  // but works reliably in most known compilers.
  #define FLEXIBLE_ARRAY 0
#endif

// Assertions are used to validate program invariants. They indicate things the
// program expects to be true about its internal state during execution. If an
// assertion fails, there is a bug in Wren.
//
// Assertions add significant overhead, so are only enabled in debug builds.
#ifdef DEBUG

  #include <stdio.h>

  #define ASSERT(condition, message) \
      do \
      { \
        if (!(condition)) \
        { \
          fprintf(stderr, "[%s:%d] Assert failed in %s(): %s\n", \
              __FILE__, __LINE__, __func__, message); \
          abort(); \
        } \
      } \
      while(0)

  // Indicates that we know execution should never reach this point in the
  // program. In debug mode, we assert this fact because it's a bug to get here.
  //
  // In release mode, we use compiler-specific built in functions to tell the
  // compiler the code can't be reached. This avoids "missing return" warnings
  // in some cases and also lets it perform some optimizations by assuming the
  // code is never reached.
  #define UNREACHABLE() \
      do \
      { \
        fprintf(stderr, "[%s:%d] This code should not be reached in %s()\n", \
            __FILE__, __LINE__, __func__); \
        abort(); \
      } \
      while (0)

#else

  #define ASSERT(condition, message) do {} while (0)

  // Tell the compiler that this part of the code will never be reached.
  #if defined( _MSC_VER )
    #define UNREACHABLE() __assume(0)
  #elif (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 5))
    #define UNREACHABLE() __builtin_unreachable()
  #else
    #define UNREACHABLE()
  #endif

#endif

#endif