Embedding C

Embedding C

Since C is the intermediate language used when generating machine code, we can allow a subset of C as an embedded high performance language.

It does not need to be full blown C as that would be too risky. Instead the goal should be to allow C to write snippets of high performance code.

Following features will not be provided:

• Preprocessor
• Ability to call functions or allocate memory
• The interaction between Ravi and C will be limited to userdata types and primitive types / primitive arrays and strings. No access to Lua tables.
• No assignments to Ravi primitive types in C code (this may be added as a feature later on)

Proposed syntax

A new keyword C will be added. It will take a list of symbols and a string argument.

C [[
   typedef struct {
      int i;
  } MyStruct;
]]

local i: integer = 1
local j: integer = 2

C(i,j) [[
     long long k = i+j; // Okay as primitive types
]]

When accessing userdata, string or primitive integer types, following implicit types will be used:

// For userdata and string types
typedef struct {
   char *ptr;
   size_t len;
} Ravi_StringOrUserData;

// For integer[]
typedef struct {
  lua_Integer *data;
  unsigned int length;
} Ravi_IntegerArray;

// For number[]  
typedef struct {
  lua_Number *data;
  unsigned int length;
} Ravi_NumberArray;

Userdata, string or primitive arrays declared in Ravi code will be accessed in the C snippet as follows:

local narray: number[] = table.numarray(100)
local udata: SomeType = getudata()

C(udata, narray) [[
   Ravi_NumberArray *numarray = narray;
   Ravi_StringOrUserData *udataptr = udata;
   // C code can cast the udataptr->ptr to appropriate type
   MyStruct *mystruct = (MyStruct *)udataptr->ptr;
   // do something with mystruct
]]