/**
 * Includes
 */

#define  PY_SSIZE_T_CLEAN  /* So we get Py_ssize_t args. */
#include <Python.h>        /* Because of "reasons", the Python header must be first. */
#include <stdint.h>



/* Extern "C" Guard */
#ifdef __cplusplus
extern "C" {
#endif



/**
 * Data Structure and Constant Definitions
 */

static const uint32_t CRC32CLUT[256] = {
	0x00000000, 0xf26b8303, 0xe13b70f7, 0x1350f3f4, 0xc79a971f, 0x35f1141c, 0x26a1e7e8, 0xd4ca64eb,
	0x8ad958cf, 0x78b2dbcc, 0x6be22838, 0x9989ab3b, 0x4d43cfd0, 0xbf284cd3, 0xac78bf27, 0x5e133c24,
	0x105ec76f, 0xe235446c, 0xf165b798, 0x030e349b, 0xd7c45070, 0x25afd373, 0x36ff2087, 0xc494a384,
	0x9a879fa0, 0x68ec1ca3, 0x7bbcef57, 0x89d76c54, 0x5d1d08bf, 0xaf768bbc, 0xbc267848, 0x4e4dfb4b,
	0x20bd8ede, 0xd2d60ddd, 0xc186fe29, 0x33ed7d2a, 0xe72719c1, 0x154c9ac2, 0x061c6936, 0xf477ea35,
	0xaa64d611, 0x580f5512, 0x4b5fa6e6, 0xb93425e5, 0x6dfe410e, 0x9f95c20d, 0x8cc531f9, 0x7eaeb2fa,
	0x30e349b1, 0xc288cab2, 0xd1d83946, 0x23b3ba45, 0xf779deae, 0x05125dad, 0x1642ae59, 0xe4292d5a,
	0xba3a117e, 0x4851927d, 0x5b016189, 0xa96ae28a, 0x7da08661, 0x8fcb0562, 0x9c9bf696, 0x6ef07595,
	0x417b1dbc, 0xb3109ebf, 0xa0406d4b, 0x522bee48, 0x86e18aa3, 0x748a09a0, 0x67dafa54, 0x95b17957,
	0xcba24573, 0x39c9c670, 0x2a993584, 0xd8f2b687, 0x0c38d26c, 0xfe53516f, 0xed03a29b, 0x1f682198,
	0x5125dad3, 0xa34e59d0, 0xb01eaa24, 0x42752927, 0x96bf4dcc, 0x64d4cecf, 0x77843d3b, 0x85efbe38,
	0xdbfc821c, 0x2997011f, 0x3ac7f2eb, 0xc8ac71e8, 0x1c661503, 0xee0d9600, 0xfd5d65f4, 0x0f36e6f7,
	0x61c69362, 0x93ad1061, 0x80fde395, 0x72966096, 0xa65c047d, 0x5437877e, 0x4767748a, 0xb50cf789,
	0xeb1fcbad, 0x197448ae, 0x0a24bb5a, 0xf84f3859, 0x2c855cb2, 0xdeeedfb1, 0xcdbe2c45, 0x3fd5af46,
	0x7198540d, 0x83f3d70e, 0x90a324fa, 0x62c8a7f9, 0xb602c312, 0x44694011, 0x5739b3e5, 0xa55230e6,
	0xfb410cc2, 0x092a8fc1, 0x1a7a7c35, 0xe811ff36, 0x3cdb9bdd, 0xceb018de, 0xdde0eb2a, 0x2f8b6829,
	0x82f63b78, 0x709db87b, 0x63cd4b8f, 0x91a6c88c, 0x456cac67, 0xb7072f64, 0xa457dc90, 0x563c5f93,
	0x082f63b7, 0xfa44e0b4, 0xe9141340, 0x1b7f9043, 0xcfb5f4a8, 0x3dde77ab, 0x2e8e845f, 0xdce5075c,
	0x92a8fc17, 0x60c37f14, 0x73938ce0, 0x81f80fe3, 0x55326b08, 0xa759e80b, 0xb4091bff, 0x466298fc,
	0x1871a4d8, 0xea1a27db, 0xf94ad42f, 0x0b21572c, 0xdfeb33c7, 0x2d80b0c4, 0x3ed04330, 0xccbbc033,
	0xa24bb5a6, 0x502036a5, 0x4370c551, 0xb11b4652, 0x65d122b9, 0x97baa1ba, 0x84ea524e, 0x7681d14d,
	0x2892ed69, 0xdaf96e6a, 0xc9a99d9e, 0x3bc21e9d, 0xef087a76, 0x1d63f975, 0x0e330a81, 0xfc588982,
	0xb21572c9, 0x407ef1ca, 0x532e023e, 0xa145813d, 0x758fe5d6, 0x87e466d5, 0x94b49521, 0x66df1622,
	0x38cc2a06, 0xcaa7a905, 0xd9f75af1, 0x2b9cd9f2, 0xff56bd19, 0x0d3d3e1a, 0x1e6dcdee, 0xec064eed,
	0xc38d26c4, 0x31e6a5c7, 0x22b65633, 0xd0ddd530, 0x0417b1db, 0xf67c32d8, 0xe52cc12c, 0x1747422f,
	0x49547e0b, 0xbb3ffd08, 0xa86f0efc, 0x5a048dff, 0x8ecee914, 0x7ca56a17, 0x6ff599e3, 0x9d9e1ae0,
	0xd3d3e1ab, 0x21b862a8, 0x32e8915c, 0xc083125f, 0x144976b4, 0xe622f5b7, 0xf5720643, 0x07198540,
	0x590ab964, 0xab613a67, 0xb831c993, 0x4a5a4a90, 0x9e902e7b, 0x6cfbad78, 0x7fab5e8c, 0x8dc0dd8f,
	0xe330a81a, 0x115b2b19, 0x020bd8ed, 0xf0605bee, 0x24aa3f05, 0xd6c1bc06, 0xc5914ff2, 0x37faccf1,
	0x69e9f0d5, 0x9b8273d6, 0x88d28022, 0x7ab90321, 0xae7367ca, 0x5c18e4c9, 0x4f48173d, 0xbd23943e,
	0xf36e6f75, 0x0105ec76, 0x12551f82, 0xe03e9c81, 0x34f4f86a, 0xc69f7b69, 0xd5cf889d, 0x27a40b9e,
	0x79b737ba, 0x8bdcb4b9, 0x988c474d, 0x6ae7c44e, 0xbe2da0a5, 0x4c4623a6, 0x5f16d052, 0xad7d5351,
};



/* C Function Forward Declarations */
uint32_t  doCRC32C(uint32_t    crc,
                   const char* buf,
                   Py_ssize_t  len);



/* Python Method Forward Declarations */
PyObject* crc32c_update(PyObject* self, PyObject* args);



/* C Function Definitions */

/**
 * The actual CRC32C implementation.
 */

uint32_t  doCRC32C(uint32_t    crc,
                   const char* buf,
                   Py_ssize_t  len){
	Py_ssize_t i;
	
	if(!buf || len<=0){
		return crc;
	}
	
	for(i=0;i<len;i++){
		crc = (crc >> 8) ^ CRC32CLUT[(crc^buf[i]) & 0xFFU];
	}
	
	return crc;
}



/* Python Method Definitions */

/**
 * A wrapper around doCRC32C() that translates from Python objects to C
 * datatypes and vice-versa.
 */

PyObject* crc32c_update(PyObject* self, PyObject* args){
	PyObject*          ret;
	unsigned long      crc32c;
	unsigned long      arg_crc32c = -1;
	const char*        arg_bufptr = NULL;
	Py_ssize_t         arg_buflen = -1;
	unsigned long long arg_len    = -1;
	unsigned long long arg_off    =  0;
	
	
	if(!PyArg_ParseTuple(args, "|kz#KK",
	                     &arg_crc32c,
	                     &arg_bufptr, &arg_buflen,
	                     &arg_len,
	                     &arg_off)){
		PyErr_SetString(PyExc_RuntimeError, "Failed to parse arguments!");
		return NULL;
	}
	if      (arg_len != -1 && arg_off+arg_len > arg_buflen){
		PyErr_SetString(PyExc_ValueError,   "Buffer overflow (offset + length beyond end of buffer)!");
		return NULL;
	}else if(arg_len == -1 && arg_off > arg_buflen){
		PyErr_SetString(PyExc_ValueError,   "Buffer overflow (offset greater than buffer length)!");
		return NULL;
	}else if(arg_len == -1){
		arg_len = arg_buflen-arg_off;
	}
	
	crc32c = doCRC32C(arg_crc32c,
	                  arg_bufptr+arg_off,
	                  arg_len);
	ret = PyLong_FromLong(crc32c);
	
	if(!ret){
		PyErr_SetString(PyExc_RuntimeError, "Failed to allocate Python int!");
	}
	return ret;
}



/**
 * Python Module Definition
 * 
 * Includes:
 *   - Module Documentation
 *   - Module Methods Table
 *   - Module Definition
 *   - Module Initialization Function
 */

static const char  CRC_NATIVE_MODULE_DOC[] = "Native CRC32C Implementation.";

static PyMethodDef crc_native_methods[] = {
	{"crc32c_update", (PyCFunction)crc32c_update, 1,
	 "CRC32C (Castagnoli) update function. Signature: crc32c_update(crc32c=-1, buffer=None, len=-1, offset=0)"},
};

static PyModuleDef crc_native_module_def = {
	PyModuleDef_HEAD_INIT,
	"crc_native",          /* m_name */
	CRC_NATIVE_MODULE_DOC, /* m_doc */
	-1,                    /* m_size */
	crc_native_methods,    /* m_methods */
	NULL,                  /* m_reload */
	NULL,                  /* m_traverse */
	NULL,                  /* m_clear */
	NULL,                  /* m_free */
};

PyMODINIT_FUNC PyInit_crc_native(void){
	PyObject* m = PyModule_Create(&crc_native_module_def);
	if(!m){
		return NULL;
	}else{
		return m;
	}
}


/* End Extern "C" Guard */
#ifdef __cplusplus
}
#endif

