gotch/libtch

NOTES ON WRITING WRAPPER FUNCTIONS

Function Input Arguments

tensor -> t *C_tensor

void at_print(tensor);

func AtPrint(t *C_tensor) {
	c_tensor := (C.tensor)((*t).private)
	C.at_print(c_tensor)
}

C pointer e.g int64_t * -> ptr unsafe.Pointer

In function body, cPtr := (*C.long)(ptr)

void at_shape(tensor, int64_t *);

func AtShape(t *C_tensor, ptr unsafe.Pointer) {
	c_tensor := (C.tensor)((*t).private)
	c_ptr := (*C.long)(ptr)
	C.at_shape(c_tensor, c_ptr)
}

C types e.g size_t ndims -> equivalent Go types ndims uint

In function body, c_ndims := *(*C.size_t)(unsafe.Pointer(&ndims))

tensor at_tensor_of_data(void *vs, int64_t *dims, size_t ndims, size_t element_size_in_bytes, int type);

func AtTensorOfData(vs unsafe.Pointer, dims []int64, ndims uint, elt_size_in_bytes uint, kind int) *C_tensor {

    // 1. Unsafe pointer
	c_dims := (*C.int64_t)(unsafe.Pointer(&dims[0]))
	c_ndims := *(*C.size_t)(unsafe.Pointer(&ndims))
	c_elt_size_in_bytes := *(*C.size_t)(unsafe.Pointer(&elt_size_in_bytes))
	c_kind := *(*C.int)(unsafe.Pointer(&kind))

    // 2. Call C function
	t := C.at_tensor_of_data(vs, c_dims, c_ndims, c_elt_size_in_bytes, c_kind)

    // 3. Form return value
	return &C_tensor{private: unsafe.Pointer(t)}
}

Function Return

void *

void *at_data_ptr(tensor);

func AtDataPtr(t *C_tensor) unsafe.Pointer {
	c_tensor := (C.tensor)((*t).private)
	return C.at_data_ptr(c_tensor)
}

tensor -> *C_tensor

then in the return of function body

    // Call C function
    t := C.FUNCTION_TO_CALL(...)
    // Return
	return &C_tensor{private: unsafe.Pointer(t)}

C types e.g. C_ulong -> Go equivalent types uint64

then in the return of function body

	c_result := C.FUNCTION_CALL(...)
	return *(*uint64)(unsafe.Pointer(&c_result))

C type pointers e.g. char *FUNCTION() --> *C.char

then just return the C function call.

char *get_and_reset_last_err(); // thread-local

func GetAndResetLastErr() *C.char{
   return C.get_and_reset_last_err()
}