问题
Right now, I'm learning how to interface SICStus Prolog with C code.
I would like to have/use/see a C implementation of "Hamming weight" of arbitrary-sized integers in SICStus Prolog version 4.
It seems to me that I need C functions for testing term types (SP_is_integer) and C functions for accessing Prolog terms (SP_get_integer, SP_get_integer_bytes).
However, I'm not sure how to use SP_get_integer_bytes in a portable, robust fashion. Could you please point me to some well-crafted solid C code doing just that?
回答1:
Use it something like this:
SP_term_ref tr = ... some term ...
int native = 0; // want portable, little endian
size_t buf_size = 0;
if (!SP_get_integer_bytes(tr, NULL, &buf_size, native)
// if buf_size was updated, then there was not really an error
&& buf_size == 0)
{
// Something wrong (e.g., not an integer)
return ERROR;
}
// here buf_size > 0
void *buffer = SP_malloc(buf_size);
if (buffer == NULL)
{
return ERROR;
}
if (!SP_get_integer_bytes(tr, buffer, &buf_size, native))
{
// Something wrong. This would be surprising here
error();
}
// Here buffer contains buf_size bytes, in
// twos-complement, with the least significant bytes at lowest index.
// ... do something with buffer ...
// finally clean up
SP_free(buffer);
来源:https://stackoverflow.com/questions/28832027/passing-arbitrary-sized-integers-from-prolog-to-c