static int MOD_EXP_CTIME_COPY_FROM_PREBUF(BIGNUM *b, int top, unsigned char *buf, int idx, int width)
	{
	size_t i, j;

	if (bn_wexpand(b, top) == NULL)
		return 0;

	for (i=0, j=idx; i < top * sizeof b->d[0]; i++, j+=width)
		{
		((unsigned char*)b->d)[i] = buf[j];
		}

	b->top = top;
	bn_correct_top(b);
	return 1;
	}