static void ecryptfs_encode_for_filename(unsigned char *dst, size_t *dst_size,
				  unsigned char *src, size_t src_size)
{
	size_t num_blocks;
	size_t block_num = 0;
	size_t dst_offset = 0;
	unsigned char last_block[3];

	if (src_size == 0) {
		(*dst_size) = 0;
		goto out;
	}
	num_blocks = (src_size / 3);
	if ((src_size % 3) == 0) {
		memcpy(last_block, (&src[src_size - 3]), 3);
	} else {
		num_blocks++;
		last_block[2] = 0x00;
		switch (src_size % 3) {
		case 1:
			last_block[0] = src[src_size - 1];
			last_block[1] = 0x00;
			break;
		case 2:
			last_block[0] = src[src_size - 2];
			last_block[1] = src[src_size - 1];
		}
	}
	(*dst_size) = (num_blocks * 4);
	if (!dst)
		goto out;
	while (block_num < num_blocks) {
		unsigned char *src_block;
		unsigned char dst_block[4];

		if (block_num == (num_blocks - 1))
			src_block = last_block;
		else
			src_block = &src[block_num * 3];
		dst_block[0] = ((src_block[0] >> 2) & 0x3F);
		dst_block[1] = (((src_block[0] << 4) & 0x30)
				| ((src_block[1] >> 4) & 0x0F));
		dst_block[2] = (((src_block[1] << 2) & 0x3C)
				| ((src_block[2] >> 6) & 0x03));
		dst_block[3] = (src_block[2] & 0x3F);
		dst[dst_offset++] = portable_filename_chars[dst_block[0]];
		dst[dst_offset++] = portable_filename_chars[dst_block[1]];
		dst[dst_offset++] = portable_filename_chars[dst_block[2]];
		dst[dst_offset++] = portable_filename_chars[dst_block[3]];
		block_num++;
	}
out:
	return;
}

This weakness involves numeric computation errors, such as integer overflows, underflows, or precision losses, which can lead to miscalculations and exploitable behaviors in software.