static PHYSFS_sint64
RGSS_ioRead(PHYSFS_Io *self, void *buffer, PHYSFS_uint64 len)
{
RGSS_entryHandle *entry = static_cast<RGSS_entryHandle*>(self->opaque);
PHYSFS_Io *io = entry->io;
uint64_t toRead = std::min<uint64_t>(entry->data.size - entry->currentOffset, len);
uint64_t offs = entry->currentOffset;
io->seek(io, entry->data.offset + offs);
/* We divide up the bytes to be read in 3 categories:
*
* preAlign: If the current read address is not dword
* aligned, this is the number of bytes to read til
* we reach alignment again (therefore can only be
* 3 or less).
*
* align: The number of aligned dwords we can read
* times 4 (= number of bytes).
*
* postAlign: The number of bytes to read after the
* last aligned dword. Always 3 or less.
*
* Treating the pre- and post aligned reads specially,
* we can read all aligned dwords in one syscall directly
* into the write buffer and then run the xor chain on
* it afterwards. */
uint8_t preAlign = 4 - (offs % 4);
if (preAlign == 4)
preAlign = 0;
else
preAlign = std::min<uint64_t>(preAlign, len);
uint8_t postAlign = (len > preAlign) ? (offs + len) % 4 : 0;
uint64_t align = len - (preAlign + postAlign);
/* Byte buffer pointer */
uint8_t *bBufferP = static_cast<uint8_t*>(buffer);
if (preAlign > 0)
{
uint32_t dword;
io->read(io, &dword, preAlign);
/* Need to align the bytes with the
* magic before xoring */
dword <<= 8 * (offs % 4);
dword ^= entry->currentMagic;
/* Shift them back to normal */
dword >>= 8 * (offs % 4);
memcpy(bBufferP, &dword, preAlign);
bBufferP += preAlign;
/* Only advance the magic if we actually
* reached the next alignment */
if ((offs+preAlign) % 4 == 0)
advanceMagic(entry->currentMagic);
}
