Descrambler.md

EXI Descrambler.

// bootrom descrambler reversed by segher
// Copyright 2008 Segher Boessenkool <segher@kernel.crashing.org>
void Descrambler(u8* data, u32 size)
{
	u8 acc = 0;
	u8 nacc = 0;

	u16 t = 0x2953;
	u16 u = 0xd9c2;
	u16 v = 0x3ff1;

	u8 x = 1;

	for (u32 it = 0; it < size;)
	{
		int t0 = t & 1;
		int t1 = (t >> 1) & 1;
		int u0 = u & 1;
		int u1 = (u >> 1) & 1;
		int v0 = v & 1;

		x ^= t1 ^ v0;
		x ^= (u0 | u1);
		x ^= (t0 ^ u1 ^ v0) & (t0 ^ u0);

		if (t0 == u0)
		{
			v >>= 1;
			if (v0)
				v ^= 0xb3d0;
		}

		if (t0 == 0)
		{
			u >>= 1;
			if (u0)
				u ^= 0xfb10;
		}

		t >>= 1;
		if (t0)
			t ^= 0xa740;

		nacc++;
		acc = 2*acc + x;
		if (nacc == 8)
		{
			data[it++] ^= acc;
			nacc = 0;
		}
	}
}

segher is supercomputer +1