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// license:BSD-3-Clause
// copyright-holders:Ryan Holtz
/*
Manchester Small-Scale Experimental Machine (SSEM) disassembler
Written by Ryan Holtz
*/
#include "emu.h"
#include "ssemdasm.h"
inline uint32_t ssem_disassembler::reverse(uint32_t v)
{
// Taken from http://www-graphics.stanford.edu/~seander/bithacks.html#ReverseParallel
// swap odd and even bits
v = ((v >> 1) & 0x55555555) | ((v & 0x55555555) << 1);
// swap consecutive pairs
v = ((v >> 2) & 0x33333333) | ((v & 0x33333333) << 2);
// swap nibbles ...
v = ((v >> 4) & 0x0F0F0F0F) | ((v & 0x0F0F0F0F) << 4);
// swap bytes
v = ((v >> 8) & 0x00FF00FF) | ((v & 0x00FF00FF) << 8);
// swap 2-byte long pairs
v = ( v >> 16 ) | ( v << 16);
return v;
}
u32 ssem_disassembler::opcode_alignment() const
{
return 4;
}
offs_t ssem_disassembler::disassemble(std::ostream &stream, offs_t pc, const data_buffer &opcodes, const data_buffer ¶ms)
{
uint32_t op = opcodes.r32(pc);
uint8_t instr = (reverse(op) >> 13) & 7;
uint8_t addr = reverse(op) & 0x1f;
switch (instr)
{
case 0: // JMP S
util::stream_format(stream, "JMP %d", addr);
break;
case 1: // JRP S
util::stream_format(stream, "JRP %d", addr);
break;
case 2: // LDN S
util::stream_format(stream, "LDN %d", addr);
break;
case 3: // STO S
util::stream_format(stream, "STO %d", addr);
break;
case 4: // SUB S
case 5:
util::stream_format(stream, "SUB %d", addr);
break;
case 6: // CMP
util::stream_format(stream, "CMP");
break;
case 7: // STP
util::stream_format(stream, "STP");
break;
default:
util::stream_format(stream, "???");
break;
}
return 4 | (instr == 6 ? STEP_COND : 0) | SUPPORTED;
}
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