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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"
static inline uint32_t 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;
}
static offs_t ssem_dasm_one(std::ostream &stream, offs_t pc, uint32_t op)
{
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 | DASMFLAG_SUPPORTED;
}
/*****************************************************************************/
CPU_DISASSEMBLE( ssem )
{
uint32_t op = (*(uint8_t *)(opram + 0) << 24) |
(*(uint8_t *)(opram + 1) << 16) |
(*(uint8_t *)(opram + 2) << 8) |
(*(uint8_t *)(opram + 3) << 0);
return ssem_dasm_one(stream, pc, op);
}
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