1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
|
#include "alu.h"
#include "qtmipsexception.h"
using namespace machine;
std::uint32_t machine::alu_operate(enum AluOp operation, std::uint32_t s, std::uint32_t t, std::uint8_t sa, Registers *regs) {
switch(operation) {
case ALU_OP_SLL:
return t << sa;
case ALU_OP_SRL:
return t >> sa;
case ALU_OP_SRA:
// TODO is this correct implementation? (Should we be masking top most bit?)
return ((t & 0x7fffffff) >> sa) | (t & 0x80000000);
case ALU_OP_SLLV:
return t << s;
case ALU_OP_SRLV:
return t >> s;
case ALU_OP_SRAV:
// TODO is this correct implementation? (Should we be masking top most bit?)
return ((t & 0x7fffffff) >> s) | (t & 0x80000000);
case ALU_OP_JR:
case ALU_OP_JALR:
// Do nothing as we solve this when we are handling program counter in instruction decode (handle_pc)
return 0;
case ALU_OP_MOVZ:
// We do this just to implement valid alu operation but we have to evaluate comparison way before this to disable register write
return t == 0 ? s : 0;
case ALU_OP_MOVN:
// Same note as for MOVZ applies here
return t != 0 ? s : 0;
case ALU_OP_MFHI:
return regs->read_hi_lo(true);
case ALU_OP_MTHI:
regs->write_hi_lo(true, s);
return 0x0;
case ALU_OP_MFLO:
return regs->read_hi_lo(false);
case ALU_OP_MTLO:
regs->write_hi_lo(false, s);
return 0x0;
case ALU_OP_ADD:
if (s > (0xFFFFFFFF - t))
throw QTMIPS_EXCEPTION(Overflow, "ADD operation overflow/underflow", QString::number(s) + QString(" + ") + QString::number(t));
// Intentional falltrough
case ALU_OP_ADDU:
return s + t;
case ALU_OP_SUB:
if (s < t)
throw QTMIPS_EXCEPTION(Overflow, "SUB operation overflow/underflow", QString::number(s) + QString(" - ") + QString::number(t));
// Intentional falltrough
case ALU_OP_SUBU:
return s - t;
case ALU_OP_AND:
return s & t;
case ALU_OP_OR:
return s | t;
case ALU_OP_XOR:
return s ^ t;
case ALU_OP_NOR:
return ~(s | t);
case ALU_OP_SLT:
// Note: this is in two's complement so there is difference in unsigned and signed compare
return ((std::int32_t)s < (std::int32_t)t) ? 1 : 0;
case ALU_OP_SLTU:
return (s < t) ? 1 : 0;
default:
throw QTMIPS_EXCEPTION(UnsupportedAluOperation, "Unknown ALU operation", QString::number(operation, 16));
}
}
|
