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#include "alu.h"
#include "qtmipsexception.h"
#include "utils.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) {
std::int64_t s64_val;
std::uint64_t u64_val;
switch(operation) {
case ALU_OP_SLL:
return t << sa;
case ALU_OP_SRL:
return t >> sa;
case ALU_OP_SRA:
// Note: This might be broken with some compilers but works with gcc
return (std::int32_t)t >> sa;
case ALU_OP_SLLV:
return t << s;
case ALU_OP_SRLV:
return t >> s;
case ALU_OP_SRAV:
// Note: same note as in case of SRA
return (std::int32_t)t >> s;
case ALU_OP_JR:
// Do nothing as we solve this when we are handling program counter in instruction decode (handle_pc)
return 0;
case ALU_OP_JALR:
// Pass return value in rt to save PC after isntruction, program counter is handled in handle_pc
return t;
case ALU_OP_MOVZ:
// We do this just to implement valid alu operation but we have to evaluate comparison outside of this function 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_BREAK:
return 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_MULT:
s64_val = (std::int64_t)(std::int32_t)s * (std::int32_t)t;
regs->write_hi_lo(false, (std::uint32_t)(s64_val & 0xffffffff));
regs->write_hi_lo(true, (std::uint32_t)(s64_val >> 32));
return 0x0;
case ALU_OP_MULTU:
u64_val = (std::uint64_t)s * t;
regs->write_hi_lo(false, (std::uint32_t)(u64_val & 0xffffffff));
regs->write_hi_lo(true, (std::uint32_t)(u64_val >> 32));
return 0x0;
case ALU_OP_DIV:
regs->write_hi_lo(false, (std::uint32_t)((std::int32_t)s / (std::int32_t)t));
regs->write_hi_lo(true, (std::uint32_t)((std::int32_t)s % (std::int32_t)t));
return 0x0;
case ALU_OP_DIVU:
regs->write_hi_lo(false, s / t);
regs->write_hi_lo(true, s % t);
return 0x0;
case ALU_OP_ADD:
/* s(31) ^ ~t(31) ... same signs on input */
/* (s + t)(31) ^ s(31) ... different sign on output */
if (((s ^ ~t) & ((s + t) ^ s)) & 0x80000000)
throw QTMIPS_EXCEPTION(Overflow, "ADD operation overflow/underflow", QString::number(s) + QString(" + ") + QString::number(t));
FALLTROUGH
case ALU_OP_ADDU:
return s + t;
case ALU_OP_SUB:
/* s(31) ^ t(31) ... differnt signd on input */
/* (s - t)(31) ^ ~s(31) <> 0 ... otput sign differs from s */
if (((s ^ t) & ((s - t) ^ s)) & 0x80000000)
throw QTMIPS_EXCEPTION(Overflow, "SUB operation overflow/underflow", QString::number(s) + QString(" - ") + QString::number(t));
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;
case ALU_OP_LUI:
return t << 16;
case ALU_OP_PASS_S: // Pass s argument without change for JAL
return s;
default:
throw QTMIPS_EXCEPTION(UnsupportedAluOperation, "Unknown ALU operation", QString::number(operation, 16));
}
}
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