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/*
* Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
using System;
using System.Collections.Generic;
/*
* Execution of code during compilation is done in a virtual CPU
* incarnated by this class, that contains the relevant registers.
*
* Accesses to the data on the stack are mapped to accesses to an
* internal array, with no explicit control on boundaries. Since the
* internal array may be larger than the actual stack contents,
* nonsensical accesses may still "work" to some extent. The whole
* thing won't derail beyond the CLR VM, though.
*/
class CPU {
/*
* Next instruction to execute is in ipBuf[ipOff].
*/
internal Opcode[] ipBuf;
internal int ipOff;
/*
* stackBuf and stackPtr implement the data stack. The system
* stack uses frames; 'rsp' points to the current top frame.
*/
TValue[] stackBuf;
int stackPtr;
Frame rsp;
internal CPU()
{
stackBuf = new TValue[16];
stackPtr = -1;
rsp = null;
}
/*
* Enter a function, reserving space for 'numLocals' local variables.
*/
internal void Enter(Opcode[] code, int numLocals)
{
Frame f = new Frame(rsp, numLocals);
rsp = f;
f.savedIpBuf = ipBuf;
f.savedIpOff = ipOff;
ipBuf = code;
ipOff = 0;
}
/*
* Exit the current function.
*/
internal void Exit()
{
ipBuf = rsp.savedIpBuf;
ipOff = rsp.savedIpOff;
rsp = rsp.upper;
}
/*
* Get the current stack depth (number of elements).
*/
internal int Depth {
get {
return stackPtr + 1;
}
}
/*
* Pop a value from the stack.
*/
internal TValue Pop()
{
return stackBuf[stackPtr --];
}
/*
* Push a value on the stack.
*/
internal void Push(TValue v)
{
int len = stackBuf.Length;
if (++ stackPtr == len) {
TValue[] nbuf = new TValue[len << 1];
Array.Copy(stackBuf, 0, nbuf, 0, len);
stackBuf = nbuf;
}
stackBuf[stackPtr] = v;
}
/*
* Look at the value at depth 'depth' (0 is top of stack). The
* stack is unchanged.
*/
internal TValue Peek(int depth)
{
return stackBuf[stackPtr - depth];
}
/*
* Rotate the stack at depth 'depth': the value at that depth
* is moved to the top of stack.
*/
internal void Rot(int depth)
{
TValue v = stackBuf[stackPtr - depth];
Array.Copy(stackBuf, stackPtr - (depth - 1),
stackBuf, stackPtr - depth, depth);
stackBuf[stackPtr] = v;
}
/*
* Inverse-rotate the stack at depth 'depth': the value at the
* top of stack is moved to that depth.
*/
internal void NRot(int depth)
{
TValue v = stackBuf[stackPtr];
Array.Copy(stackBuf, stackPtr - depth,
stackBuf, stackPtr - (depth - 1), depth);
stackBuf[stackPtr - depth] = v;
}
/*
* Get the current contents of the local variable 'num'.
*/
internal TValue GetLocal(int num)
{
return rsp.locals[num];
}
/*
* Set the contents of the local variable 'num'.
*/
internal void PutLocal(int num, TValue v)
{
rsp.locals[num] = v;
}
/*
* The system stack really is a linked list of Frame instances.
*/
class Frame {
internal Frame upper;
internal Opcode[] savedIpBuf;
internal int savedIpOff;
internal TValue[] locals;
internal Frame(Frame upper, int numLocals)
{
this.upper = upper;
locals = new TValue[numLocals];
}
}
}
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