_ Git - BearSSL/blob - T0/CPU.cs

   1 /*
   2  * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining
   5  * a copy of this software and associated documentation files (the
   6  * "Software"), to deal in the Software without restriction, including
   7  * without limitation the rights to use, copy, modify, merge, publish,
   8  * distribute, sublicense, and/or sell copies of the Software, and to
   9  * permit persons to whom the Software is furnished to do so, subject to
  10  * the following conditions:
  11  *
  12  * The above copyright notice and this permission notice shall be
  13  * included in all copies or substantial portions of the Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  16  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  17  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  18  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  19  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  20  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  21  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  22  * SOFTWARE.
  23  */
  24
  25 using System;
  26 using System.Collections.Generic;
  27
  28 /*
  29  * Execution of code during compilation is done in a virtual CPU
  30  * incarnated by this class, that contains the relevant registers.
  31  *
  32  * Accesses to the data on the stack are mapped to accesses to an
  33  * internal array, with no explicit control on boundaries. Since the
  34  * internal array may be larger than the actual stack contents,
  35  * nonsensical accesses may still "work" to some extent. The whole
  36  * thing won't derail beyond the CLR VM, though.
  37  */
  38
  39 class CPU {
  40
  41         /*
  42          * Next instruction to execute is in ipBuf[ipOff].
  43          */
  44         internal Opcode[] ipBuf;
  45         internal int ipOff;
  46
  47         /*
  48          * stackBuf and stackPtr implement the data stack. The system
  49          * stack uses frames; 'rsp' points to the current top frame.
  50          */
  51         TValue[] stackBuf;
  52         int stackPtr;
  53         Frame rsp;
  54
  55         internal CPU()
  56         {
  57                 stackBuf = new TValue[16];
  58                 stackPtr = -1;
  59                 rsp = null;
  60         }
  61
  62         /*
  63          * Enter a function, reserving space for 'numLocals' local variables.
  64          */
  65         internal void Enter(Opcode[] code, int numLocals)
  66         {
  67                 Frame f = new Frame(rsp, numLocals);
  68                 rsp = f;
  69                 f.savedIpBuf = ipBuf;
  70                 f.savedIpOff = ipOff;
  71                 ipBuf = code;
  72                 ipOff = 0;
  73         }
  74
  75         /*
  76          * Exit the current function.
  77          */
  78         internal void Exit()
  79         {
  80                 ipBuf = rsp.savedIpBuf;
  81                 ipOff = rsp.savedIpOff;
  82                 rsp = rsp.upper;
  83         }
  84
  85         /*
  86          * Get the current stack depth (number of elements).
  87          */
  88         internal int Depth {
  89                 get {
  90                         return stackPtr + 1;
  91                 }
  92         }
  93
  94         /*
  95          * Pop a value from the stack.
  96          */
  97         internal TValue Pop()
  98         {
  99                 return stackBuf[stackPtr --];
 100         }
 101
 102         /*
 103          * Push a value on the stack.
 104          */
 105         internal void Push(TValue v)
 106         {
 107                 int len = stackBuf.Length;
 108                 if (++ stackPtr == len) {
 109                         TValue[] nbuf = new TValue[len << 1];
 110                         Array.Copy(stackBuf, 0, nbuf, 0, len);
 111                         stackBuf = nbuf;
 112                 }
 113                 stackBuf[stackPtr] = v;
 114         }
 115
 116         /*
 117          * Look at the value at depth 'depth' (0 is top of stack). The
 118          * stack is unchanged.
 119          */
 120         internal TValue Peek(int depth)
 121         {
 122                 return stackBuf[stackPtr - depth];
 123         }
 124
 125         /*
 126          * Rotate the stack at depth 'depth': the value at that depth
 127          * is moved to the top of stack.
 128          */
 129         internal void Rot(int depth)
 130         {
 131                 TValue v = stackBuf[stackPtr - depth];
 132                 Array.Copy(stackBuf, stackPtr - (depth - 1),
 133                         stackBuf, stackPtr - depth, depth);
 134                 stackBuf[stackPtr] = v;
 135         }
 136
 137         /*
 138          * Inverse-rotate the stack at depth 'depth': the value at the
 139          * top of stack is moved to that depth.
 140          */
 141         internal void NRot(int depth)
 142         {
 143                 TValue v = stackBuf[stackPtr];
 144                 Array.Copy(stackBuf, stackPtr - depth,
 145                         stackBuf, stackPtr - (depth - 1), depth);
 146                 stackBuf[stackPtr - depth] = v;
 147         }
 148
 149         /*
 150          * Get the current contents of the local variable 'num'.
 151          */
 152         internal TValue GetLocal(int num)
 153         {
 154                 return rsp.locals[num];
 155         }
 156
 157         /*
 158          * Set the contents of the local variable 'num'.
 159          */
 160         internal void PutLocal(int num, TValue v)
 161         {
 162                 rsp.locals[num] = v;
 163         }
 164
 165         /*
 166          * The system stack really is a linked list of Frame instances.
 167          */
 168         class Frame {
 169
 170                 internal Frame upper;
 171                 internal Opcode[] savedIpBuf;
 172                 internal int savedIpOff;
 173                 internal TValue[] locals;
 174
 175                 internal Frame(Frame upper, int numLocals)
 176                 {
 177                         this.upper = upper;
 178                         locals = new TValue[numLocals];
 179                 }
 180         }
 181 }