Minsk: emulate shifts, try to emulate R1/R2/ACC faithfully

diff --git a/minsk.c b/minsk.c
index 08e2665600ce1294fd0949f1272c9a69d65abfa1..187aea531ba46e4167f34453f93466c081515e93 100644 (file)
--- a/minsk.c
+++ b/minsk.c
@@ -9,11 +9,9 @@
  *     - time limit
  *     - error messages
  *     - debugging/play mode
- *     - implement shifts
- *     - which instructions should modify the accumulator?
  *     - implement printing
  *     - floating point?
- *     - simulate R1 and R2?
+ *     - we probably have to disable NOP
  */
 
 #include <stdio.h>
@@ -76,6 +74,12 @@ static int fracinrange(double d)
   return (d > -1. && d < 1.);
 }
 
+static int wexp(word w)
+{
+  int exp = w & 077;
+  return (w & 0100 ? -exp : exp);
+}
+
 static word mem[4096];
 
 static word rd(int addr)
@@ -158,7 +162,8 @@ static void parse_in(void)
     }
 }
 
-static word acc, prev_acc;
+static word acc;
+static word r1, r2, current_ins;
 static int flag_zero = 0;
 static int ip = 00050;                 // Standard program start location
 static int prev_ip;
@@ -166,7 +171,7 @@ static int prev_ip;
 static void stop(char *reason)
 {
   printf("MACHINE STOPPED -- %s\n", reason);
-  printf("IP:%04o ACC:%c%012llo\n", prev_ip, WF(acc));
+  printf("IP:%04o ACC:%c%012llo R1:%c%012llo R2:%c%012llo\n", prev_ip, WF(acc), WF(r1), WF(r2));
   exit(0);
 }
 
@@ -177,16 +182,19 @@ static void over(void)
 
 static void nofpu(void)
 {
+  acc = current_ins;
   stop("NO FPU");
 }
 
 static void notimp(void)
 {
+  acc = current_ins;
   stop("NOT IMPLEMENTED");
 }
 
 static void noins(void)
 {
+  acc = current_ins;
   stop("ILLEGAL INSTRUCTION");
 }
 
@@ -194,9 +202,10 @@ static void run(void)
 {
   for (;;)
     {
-      prev_acc = acc;
+      r2 = acc;
       prev_ip = ip;
       word w = mem[ip];
+      current_ins = w;
 
       int op = (w >> 30) & 0177;       // Operation code
       int ax = (w >> 28) & 3;          // Address extensions not supported
@@ -228,15 +237,16 @@ static void run(void)
       word a, b, c;
       long long aa, bb, cc;
       double ad, bd, cd;
+      int i;
 
       auto void afetch(void);
       void afetch(void)
        {
          if (op & 2)
-           a = prev_acc;
+           a = r2;
          else
            a = rd(yi);
-         b = rd(xi);
+         b = r1 = rd(xi);
        }
 
       auto void astore(word result);
@@ -277,8 +287,8 @@ static void run(void)
          nofpu();
        case 030 ... 033:       // FIX multiplication
          afetch();
+         // XXX: We ignore the rounding mode settings
          cd = wtofrac(a) * wtofrac(b);
-         // FIXME: Rounding?
          astore(wfromfrac(cd));
          break;
        case 034 ... 037:       // FP multiplication
@@ -296,7 +306,7 @@ static void run(void)
          break;
        case 044 ... 047:       // FP division
          nofpu();
-       case 050 ... 053:       // subtraction of abs values
+       case 050 ... 053:       // FIX subtraction of abs values
          afetch();
          cc = wabs(a) - wabs(b);
          if (!inrange(cc))
@@ -306,9 +316,27 @@ static void run(void)
        case 054 ... 057:       // FP subtraction of abs values
          nofpu();
        case 060 ... 063:       // Shift logical
-         notimp();     // XXX
+         afetch();
+         i = wexp(b);
+         if (i <= -37 || i >= 37)
+           astore(0);
+         else if (i >= 0)
+           astore((a << i) & WORD_MASK);
+         else
+           astore(a >> (-i));
+         break;
        case 064 ... 067:       // Shift arithmetical
-         notimp();     // XXX
+         afetch();
+         i = wexp(b);
+         aa = wabs(a);
+         if (i <= -36 || i >= 36)
+           cc = 0;
+         else if (i >= 0)
+           cc = (aa << i) & VAL_MASK;
+         else
+           cc = aa >> (-i);
+         astore((a & SIGN_MASK) | wfromll(cc));
+         break;
        case 070 ... 073:       // And
          afetch();
          astore(a&b);
@@ -319,7 +347,7 @@ static void run(void)
          break;
 
        case 0100:              // Halt
-         // r1 = rd(x);
+         r1 = rd(x);
          acc = rd(y);
          stop("HALTED");
        case 0103:              // I/O magtape
@@ -333,18 +361,18 @@ static void run(void)
        case 0107:              // Reverse tape
          notimp();
        case 0110:              // Move
-         wr(yi, rd(xi));
+         wr(yi, r1 = acc = rd(xi));
          break;
        case 0111:              // Move negative
-         wr(yi, rd(xi) ^ SIGN_MASK);
+         wr(yi, acc = (r1 = rd(xi)) ^ SIGN_MASK);
          break;
        case 0112:              // Move absolute value
-         wr(yi, rd(xi) & VAL_MASK);
+         wr(yi, acc = (r1 = rd(xi)) & VAL_MASK);
          break;
        case 0113:              // Read from keyboard
          notimp();
        case 0114:              // Copy sign
-         wr(yi, rd(yi) ^ (rd(xi) & SIGN_MASK));
+         wr(yi, acc = rd(yi) ^ ((r1 = rd(xi)) & SIGN_MASK));
          break;
        case 0115:              // Read code from R1 (obscure)
          notimp();
@@ -355,18 +383,19 @@ static void run(void)
        case 0120:              // Loop
          if (!ix)
            noins();
-         a = rd(ix);
+         a = r1 = rd(ix);
          aa = (a >> 24) & 017777;
          if (!aa)
            break;
          b = rd(y);            // (a mountain range near Prague)
-         wr(ix, ((aa-1) << 24) |
-                (((((a >> 12) & 07777) + (b >> 12) & 07777) & 07777) << 12) |
-                (((a & 07777) + (b & 07777)) & 07777));
+         acc = ((aa-1) << 24) |
+               (((((a >> 12) & 07777) + (b >> 12) & 07777) & 07777) << 12) |
+               (((a & 07777) + (b & 07777)) & 07777);
+         wr(ix, acc);
          ip = x & 07777;
          break;
        case 0130:              // Jump
-         wr(y, prev_acc);
+         wr(y, r2);
          ip = x & 07777;
          break;
        case 0131:              // Jump to subroutine
@@ -374,7 +403,7 @@ static void run(void)
          ip = x & 07777;
          break;
        case 0132:              // Jump if positive
-         if (wsign(prev_acc) >= 0)
+         if (wsign(r2) >= 0)
            ip = x & 07777;
          else
            ip = y & 07777;
@@ -405,6 +434,8 @@ static void run(void)
          notimp();
        case 0170:              // FIX multiplication, bottom part
          afetch();
+         if (wtofrac(a) * wtofrac(b) >= .1/(1ULL << 32))
+           over();
          acc = wfromll(((unsigned long long)wabs(a) * (unsigned long long)wabs(b)) & VAL_MASK);
          // XXX: What should be the sign? The book does not define that.
          break;
@@ -424,30 +455,33 @@ static void run(void)
        case 0173:              // Sub exponents
          nofpu();
        case 0174:              // Addition in one's complement
-         a = rd(xi);
+         a = r1 = rd(xi);
          b = rd(yi);
          c = a + b;
          if (c > VAL_MASK)
            c = c - VAL_MASK;
-         // XXX: What happens with the accumulator?
          wr(yi, c);
+         // XXX: The effect on the accumulator is undocumented, but likely to be as follows:
+         acc = c;
          break;
        case 0175:              // Normalization
          nofpu();
        case 0176:              // Population count
-         a = rd(xi);
+         a = r1 = rd(xi);
          cc = 0;
          for (int i=0; i<36; i++)
            if (a & (1ULL << i))
              cc++;
-         wr(yi, wfromll(cc));
+         // XXX: Guessing that acc gets a copy of the result
+         acc = wfromll(cc);
+         wr(yi, acc);
          break;
        default:
          noins();
        }
 
       flag_zero = !acc;
-      printf("\tACC:%c%012llo Z:%d\n", WF(acc), flag_zero);
+      printf("\tACC:%c%012llo R1:%c%012llo R2:%c%012llo Z:%d\n", WF(acc), WF(r1), WF(r2), flag_zero);
     }
 }