implemented spec change: now cell 127 always return 1

README.md

@@ -14,8 +14,8 @@ programs and data. The only available data type is a floating point number,
 although some implementations may use fixed point numbers instead.
 
 Unlike 808UL, mu808 strictly defines support of up to 16384 data cells and
-up to 16383 program steps, with the program step 0 being unavailable and the
+up to 16383 program steps, with the program step 0 being unavailable, the
-data cell 0 always returning 0.
+data cell 0 always returning 0 and the data cell 127 always returning 1.
 
 On the machine start, both memory areas are initialized with zeroes and the
 interactive mode is entered which accepts instructions from the platform's
@@ -27,7 +27,8 @@ standard input.
 * ability to enter integer commands (positive and negative) into program memory;
 * ability to enter floating (or fixed) point numbers (positive and negative) at
   program runtime;
-* immutability of the data address 0 (must always return 0 when accessed).
+* immutability of the data address 0 (must always return 0 when accessed);
+* immutability of the data address 127 (must always return 1 when accessed).
 
 The following things are implementation-dependent:
 
@@ -191,6 +192,7 @@ The shortcut mnemonics for other operations are as follows:
 * `dca` is a shortcut to `cpy 0` (direct constant assignment)
 * `dva` is a shortcut to `cpy 1` (direct value assignment)
 * `iva` is a shortcut to `cpy 2` (indirect value assignment)
+* `inc` is a shortcut to `fma 127 127` (increment)
 * `mul` is a shortcut to `fma 0` (multiplication)
 * `exp` is a shortcut to `nel 0` (natural exponent)
 * `log` is a shortcut to `nel 1` (natural logarithm)
@@ -475,8 +477,8 @@ to store a constant 1 into some unused location, like 99. You can do this e.g.
 with the `set 1 0 99` operation. Then, let's go with three cases (assuming we
 have stored 1 into the data memory location 99):
 
-1. Incrementing a memory location is as easy as `fma 99 99 [loc]`.
+1. Incrementing a memory location is as easy as `fma 127 127 [loc]`.
-2. Adding two numbers at loc1 and loc2 into loc2: `fma [loc1] 99 [loc2]`.
+2. Adding two numbers at loc1 and loc2 into loc2: `fma [loc1] 127 [loc2]`.
 3. Multiplying two numbers at loc1 and loc2 into loc2: `fma 0 [loc1] [loc2]`.
 
 The only inconvenience with the FMA operation is that you need to sacrifice one

mu808.awk

@@ -27,6 +27,7 @@ function ilexec(lno, cmd, x, y, z,  halt, data_override, bcheck, i, v1, v2, v3)
   while(halt == 0) {
     if(traceflag) printf("PC: %hu INSTR: %hu %hu %hu %hu\n", lno, cmd, x, y, z)
     DMEM[0] = data_override = 0 # force the value at 0 to be always 0
+    DMEM[127] = 1 # force the value at 127 to always be 1
     bcheck = (x < MEMLIMIT) && (y < MEMLIMIT) && (z < MEMLIMIT)
     if(bcheck) {
       v1 = DMEM[x]; v2 = DMEM[y]; v3 = DMEM[z] # prefetch the memory values

mu808.b74

@@ -12,7 +12,7 @@
 210 IF IAT=1 THEN 220 ELSE 230
 220 X=INT(V1):Y=INT(V2):Z=INT(V3):IAT=0:GOTO 240
 230 X=A-CMD*10000:Y=INT(B/10000):Z=B-Y*10000
-240 V1,V2,V3,DMEM(0)=0
+240 V1,V2,V3,DMEM(0)=0:DMEM(127)=1
 250 IF CMD=5 THEN DMEM(Z)=X+(Y/10000):GOTO 180
 260 V1=DMEM(X):V2=DMEM(Y):V3=DMEM(Z)
 270 IF CMD=1 THEN 280 ELSE 420

mu808.c

@@ -76,6 +76,7 @@ void ilexec(ushort lno, ushort cmd, ushort x, ushort y, ushort z) {
   while(halt == 0) {
     if(traceflag) printf("PC: %hu INSTR: %hu %hu %hu %hu" NLC, lno, cmd, x, y, z);
     DMEM[0] = data_override = 0; /* force the value at 0 to be always 0 */
+    DMEM[127] = 1; /* force the value at 127 to always be 1 */
     bcheck = (x < MEMLIMIT) && (y < MEMLIMIT) && (z < MEMLIMIT);
     if(bcheck) {
       v1 = DMEM[x]; v2 = DMEM[y]; v3 = DMEM[z]; /* prefetch the memory values */

mu808.py

@@ -62,6 +62,7 @@ def ilexec(lno:int, cmd:int=0, x:int=0, y:int=0, z:int=0):
         if traceflag:
             print(f'PC: {lno} INSTR: {cmd} {x} {y} {z}')
         DMEM[0] = 0.0 # force the value at 0 to always be 0
+        DMEM[127] = 1.0 # force the value at 127 to always be 1
         data_override = False
         # perform a boundary check and prefetch the memory values
         bcheck = True

mu808asm.py

@@ -37,6 +37,7 @@ jmpfunc_shorts = {
     'dca': 'cpy 0',       # direct constant assignment
     'dva': 'cpy 1',       # direct value assignment
     'iva': 'cpy 2',       # indirect value assignment
+    'inc': 'fma 127 127', # increment
     'mul': 'fma 0',       # multiplication
     'exp': 'nel 0',       # natural exponent
     'log': 'nel 1',       # natural logarithm

mu8web/mu808-core.js

@@ -42,6 +42,7 @@ function createmu808(lineOut, charOut, lineIn) {
     var halt = 0, data_override = 0, bcheck, i, v1, v2, v3
     while(halt == 0) {
       v1 = v2 = v3 = data_override = DMEM[0] = 0 /* force the value at 0 to be always 0 */
+      DMEM[127] = 1 /* force the value at 127 to be always 1 */
       if(lno == 0) halt = 1 /* immediate instruction */
       if(runlimit > 0 && runcount > runlimit) {
         halt = 1