Tidied up to be used as little example

.gitignore

@@ -0,0 +1 @@
+*~

README.md

@@ -1,2 +1,42 @@
-# subleq
-SUBLEQ SIC/OISC
+# SUBLEQ SIC/OISC
+
+This is a simple interpreter for a single-insutruction computer.
+
+The single instruction is SUBLEQ (subtract and branch if less-than-or-equal-to 0)
+
+Example: subleq a b c
+ - Subtract value in memory address a from value in memory address b
+ - store result in memory address b
+ - if the value is less than or equal to 0, jump to c
+- Programs are made of groups of 3 values (a, b, c)
+- Code and data share the same memory
+- A jump to -1 terminates
+- A jump to -2 just moves forward to the next group of 3 (essentially means "no jump", just continue)
+- Writing to address -1 outputs an ascii value
+
+## Example:
+
+If we have a piece of subleq code: `9 10 3 11 9 0 12 12 0 14 100 -1 0`
+
+It would be executed like this:
+
+```
+9 10 3, 11 9 0, 12 12 0, 14 100 -1, 0
+execute at 0
+9 10 3, 11 9 0, 12 12 0, 14 86 -1, 0
+execute at 3 (not jumping, just moving on)
+9 10 3, 11 9 0, 12 12 0, 15 86 -1, 0
+execute at 6 (not jumping, just moving on)
+9 10 3, 11 9 0, 12 12 0, 15 86 -1, 0
+execute at 0 (jumped!)
+9 10 3, 11 9 0, 12 12 0, 15 71 -1, 0
+execute at 3 (not jumping, just moving on)
+9 10 3, 11 9 0, 12 12 0, 16 71 -1, 0
+execute at 6 (not jumping, just moving on)
+9 10 3, 11 9 0, 12 12 0, 16 71 -1, 0
+execute at 0 (jumped!)
+9 10 3, 11 9 0, 12 12 0, 16 55 -1, 0
+...and so on
+```
+
+Note that any instruction that doesn't jump is automatically followed by a jump forward by 3 to get to the next set of three values.

generator/generate.py

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+data="This is a test of the emergency broadcast system\n"
+l=len(data)
+ascii_vals=[str(ord(i)) for i in data]
+ascii_string=""
+c=0
+for i in ascii_vals:
+    c=(c+1)%3
+    ascii_string+=i+", "
+    if c==0:
+        ascii_string+="\n"
+
+
+ascii_string+="0"
+
+code="""21,  -1,  -2,  
+19,  20,  -1, 
+18,   0,  -2,     
+17,  17,   0, 
+0,   0,   0, 
+0,   0,   0, 
+-1,   1,  %i, 
+%s
+"""%(l,ascii_string)
+
+print(code)

subleq.py

@@ -1,23 +1,35 @@
-prog = [ 21,  -1,  -2,  #0 
-         19,  20,  -1,  #3 
-         18,   0,  -2,  #6     
-         17,  17,   0,  #9 
+#Example program
+prog = [ 21,  -1,  -2,  #0  #Print loc 21
+         19,  20,  -1,  #3  #Subtract 1 from pos 20, quit when 0
+         18,   0,  -2,  #6  #Add one to pos 0     
+         17,  17,   0,  #9  #Jump to pos 0
           0,   0,   0,  #12
           0,   0,   0,  #15
-         -1,   1,  13,  #18
-         72, 101, 108,  #21
-        108, 111,  32,  #24
-         87, 111, 114,  #27
-        108, 100,  33,  #30
-         10]            #33
+         -1,   1,  13,  #18 Pos 20 is string length
+         72, 101, 108,  #21 #Data begins here 
+        108, 111,  32,
+         87, 111, 114,
+        108, 100,  33,
+         10]
 
-pc=0  #Program counter.  The pointer to where we are
-
-out="" #Somewhere to collect the output to display at the end
+pc=0
+c=0
+out=""
 while True:
-    #Load the next 3 values into a, b, c
+    c+=1
     a,b,c=prog[pc:pc+3]
-
-    #now what?
-
-print out
+    if c==-2:
+        c=pc+3
+    pc+=3
+    if b>=0:
+        prog[b]-=prog[a]
+        result=prog[b]
+    else:
+        result=-1
+        if b==-1:
+            out+= chr(prog[a])
+    if result<=0:
+        pc=c
+    if pc<0:
+        break
+print(out)