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Tidied up to be used as little example
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James Shuttleworth
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Sep 15, 2021
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*~ |
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# subleq | ||
SUBLEQ SIC/OISC | ||
# SUBLEQ SIC/OISC | ||
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This is a simple interpreter for a single-insutruction computer. | ||
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The single instruction is SUBLEQ (subtract and branch if less-than-or-equal-to 0) | ||
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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 | ||
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## Example: | ||
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If we have a piece of subleq code: `9 10 3 11 9 0 12 12 0 14 100 -1 0` | ||
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It would be executed like this: | ||
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``` | ||
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 | ||
``` | ||
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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. |
611
details.org
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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" | ||
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ascii_string+="0" | ||
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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) | ||
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print(code) |
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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] | ||
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pc=0 #Program counter. The pointer to where we are | ||
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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] | ||
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#now what? | ||
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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) |