permacomputing

commit 8b6f7ad49221804ffaa621b150043d75d3fead9e
parent 0a44e126f2d8c7e09e94d78268b263a1da65cb0b
Author: neau <neau@web>
Date:   Wed, 22 Jun 2022 16:06:24 +0200

empty web commit

Diffstat:
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p-code.mdwn
 | 
21
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1 file changed, 20 insertions(+), 1 deletion(-)
diff --git a/p-code.mdwn b/p-code.mdwn
@@ -1,4 +1,4 @@
-In computer programming, a p-code machine is a [[virtual machine]] designed to execute the assembly language of a hypothetical CPU.
+A p-code machine is a [[virtual machine]] designed to execute the assembly language of a hypothetical CPU.
 
 [[Niklaus Wirth]] specified a simple p-code machine in the 1976 book Algorithms + Data Structures = Programs. The machine had 3 registers - a program counter p, a base register b, and a top-of-stack register t. There were 8 instructions:
 
@@ -11,6 +11,25 @@ In computer programming, a p-code machine is a [[virtual machine]] designed to e
     jmp 0, a  : jump to a
     jpc 0, a  : jump conditional to a[6]
 
+## Operations
+
+    0: begin {return}
+        t := b - 1; p := s[t + 3]; b := s[t + 2];
+    end;
+    1: s[t] := -s[t];
+    2: begin t := t - 1; s[t] := s[t] + s[t + 1] end;
+    3: begin t := t - 1; s[t] := s[t] - s[t + 1] end;
+    4: begin t := t - 1; s[t] := s[t] * s[t + 1] end;
+    5: begin t := t - 1; s[t] := s[t] div s[t + 1] end;
+    6: s[t] := ord(odd(s[t]));
+    8: begin t := t - 1; s[t] := ord(s[t] = s[t + 1]) end;
+    9: begin t := t - 1; s[t] := ord(s[t] <> s[t + 1]) end;
+    10: begin t := t - 1; s[t] := ord(s[t] < s[t + 1]) end;
+    11: begin t := t - 1; s[t] := ord(s[t] >= s[t + 1]) end;
+    12: begin t := t - 1; s[t] := ord(s[t] > s[t + 1]) end;
+    13: begin t := t - 1; s[t] := ord(s[t] <= s[t + 1]) end;
+
+
 See more:
 
 * [On Wikipedia](https://en.wikipedia.org/wiki/P-code_machine)