From 388ac6c4123c318d1005ca14625a4d374e3e7bf2 Mon Sep 17 00:00:00 2001
From: Arne Keller <arne.keller@posteo.de>
Date: Mon, 15 Mar 2021 15:00:24 +0100
Subject: [PATCH] Prime blocks finder + implicate printer

---
 src/lib.rs  | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/main.rs | 10 +++++++--
 2 files changed, 72 insertions(+), 2 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index f857a88..1950ed5 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -82,6 +82,70 @@ pub fn find_groups(func: &FunctionSpec, vars: &[Variable], typ: Output) -> Vec<V
 	groups
 }
 
+pub fn find_prime<'a>(func: &FunctionSpec, vars: &[Variable], typ: Output, blocks: &'a [Vec<(Variable, Output)>]) -> Vec<&'a [(Variable, Output)]> {
+	assert_eq!(func.len(), 2usize.pow(vars.len() as u32));
+
+	let block_masks = blocks.iter().map(|x| &**x)
+		.map(block_to_mask)
+		.collect::<Vec<_>>();
+
+	let mut prime = vec![false; blocks.len()];
+	'input: for input in 0..func.len() {
+		if func[input] != typ {
+			continue;
+		}
+		let mut matched = None;
+		for (i, (mask, inv_mask)) in block_masks.iter().enumerate() {
+			if input | mask == input && input & inv_mask == input {
+				if matched.is_none() {
+					matched = Some(i);
+				} else {
+					continue 'input;
+				}
+			}
+		}
+		if let Some(i) = matched {
+			prime[i] = true;
+		}
+	}
+	prime.into_iter().enumerate().filter(|&(_, prime)| prime).map(|(i, _)| &*blocks[i]).collect()
+}
+
+/// a ⊆ b
 fn subset_of<T: Eq>(a: &[T], b: &[T]) -> bool {
 	a.iter().all(|x| b.contains(x))
+}
+
+fn block_to_mask(block: &[(Variable, Output)]) -> (Variable, Variable) {
+	let mut mask = 0;
+	let mut inv_mask = !0;
+	for &(var, out) in block {
+		mask |= if out == One { var } else { 0 };
+		inv_mask ^= if out == Zero { var } else { 0 };
+	}
+	(mask, inv_mask)
+}
+
+pub fn print_implicate(vars: &[(Variable, Output)]) -> String {
+	let mut s = String::new();
+	for i in 0..vars.len() {
+		let (var, out) = vars[i];
+		if out == One {
+			s += "~";
+		}
+		s += print_var(var);
+		if i != vars.len() - 1 {
+			s += " v ";
+		}
+	}
+	s
+}
+
+fn print_var(var: Variable) -> &'static str {
+	match var {
+		A => "a",
+		B => "b",
+		C => "c",
+		_ => "?"
+	}
 }
\ No newline at end of file
diff --git a/src/main.rs b/src/main.rs
index 8110cdf..ebebea9 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -4,7 +4,13 @@ use kv::Output::*;
 fn main() {
 	let function = vec![0, 0, 1, 0, 0, 1, 1, 1].into_iter().map(Into::into).collect();
 	let groups = find_groups(&function, &mut [A, B, C], Zero);
-	for x in groups {
-		println!("{:?}", x);
+	println!("all:");
+	for x in &groups {
+		println!("{}", print_implicate(x));
+	}
+	println!("prime:");
+	let prime = find_prime(&function, &mut [A, B, C], Zero, &groups);
+	for x in prime {
+		println!("{}", print_implicate(&x));
 	}
 }