From 271500d4339ce3890c2c3e19ae7da9bc2e2c4049 Mon Sep 17 00:00:00 2001
From: d_m <d_m@plastic-idolatry.com>
Date: Thu, 9 Nov 2023 12:59:21 -0500
Subject: [PATCH] Implement bc15add with test.

---
 src/base3.c | 28 ++++++++++++++++++++++++++++
 src/bcb.c   | 28 ++++++++++++++++++++++++++++
 src/bcb.h   |  2 ++
 3 files changed, 58 insertions(+)

diff --git a/src/base3.c b/src/base3.c
index b694a24..eef6b0c 100644
--- a/src/base3.c
+++ b/src/base3.c
@@ -65,5 +65,33 @@ main(int argc, char **argv)
 		printf("%4d -> %4d ", 1 << i, uc15int(intuc15(1 << i))), phep(intuc15(1 << i), 5);
 		LB
 	}
+
+	printf("\nbc15 addition:\n");
+	int total = 0;
+	int passed = 0;
+	for(int i = -50; i <= 50; i += 1) {
+		for(int j = -50; j <= 50; j += 1) {
+			bc15 a = intbc15(i);
+			bc15 b = intbc15(j);
+			bc15 c = bc15add(a, b);
+			int k = bc15int(c);
+			int l = i + j;
+			total += 1;
+			if (k == l) {
+				passed += 1;
+			} else {
+				printf("FAIL  ");
+				printf("  % 3d + % 3d = % 5d (", i, j, k);
+				pbal(a, 7);
+				printf(" (+) ");
+				pbal(b, 7);
+				printf(" (=) ");
+				pbal(c, 7);
+				printf(")\n");
+			}
+		}
+	}
+	printf("  %d of %d test cases passed\n", passed, total);
+
 	return 0;
 }
diff --git a/src/bcb.c b/src/bcb.c
index a949ffc..6f68433 100644
--- a/src/bcb.c
+++ b/src/bcb.c
@@ -142,6 +142,34 @@ bc15int(bc15 t)
 	return acc;
 }
 
+bc15
+bc15add(bc15 a, bc15 b)
+{
+	bc15 acc = 0;
+	int i, carry = 0;
+	for (i = 0; i < 30 && (carry != 0 || (a>>i) != 0 || (b>>i) != 0); i += 2) {
+		int digit = carry;
+		carry = 0;
+		bc15carry((a >> i) & 0x3, &digit, &carry);
+		bc15carry((b >> i) & 0x3, &digit, &carry);
+		acc |= (digit << i);;
+	}
+	return acc;
+}
+
+void
+bc15carry(int next, int *digit, int *carry)
+{
+	int sum = *digit + next;
+	int part = sum & 0x3;
+	if (part == 2) {
+		*carry = (*carry + (sum >> 1)) & 0x3;
+		*digit = (sum ^ 4) >> 1;
+	} else {
+		*digit = part;
+	}
+}
+
 // Unsigned(TODO: migrate to 11-00-01 encoding)
 
 int
diff --git a/src/bcb.h b/src/bcb.h
index b7bc6d1..0360985 100644
--- a/src/bcb.h
+++ b/src/bcb.h
@@ -47,6 +47,8 @@ void pbc3(bc3 t);
 // 15 Trits
 bc15 intbc15(int n);
 int bc15int(bc15 t);
+bc15 bc15add(bc15 a, bc15 b);
+void bc15carry(int sum, int *digit, int *carry);
 
 // Unsigned
 int uc15int(uc15 t);
-- 
2.45.2