From 58a17583638f950fb04032984334cc68ed488f16 Mon Sep 17 00:00:00 2001
From: Bill Currie <bill@taniwha.org>
Date: Mon, 28 Aug 2023 20:32:29 +0900
Subject: [PATCH] [qfcc] Implement the regressive product

That went surprisingly well (but it is built up from other ops, so
pretty easy, really).
---
 tools/qfcc/source/expr_algebra.c | 6 ++++--
 tools/qfcc/source/qc-parse.y     | 1 +
 tools/qfcc/test/pga2d.r          | 5 +++++
 3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/tools/qfcc/source/expr_algebra.c b/tools/qfcc/source/expr_algebra.c
index ff86773de..31a2849d5 100644
--- a/tools/qfcc/source/expr_algebra.c
+++ b/tools/qfcc/source/expr_algebra.c
@@ -1342,8 +1342,10 @@ geometric_product (expr_t *e1, expr_t *e2)
 static expr_t *
 regressive_product (expr_t *e1, expr_t *e2)
 {
-	notice (e1, "not implemented");
-	return 0;
+	auto a = algebra_dual (e1);
+	auto b = algebra_dual (e2);
+	auto c = outer_product (a, b);
+	return algebra_dual (c);
 }
 
 static expr_t *
diff --git a/tools/qfcc/source/qc-parse.y b/tools/qfcc/source/qc-parse.y
index a0973228d..14fba3772 100644
--- a/tools/qfcc/source/qc-parse.y
+++ b/tools/qfcc/source/qc-parse.y
@@ -1773,6 +1773,7 @@ expr
 	| expr CROSS expr			{ $$ = binary_expr (CROSS, $1, $3); }
 	| expr DOT expr				{ $$ = binary_expr (DOT, $1, $3); }
 	| expr WEDGE expr			{ $$ = binary_expr (WEDGE, $1, $3); }
+	| expr REGRESSIVE expr		{ $$ = binary_expr (REGRESSIVE, $1, $3); }
 	;
 
 texpr
diff --git a/tools/qfcc/test/pga2d.r b/tools/qfcc/test/pga2d.r
index eade23e33..6074fd46d 100644
--- a/tools/qfcc/test/pga2d.r
+++ b/tools/qfcc/test/pga2d.r
@@ -265,5 +265,10 @@ main (void)
 				s.scalar, s.bvec);
 		return 1;
 	}
+	auto line = bvec ∨ bvecb;
+	if ((dvec3)line != '-11 8 34'd) {
+		printf ("bvec ∨ bvecb != '-11 8 34': %lv\n", line);
+		return 1;
+	}
 	return 0;		// to survive and prevail :)
 }