From c5d0ef8e53608da468f89837a12ab10ecc401978 Mon Sep 17 00:00:00 2001
From: Peter Mikkelsen <petermikkelsen10@gmail.com>
Date: Fri, 28 Jan 2022 21:49:14 +0000
Subject: =?UTF-8?q?Implement=20rotate=20first=20(=E2=8A=96)=20and=20rotate?=
 =?UTF-8?q?=20last=20(=E2=8C=BD)?=
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---
 apl9.h      |  2 ++
 functions.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 55 insertions(+), 2 deletions(-)

diff --git a/apl9.h b/apl9.h
index 2a7565f..ef1785b 100644
--- a/apl9.h
+++ b/apl9.h
@@ -349,6 +349,8 @@ Array *fnExcluding(Array *, Array *);
 Array *fnCatenateLast(Array *, Array *);
 Array *fnCatenateFirst(Array *, Array *);
 Array *fnReshape(Array *, Array *);
+Array *fnRotateLast(Array *, Array *);
+Array *fnRotateFirst(Array *, Array *);
 Array *fnSelfReference2(Array *, Array *);
 
 /* Monadic operators from operators.c */
diff --git a/functions.c b/functions.c
index d96deb6..997c1b4 100644
--- a/functions.c
+++ b/functions.c
@@ -110,8 +110,8 @@ fndyad dyadfunctiondefs[] = {
 	fnCatenateLast, /* , */
 	fnCatenateFirst, /* ⍪ */
 	fnReshape, /* ⍴ */
-	0, /* ⌽ */
-	0, /* ⊖ */
+	fnRotateLast, /* ⌽ */
+	fnRotateFirst, /* ⊖ */
 	0, /* ⍉ */
 	0, /* ⍎ */
 	0, /* ⍕ */
@@ -1327,6 +1327,57 @@ fnReshape(Array *left, Array *right)
 	return res;
 }
 
+Array *
+fnRotateLast(Array *left, Array *right)
+{
+	return rundfn(L"⍉(⍉⍺)⊖⍉⍵", nil, nil, left, right);
+}
+
+Array *
+fnRotateFirst(Array *left, Array *right)
+{
+	if(left->type != AtypeInt)
+		throwerror(nil, EType);
+
+	if(right->rank == 0 || right->size < 2)
+		return fnSame(right);
+
+	int i, j;
+	if(left->size == 1 && right->rank != 0){
+		vlong v = left->intdata[0];
+		left = allocarray(AtypeInt, right->rank-1, right->size / right->shape[0]);
+		for(i = 0; i < left->rank; i++)
+			left->shape[i] = right->shape[i+1];
+		for(i = 0; i < left->size; i++)
+			left->intdata[i] = v;
+	}else
+		left = fnSame(left);
+
+	if(left->rank != right->rank-1)
+		throwerror(nil, ERank);
+	for(i = 0; i < left->rank; i++)
+		if(left->shape[i] != right->shape[i+1])
+			throwerror(nil, EShape);
+
+	int n = right->shape[0];
+	for(i = 0; i < left->size; i++)
+		while(left->intdata[i] < 0)
+			left->intdata[i] += n;
+
+	Array *result = duparray(right);
+	for(i = 0; i < n; i++){
+		for(j = 0; j < left->size; j++){
+			vlong rot = left->intdata[j];
+			vlong from = j + ((i+rot)%n)*left->size;
+			vlong to = j + i*left->size;
+			memcpy(result->rawdata + to*datasizes[right->type],
+				right->rawdata + from*datasizes[right->type],
+				datasizes[right->type]);
+		}
+	}
+	return result;
+}
+
 Array *
 fnSelfReference2(Array *left, Array *right)
 {
-- 
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