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+;;; Chickadee Game Toolkit
+;;; Copyright © 2017 David Thompson <davet@gnu.org>
+;;;
+;;; Chickadee is free software: you can redistribute it and/or modify
+;;; it under the terms of the GNU General Public License as published
+;;; by the Free Software Foundation, either version 3 of the License,
+;;; or (at your option) any later version.
+;;;
+;;; Chickadee is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;;; General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with this program.  If not, see
+;;; <http://www.gnu.org/licenses/>.
+
+(define-module (chickadee math easings)
+  #:use-module (chickadee math)
+  #:export (linear
+            smoothstep
+            ease-in-quad
+            ease-out-quad
+            ease-in-out-quad
+            ease-in-cubic
+            ease-out-cubic
+            ease-in-out-cubic
+            ease-in-quart
+            ease-out-quart
+            ease-in-out-quart
+            ease-in-quint
+            ease-out-quint
+            ease-in-out-quint
+            ease-in-sine
+            ease-out-sine
+            ease-in-out-sine))
+
+(define-inlinable (linear t)
+  t)
+
+(define-inlinable (smoothstep t)
+  (* t t (- 3 (* 2 t))))
+
+(define-inlinable (ease-in-quad t)
+  (* t t))
+
+(define-inlinable (ease-out-quad t)
+  (* t (- 2.0 t)))
+
+(define-inlinable (ease-in-out-quad t)
+  (if (< t 0.5)
+      (* 2.0 t t)
+      (- (* (- 4 (* 2.0 t)) t) 1.0)))
+
+(define-inlinable (ease-in-cubic t)
+  (* t t t))
+
+(define-inlinable (ease-out-cubic t)
+  (let ((t* (- t 1.0)))
+    (+ 1.0 (* t* t* t*))))
+
+(define-inlinable (ease-in-out t)
+  (if (< t 0.5)
+      (* 4.0 t t t)
+      (+ 1.0
+         (* (- t 1.0)
+            (* 2 (- t 2.0))
+            (* 2 (- t 2.0))))))
+
+(define-inlinable (ease-in-quart t)
+  (* t t t t))
+
+(define-inlinable (ease-out-quart t)
+  (let ((t* (- t 1.0)))
+    (- 1.0 (* t* t* t* t*))))
+
+(define-inlinable (ease-in-out-quart t)
+  (if (< t 0.5)
+      (* 8.0 t t t t)
+      (let ((t* (- t 1.0)))
+        (- 1.0 (* 8.0 t* t* t* t*)))))
+
+(define-inlinable (ease-in-quint t)
+  (* t t t t t))
+
+(define-inlinable (ease-out-quint t)
+  (let ((t* (- t 1.0)))
+    (+ 1.0 (* t* t* t* t* t*))))
+
+(define-inlinable (ease-in-out-quint t)
+  (if (< t 0.5)
+      (* 16.0 t t t t t)
+      (let ((t* (- t 1.0)))
+        (+ 1.0 (* 16.0 t* t* t* t* t*)))))
+
+(define-inlinable (ease-in-sine t)
+  (+ (* (- t) (cos (* t pi/2))) t))
+
+(define-inlinable (ease-out-sine t)
+  (* t (sin (* t pi/2))))
+
+(define-inlinable (ease-in-out-sine t)
+  (* (/ t -2)
+     (1- (cos (* t pi)))))